Genetic and Metabolic Disorders — MCQs

Q: A 4-year-old boy presents to his pediatrician for severe developmental delay. On exam he is noted to have macroorchidism, hypertelorism, large protruding ears, a large jaw, and a long thin face. Suspicious of what the diagnosis may be, the pediatrician orders a PCR and DNA sequencing. The results reveal an expansion of 250 repeats of CGG. What is the diagnosis of the boy?

Fragile X syndrome. ***Fragile X syndrome*** - The combination of **developmental delay**, characteristic physical features (**macroorchidism, large protruding ears, long thin face, large jaw**), and a **CGG repeat expansion** (250 repeats) is pathognomonic for Fragile X syndrome. - This is an **X-linked disorder** caused by an expansion of CGG trinucleotide repeats in the *FMR1* gene, leading to reduced or absent fragile X mental retardation protein (FMRP). *Huntington's disease* - Characterized by **chorea**, psychiatric symptoms, and cognitive decline, typically manifesting in adulthood, not early childhood developmental delay. - Caused by a **CAG trinucleotide repeat expansion** in the *HTT* gene, not CGG. *Spinal and bulbar muscular atrophy* - This is an **X-linked recessive** neurodegenerative disorder leading to muscle weakness and atrophy, which usually presents in adulthood. - It is caused by a **CAG repeat expansion** in the androgen receptor gene. *Myotonic dystrophy type 1* - Presents with progressive **muscle wasting and weakness**, myotonia, cataracts, and cardiac conduction defects, typically later in childhood or adulthood. - Caused by a **CTG trinucleotide repeat expansion** in the *DMPK* gene. *Friedreich ataxia* - Characterized by progressive **ataxia**, dysarthria, and loss of vibration/proprioception, usually beginning in childhood or adolescence. - Caused by a **GAA trinucleotide repeat expansion** in the *FXN* gene.

Q: An 8-month-old boy is brought to the physician for the evaluation of shortening of his arms and legs. The parents report that they have also noticed that their son's head is progressively enlarging. The patient was born at term via vaginal delivery. There is no personal or family history of serious illness. His immunizations are up-to-date. He is at the 3rd percentile for height, 25th percentile for weight, and 95th percentile for head circumference. Examination shows macrocephaly and prominent brow bones. The extremities are short and plump. Muscle strength is 3/5 in all muscle groups. Deep tendon reflexes are 4+ bilaterally. An x-ray of the lateral skull shows midfacial hypoplasia and frontal prominence. X-rays of the spine show abnormally narrow interpedicular distance. Which of the following is the most appropriate next step in management?

CT scan of the head. The patient's features, including **shortening of arms and legs**, **progressively enlarging head with macrocephaly**, **prominent brow bones**, **midfacial hypoplasia**, and **frontal prominence**, are classical signs of **achondroplasia**. In patients with achondroplasia, **hydrocephalus** due to impaired cerebrospinal fluid outflow at the foramen magnum is a common and serious complication, making a CT scan of the head the most appropriate next step to assess for this [1]. The patient presents with significant and progressive clinical signs such as **abnormal growth parameters**, **macrocephaly**, and **neurological symptoms** (hyperreflexia, muscle weakness), which warrant further investigation to identify anomalies of skull configuration [1].

Q: Ectopia lentis in a child is seen in which of the following diseases?

Homocystinuria. ***Homocystinuria*** - Ectopia lentis (lens dislocation) is a characteristic feature of **homocystinuria**, often presenting at a young age. - The dislocation in homocystinuria is typically **inferomedial (inferonasally)** due to weakened zonular fibers. - Homocystinuria is an **inborn error of methionine metabolism** with elevated homocysteine levels. *Marfan syndrome* - While **Marfan syndrome** is the most common cause of ectopia lentis, the lens typically dislocates **superiorly and temporally**. - Marfan syndrome is a connective tissue disorder but is not primarily a metabolic disorder like homocystinuria. - Both conditions can present with ectopia lentis, but the direction of dislocation and associated features differ. *Sarcoidosis* - Ocular manifestations of sarcoidosis usually include **uveitis**, **conjunctivitis**, and **retinal vasculitis**, but not typically ectopia lentis. - Sarcoidosis is a multisystem granulomatous disease and is rare in young children presenting with ectopia lentis. *Wilson disease* - **Kayser-Fleischer rings**, which are deposits of copper in the cornea, are pathognomonic for Wilson disease. - Ocular involvement in Wilson disease does not typically involve ectopia lentis. *Alkaptonuria* - This condition is characterized by the accumulation of **homogentisic acid**, leading to **ochronosis** (black pigmentation) in cartilaginous tissues and urine that turns black on standing. - Ocular manifestations can include scleral pigmentation, but ectopia lentis is not a feature of alkaptonuria.

Q: Which of the following is the least common cause of ambiguous genitalia in a female child

Fetal placental aromatase deficiency. ***Fetal placental aromatase deficiency*** - This condition is exceedingly rare and is considered one of the **least common genetic causes** of ambiguous genitalia in a female. - Deficiency of **aromatase** in the placenta prevents the conversion of androgens to estrogens, leading to **masculinization of a female fetus**, but this pathway is only a minor contributor to fetal androgenization. *WNT-4 gene mutation* - **WNT-4** is crucial for **female sexual differentiation** and acts as an anti-testis factor. - Mutations can lead to **Müllerian aplasia** and variable degrees of virilization in genetic females, making it a recognized, though not the most common, cause of ambiguous genitalia. *Congenital adrenal hyperplasia* - This is the **most common cause** of ambiguous genitalia in a female, primarily due to **21-hydroxylase deficiency**. - Excess adrenal androgens lead to **virilization** of the external genitalia in genetic females. *Maternal androgen exposure* - Virilization can occur from **maternal sources** such as androgen-secreting tumors, exogenous androgen use, or aromatase inhibitors during pregnancy. - This is an **uncommon but recognized cause**, more frequent than aromatase deficiency but far less common than CAH. *Fetal placental steroid sulfatase deficiency* - This deficiency typically results in **low maternal estrogen levels** and can cause **placental insufficiency** and abnormalities in labor, but it does **not directly cause ambiguous genitalia** in a female fetus. - While it affects steroid metabolism, it does not lead to the accumulation of androgens necessary for virilization of female external genitalia.

Q: All are features of Osteogenesis imperfecta except-

Cataract. ***Cataract*** - **Cataracts** are not typically associated with **osteogenesis imperfecta (OI)**. Ocular manifestations in OI predominantly involve the sclera. - While other connective tissue disorders might feature cataracts, they are not a characteristic diagnostic or common finding in OI. *Multiple fractures* - **Multiple fractures** with minimal or no trauma are a hallmark of **osteogenesis imperfecta**, due to defective **type I collagen** synthesis. - The severity and frequency of these fractures vary depending on the specific type of OI. *Blue sclera* - **Blue sclera** is a classic feature of **osteogenesis imperfecta**, caused by the underlying choroidal veins showing through a thinned, translucent sclera due to defective **collagen**. - This is a key diagnostic clue, often present from birth or early childhood. *Hearing loss* - **Hearing loss** is common in **osteogenesis imperfecta**, particularly the **conductive type**, but can also be sensorineural or mixed. - It results from **ossicular chain abnormalities**, otosclerosis, or fragility of the middle ear bones, all related to the collagen defect. *Dentinogenesis imperfecta* - **Dentinogenesis imperfecta** is a characteristic dental manifestation of **osteogenesis imperfecta**, seen in approximately 50% of cases. - It involves defective dentin formation leading to discolored (gray, blue, or brown), translucent teeth that are prone to wear and fracture due to the same collagen defect affecting bones.

Q: A 10-year-old male child presented with complaints of severe progressive weakness of bilateral lower limbs, imbalance in walking, and slurred speech for the past 3 years, with recent development of visual disturbance, behavioral symptoms, and rapid progression of motor weakness. MRI was performed at the time of presentation. What is the diagnosis?

X-linked adrenoleukodystrophy. ***X-linked adrenoleukodystrophy*** - This condition presents in males, typically between ages 4 and 10 years, with progressive neurological deterioration including **motor weakness**, **ataxia**, **visual disturbances**, and **behavioral changes**, consistent with the patient's symptoms. - The disease involves demyelination in the central nervous system due to the accumulation of **very long-chain fatty acids (VLCFAs)** and is inherited in an **X-linked recessive pattern**. *Alexander's disease* - This typically presents in infancy or early childhood with **megalencephaly**, developmental delay, and seizures, which are not described in this patient. - MRI often shows characteristic frontal white matter changes and **periventricular rim enhancement**. *Krabbe's disease* - This is an autosomal recessive disorder that usually presents in infants, with irritability, feeding difficulties, and rapid neurodegeneration, leading to **severe developmental regression**. - It involves the accumulation of **galactocerebroside** in neural tissues due to **beta-galactocerebrosidase deficiency**. *Metachromatic leukodystrophy* - This is an autosomal recessive lysosomal storage disorder that can present in late infancy, juvenile, or adult forms with progressive **demyelination** and neurological deficits. - While it causes **motor weakness** and cognitive decline, it often involves **peripheral neuropathy** and is characterized by the accumulation of **sulfatides**, not VLCFAs. *Canavan disease* - This is an autosomal recessive disorder caused by **aspartoacylase deficiency** leading to accumulation of **N-acetylaspartic acid (NAA)**. - Typically presents in early infancy (3-6 months) with **hypotonia**, **macrocephaly**, and **severe developmental delay**, earlier than the presentation in this case. - MRI shows diffuse white matter changes with characteristic involvement of subcortical U-fibers.

Q: X-linked disease leading to intellectual disability is -

Fragile-X syndrome. ***Fragile-X syndrome*** - This is the most common inherited cause of **intellectual disability** and is inherited in an **X-linked dominant pattern**. - It is caused by an expansion of a **CGG trinucleotide repeat** in the *FMR1* gene on the X chromosome. *Down syndrome* - This is a **chromosomal disorder** (trisomy 21), not X-linked. - It is the most common **genetic cause** of intellectual disability overall, resulting from an extra copy of chromosome 21. *Tuberous sclerosis* - This is an **autosomal dominant** disorder, not X-linked. - It involves the growth of **benign tumors** in various organs, including the brain, skin, kidneys, and heart. *Phenylketonuria* - This is an **autosomal recessive** metabolic disorder, not X-linked. - It results from a deficiency of the enzyme **phenylalanine hydroxylase**, leading to a buildup of phenylalanine. *Myotonic dystrophy* - This is an **autosomal dominant** disorder, not X-linked. - It is characterized by progressive **muscle wasting** and **myotonia** (delayed muscle relaxation).

Q: A male child with Fanconi syndrome with nephrocalcinosis has a variant of dent disease. All are true except :

Similar presentation in father. ***Similar presentation in father*** - Dent disease is an **X-linked recessive disorder** primarily affecting males due to mutations in the *CLCN5* or *OCRL1* genes. - While the father carries the Y chromosome and does not have the gene mutation, the mother is an asymptomatic carrier, passing the disease-causing allele to her sons. - **The father cannot present with the same X-linked condition** as he passes only his Y chromosome to male offspring. *Proteinuria* - **Low molecular weight proteinuria** is a hallmark of Dent disease and Fanconi syndrome, resulting from impaired reabsorption in the proximal tubules. - This is a direct consequence of the tubular dysfunction characteristic of these conditions. *Rickets* - **Rickets** can develop due to the renal phosphate wasting (hypophosphatemia) and vitamin D abnormalities (impaired activation) seen in Dent disease and Fanconi syndrome. - These bone manifestations are common complications of chronic kidney tubule dysfunction in children. *Hypercalciuria* - **Hypercalciuria** is a primary feature of Dent disease, leading to nephrocalcinosis and nephrolithiasis. - This excessive urinary calcium excretion contributes to the formation of kidney stones and calcification of renal tissue. *Progressive chronic kidney disease* - **Progressive CKD** is a recognized long-term complication of Dent disease, with many patients developing end-stage renal disease (ESRD) by adulthood. - The chronic tubular dysfunction and recurrent nephrolithiasis contribute to progressive nephron loss over time.

Q: A 10-year-old child presents with fever since 24 hours. History reveals 3 episodes of chest infection and passage of bulky, foul smelling stools. The most probable diagnosis is?

Cystic fibrosis. ***Cystic fibrosis*** - This genetic disorder causes defective **chloride transport**, leading to thick secretions in various organs, including the lungs and pancreas. - Recurrent **chest infections** are due to thick mucus trapping bacteria in the airways, and **bulky, foul-smelling stools** result from pancreatic insufficiency and malabsorption. *Crigler-Najjar syndrome* - This is a rare **genetic disorder** affecting bilirubin metabolism, leading to severe unconjugated hyperbilirubinemia. - Its primary presentation is **jaundice** and potential neurologic complications (**kernicterus**), not recurrent respiratory infections or steatorrhea. *Maple syrup urine disease* - This is an **autosomal recessive metabolic disorder** affecting the metabolism of branched-chain amino acids (leucine, isoleucine, valine). - It presents with characteristic **sweet-smelling urine** and severe neurological dysfunction, not primarily respiratory or gastrointestinal symptoms. *Bilirubin conjugation defect* - This is a broad term that can encompass several conditions like Crigler-Najjar syndrome or Gilbert's syndrome, all primarily presenting with **jaundice** due to impaired bilirubin processing. - It does not explain the recurrent chest infections or malabsorptive stools described in the child. *Shwachman-Diamond syndrome* - This is a rare **autosomal recessive disorder** featuring bone marrow dysfunction, pancreatic insufficiency, and skeletal abnormalities. - While it can cause malabsorption and increased infection risk due to **neutropenia**, the pattern of recurrent chest infections with steatorrhea is more classic for cystic fibrosis, which has a higher prevalence.

Q: All of the following are seen in Fragile X syndrome except:

Female preponderance. ***Female preponderance*** - **Fragile X syndrome** primarily affects males more severely due to it being an **X-linked dominant inheritance pattern** with variable expression and penetrance. - While females can be carriers or mildly affected, the full syndrome with significant intellectual disability and physical features is much more common in males. *Autism* - **Autistic-like behaviors** and **autism spectrum disorder** are frequently observed in individuals with Fragile X syndrome. - This is a common **neurodevelopmental comorbidity** associated with the genetic mutation. *Cardiac murmurs* - **Mitral valve prolapse (MVP)** is a common cardiac anomaly found in individuals with Fragile X syndrome, which can present as a **cardiac murmur**. - This is one of the associated physical features of the syndrome, likely due to connective tissue abnormalities. *Mental retardation* - **Intellectual disability**, ranging from mild to severe, is a **hallmark feature** of Fragile X syndrome. - It is the **most common inherited cause of intellectual disability**. *Macro-orchidism* - **Post-pubertal macroorchidism** (enlarged testicles) is seen in approximately **80% of adult males** with Fragile X syndrome. - This is one of the characteristic **physical features** associated with the condition.

A 4-year-old boy presents to his pediatrician for severe developmental delay. On exam he is noted to have macroorchidism, hypertelorism, large protruding ears, a large jaw, and a long thin face. Suspicious of what the diagnosis may be, the pediatrician orders a PCR and DNA sequencing. The results reveal an expansion of 250 repeats of CGG. What is the diagnosis of the boy?

An 8-month-old boy is brought to the physician for the evaluation of shortening of his arms and legs. The parents report that they have also noticed that their son's head is progressively enlarging. The patient was born at term via vaginal delivery. There is no personal or family history of serious illness. His immunizations are up-to-date. He is at the 3rd percentile for height, 25th percentile for weight, and 95th percentile for head circumference. Examination shows macrocephaly and prominent brow bones. The extremities are short and plump. Muscle strength is 3/5 in all muscle groups. Deep tendon reflexes are 4+ bilaterally. An x-ray of the lateral skull shows midfacial hypoplasia and frontal prominence. X-rays of the spine show abnormally narrow interpedicular distance. Which of the following is the most appropriate next step in management?

Ectopia lentis in a child is seen in which of the following diseases?

Which of the following is the least common cause of ambiguous genitalia in a female child

All are features of Osteogenesis imperfecta except-

A 10-year-old male child presented with complaints of severe progressive weakness of bilateral lower limbs, imbalance in walking, and slurred speech for the past 3 years, with recent development of visual disturbance, behavioral symptoms, and rapid progression of motor weakness. MRI was performed at the time of presentation. What is the diagnosis?

X-linked disease leading to intellectual disability is -

A male child with Fanconi syndrome with nephrocalcinosis has a variant of dent disease. All are true except :

A 10-year-old child presents with fever since 24 hours. History reveals 3 episodes of chest infection and passage of bulky, foul smelling stools. The most probable diagnosis is?

Q10

All of the following are seen in Fragile X syndrome except:

Genetic and Metabolic Disorders US Medical PG Practice Questions and MCQs

Question 1: A 4-year-old boy presents to his pediatrician for severe developmental delay. On exam he is noted to have macroorchidism, hypertelorism, large protruding ears, a large jaw, and a long thin face. Suspicious of what the diagnosis may be, the pediatrician orders a PCR and DNA sequencing. The results reveal an expansion of 250 repeats of CGG. What is the diagnosis of the boy?

A. Huntington's disease
B. Spinal and bulbar muscular atrophy
C. Myotonic dystrophy type 1
D. Fragile X syndrome (Correct Answer)
E. Friedreich ataxia

Explanation: ***Fragile X syndrome*** - The combination of **developmental delay**, characteristic physical features (**macroorchidism, large protruding ears, long thin face, large jaw**), and a **CGG repeat expansion** (250 repeats) is pathognomonic for Fragile X syndrome. - This is an **X-linked disorder** caused by an expansion of CGG trinucleotide repeats in the *FMR1* gene, leading to reduced or absent fragile X mental retardation protein (FMRP). *Huntington's disease* - Characterized by **chorea**, psychiatric symptoms, and cognitive decline, typically manifesting in adulthood, not early childhood developmental delay. - Caused by a **CAG trinucleotide repeat expansion** in the *HTT* gene, not CGG. *Spinal and bulbar muscular atrophy* - This is an **X-linked recessive** neurodegenerative disorder leading to muscle weakness and atrophy, which usually presents in adulthood. - It is caused by a **CAG repeat expansion** in the androgen receptor gene. *Myotonic dystrophy type 1* - Presents with progressive **muscle wasting and weakness**, myotonia, cataracts, and cardiac conduction defects, typically later in childhood or adulthood. - Caused by a **CTG trinucleotide repeat expansion** in the *DMPK* gene. *Friedreich ataxia* - Characterized by progressive **ataxia**, dysarthria, and loss of vibration/proprioception, usually beginning in childhood or adolescence. - Caused by a **GAA trinucleotide repeat expansion** in the *FXN* gene.

Question 2: An 8-month-old boy is brought to the physician for the evaluation of shortening of his arms and legs. The parents report that they have also noticed that their son's head is progressively enlarging. The patient was born at term via vaginal delivery. There is no personal or family history of serious illness. His immunizations are up-to-date. He is at the 3rd percentile for height, 25th percentile for weight, and 95th percentile for head circumference. Examination shows macrocephaly and prominent brow bones. The extremities are short and plump. Muscle strength is 3/5 in all muscle groups. Deep tendon reflexes are 4+ bilaterally. An x-ray of the lateral skull shows midfacial hypoplasia and frontal prominence. X-rays of the spine show abnormally narrow interpedicular distance. Which of the following is the most appropriate next step in management?

A. Reassurance
B. CT scan of the head (Correct Answer)
C. Growth hormone therapy
D. MRI of cervical spine
E. Bisphosphonate therapy

Explanation: The patient's features, including **shortening of arms and legs**, **progressively enlarging head with macrocephaly**, **prominent brow bones**, **midfacial hypoplasia**, and **frontal prominence**, are classical signs of **achondroplasia**. In patients with achondroplasia, **hydrocephalus** due to impaired cerebrospinal fluid outflow at the foramen magnum is a common and serious complication, making a CT scan of the head the most appropriate next step to assess for this [1]. The patient presents with significant and progressive clinical signs such as **abnormal growth parameters**, **macrocephaly**, and **neurological symptoms** (hyperreflexia, muscle weakness), which warrant further investigation to identify anomalies of skull configuration [1].

Question 3: Ectopia lentis in a child is seen in which of the following diseases?

A. Sarcoidosis
B. Wilson disease
C. Homocystinuria (Correct Answer)
D. Alkaptonuria
E. Marfan syndrome

Explanation: ***Homocystinuria*** - Ectopia lentis (lens dislocation) is a characteristic feature of **homocystinuria**, often presenting at a young age. - The dislocation in homocystinuria is typically **inferomedial (inferonasally)** due to weakened zonular fibers. - Homocystinuria is an **inborn error of methionine metabolism** with elevated homocysteine levels. *Marfan syndrome* - While **Marfan syndrome** is the most common cause of ectopia lentis, the lens typically dislocates **superiorly and temporally**. - Marfan syndrome is a connective tissue disorder but is not primarily a metabolic disorder like homocystinuria. - Both conditions can present with ectopia lentis, but the direction of dislocation and associated features differ. *Sarcoidosis* - Ocular manifestations of sarcoidosis usually include **uveitis**, **conjunctivitis**, and **retinal vasculitis**, but not typically ectopia lentis. - Sarcoidosis is a multisystem granulomatous disease and is rare in young children presenting with ectopia lentis. *Wilson disease* - **Kayser-Fleischer rings**, which are deposits of copper in the cornea, are pathognomonic for Wilson disease. - Ocular involvement in Wilson disease does not typically involve ectopia lentis. *Alkaptonuria* - This condition is characterized by the accumulation of **homogentisic acid**, leading to **ochronosis** (black pigmentation) in cartilaginous tissues and urine that turns black on standing. - Ocular manifestations can include scleral pigmentation, but ectopia lentis is not a feature of alkaptonuria.

Question 4: Which of the following is the least common cause of ambiguous genitalia in a female child

A. WNT-4 gene mutation
B. Congenital adrenal hyperplasia
C. Fetal placental aromatase deficiency (Correct Answer)
D. Fetal placental steroid sulfatase deficiency
E. Maternal androgen exposure

Explanation: ***Fetal placental aromatase deficiency*** - This condition is exceedingly rare and is considered one of the **least common genetic causes** of ambiguous genitalia in a female. - Deficiency of **aromatase** in the placenta prevents the conversion of androgens to estrogens, leading to **masculinization of a female fetus**, but this pathway is only a minor contributor to fetal androgenization. *WNT-4 gene mutation* - **WNT-4** is crucial for **female sexual differentiation** and acts as an anti-testis factor. - Mutations can lead to **Müllerian aplasia** and variable degrees of virilization in genetic females, making it a recognized, though not the most common, cause of ambiguous genitalia. *Congenital adrenal hyperplasia* - This is the **most common cause** of ambiguous genitalia in a female, primarily due to **21-hydroxylase deficiency**. - Excess adrenal androgens lead to **virilization** of the external genitalia in genetic females. *Maternal androgen exposure* - Virilization can occur from **maternal sources** such as androgen-secreting tumors, exogenous androgen use, or aromatase inhibitors during pregnancy. - This is an **uncommon but recognized cause**, more frequent than aromatase deficiency but far less common than CAH. *Fetal placental steroid sulfatase deficiency* - This deficiency typically results in **low maternal estrogen levels** and can cause **placental insufficiency** and abnormalities in labor, but it does **not directly cause ambiguous genitalia** in a female fetus. - While it affects steroid metabolism, it does not lead to the accumulation of androgens necessary for virilization of female external genitalia.

Question 5: All are features of Osteogenesis imperfecta except-

A. Multiple fractures
B. Blue sclera
C. Hearing loss
D. Cataract (Correct Answer)
E. Dentinogenesis imperfecta

Explanation: ***Cataract*** - **Cataracts** are not typically associated with **osteogenesis imperfecta (OI)**. Ocular manifestations in OI predominantly involve the sclera. - While other connective tissue disorders might feature cataracts, they are not a characteristic diagnostic or common finding in OI. *Multiple fractures* - **Multiple fractures** with minimal or no trauma are a hallmark of **osteogenesis imperfecta**, due to defective **type I collagen** synthesis. - The severity and frequency of these fractures vary depending on the specific type of OI. *Blue sclera* - **Blue sclera** is a classic feature of **osteogenesis imperfecta**, caused by the underlying choroidal veins showing through a thinned, translucent sclera due to defective **collagen**. - This is a key diagnostic clue, often present from birth or early childhood. *Hearing loss* - **Hearing loss** is common in **osteogenesis imperfecta**, particularly the **conductive type**, but can also be sensorineural or mixed. - It results from **ossicular chain abnormalities**, otosclerosis, or fragility of the middle ear bones, all related to the collagen defect. *Dentinogenesis imperfecta* - **Dentinogenesis imperfecta** is a characteristic dental manifestation of **osteogenesis imperfecta**, seen in approximately 50% of cases. - It involves defective dentin formation leading to discolored (gray, blue, or brown), translucent teeth that are prone to wear and fracture due to the same collagen defect affecting bones.

Question 6: A 10-year-old male child presented with complaints of severe progressive weakness of bilateral lower limbs, imbalance in walking, and slurred speech for the past 3 years, with recent development of visual disturbance, behavioral symptoms, and rapid progression of motor weakness. MRI was performed at the time of presentation. What is the diagnosis?

A. X-linked adrenoleukodystrophy (Correct Answer)
B. Alexander's disease
C. Krabbe's disease
D. Metachromatic leukodystrophy
E. Canavan disease

Explanation: ***X-linked adrenoleukodystrophy*** - This condition presents in males, typically between ages 4 and 10 years, with progressive neurological deterioration including **motor weakness**, **ataxia**, **visual disturbances**, and **behavioral changes**, consistent with the patient's symptoms. - The disease involves demyelination in the central nervous system due to the accumulation of **very long-chain fatty acids (VLCFAs)** and is inherited in an **X-linked recessive pattern**. *Alexander's disease* - This typically presents in infancy or early childhood with **megalencephaly**, developmental delay, and seizures, which are not described in this patient. - MRI often shows characteristic frontal white matter changes and **periventricular rim enhancement**. *Krabbe's disease* - This is an autosomal recessive disorder that usually presents in infants, with irritability, feeding difficulties, and rapid neurodegeneration, leading to **severe developmental regression**. - It involves the accumulation of **galactocerebroside** in neural tissues due to **beta-galactocerebrosidase deficiency**. *Metachromatic leukodystrophy* - This is an autosomal recessive lysosomal storage disorder that can present in late infancy, juvenile, or adult forms with progressive **demyelination** and neurological deficits. - While it causes **motor weakness** and cognitive decline, it often involves **peripheral neuropathy** and is characterized by the accumulation of **sulfatides**, not VLCFAs. *Canavan disease* - This is an autosomal recessive disorder caused by **aspartoacylase deficiency** leading to accumulation of **N-acetylaspartic acid (NAA)**. - Typically presents in early infancy (3-6 months) with **hypotonia**, **macrocephaly**, and **severe developmental delay**, earlier than the presentation in this case. - MRI shows diffuse white matter changes with characteristic involvement of subcortical U-fibers.

Question 7: X-linked disease leading to intellectual disability is -

A. Tuberous sclerosis
B. Phenylketonuria
C. Myotonic dystrophy
D. Fragile-X syndrome (Correct Answer)
E. Down syndrome

Explanation: ***Fragile-X syndrome*** - This is the most common inherited cause of **intellectual disability** and is inherited in an **X-linked dominant pattern**. - It is caused by an expansion of a **CGG trinucleotide repeat** in the *FMR1* gene on the X chromosome. *Down syndrome* - This is a **chromosomal disorder** (trisomy 21), not X-linked. - It is the most common **genetic cause** of intellectual disability overall, resulting from an extra copy of chromosome 21. *Tuberous sclerosis* - This is an **autosomal dominant** disorder, not X-linked. - It involves the growth of **benign tumors** in various organs, including the brain, skin, kidneys, and heart. *Phenylketonuria* - This is an **autosomal recessive** metabolic disorder, not X-linked. - It results from a deficiency of the enzyme **phenylalanine hydroxylase**, leading to a buildup of phenylalanine. *Myotonic dystrophy* - This is an **autosomal dominant** disorder, not X-linked. - It is characterized by progressive **muscle wasting** and **myotonia** (delayed muscle relaxation).

Question 8: A male child with Fanconi syndrome with nephrocalcinosis has a variant of dent disease. All are true except :

A. Proteinuria
B. Rickets
C. Hypercalciuria
D. Similar presentation in father (Correct Answer)
E. Progressive chronic kidney disease

Explanation: ***Similar presentation in father*** - Dent disease is an **X-linked recessive disorder** primarily affecting males due to mutations in the *CLCN5* or *OCRL1* genes. - While the father carries the Y chromosome and does not have the gene mutation, the mother is an asymptomatic carrier, passing the disease-causing allele to her sons. - **The father cannot present with the same X-linked condition** as he passes only his Y chromosome to male offspring. *Proteinuria* - **Low molecular weight proteinuria** is a hallmark of Dent disease and Fanconi syndrome, resulting from impaired reabsorption in the proximal tubules. - This is a direct consequence of the tubular dysfunction characteristic of these conditions. *Rickets* - **Rickets** can develop due to the renal phosphate wasting (hypophosphatemia) and vitamin D abnormalities (impaired activation) seen in Dent disease and Fanconi syndrome. - These bone manifestations are common complications of chronic kidney tubule dysfunction in children. *Hypercalciuria* - **Hypercalciuria** is a primary feature of Dent disease, leading to nephrocalcinosis and nephrolithiasis. - This excessive urinary calcium excretion contributes to the formation of kidney stones and calcification of renal tissue. *Progressive chronic kidney disease* - **Progressive CKD** is a recognized long-term complication of Dent disease, with many patients developing end-stage renal disease (ESRD) by adulthood. - The chronic tubular dysfunction and recurrent nephrolithiasis contribute to progressive nephron loss over time.

Question 9: A 10-year-old child presents with fever since 24 hours. History reveals 3 episodes of chest infection and passage of bulky, foul smelling stools. The most probable diagnosis is?

A. Cystic fibrosis (Correct Answer)
B. Crigler-Najjar syndrome
C. Maple syrup urine disease
D. Bilirubin conjugation defect
E. Shwachman-Diamond syndrome

Explanation: ***Cystic fibrosis*** - This genetic disorder causes defective **chloride transport**, leading to thick secretions in various organs, including the lungs and pancreas. - Recurrent **chest infections** are due to thick mucus trapping bacteria in the airways, and **bulky, foul-smelling stools** result from pancreatic insufficiency and malabsorption. *Crigler-Najjar syndrome* - This is a rare **genetic disorder** affecting bilirubin metabolism, leading to severe unconjugated hyperbilirubinemia. - Its primary presentation is **jaundice** and potential neurologic complications (**kernicterus**), not recurrent respiratory infections or steatorrhea. *Maple syrup urine disease* - This is an **autosomal recessive metabolic disorder** affecting the metabolism of branched-chain amino acids (leucine, isoleucine, valine). - It presents with characteristic **sweet-smelling urine** and severe neurological dysfunction, not primarily respiratory or gastrointestinal symptoms. *Bilirubin conjugation defect* - This is a broad term that can encompass several conditions like Crigler-Najjar syndrome or Gilbert's syndrome, all primarily presenting with **jaundice** due to impaired bilirubin processing. - It does not explain the recurrent chest infections or malabsorptive stools described in the child. *Shwachman-Diamond syndrome* - This is a rare **autosomal recessive disorder** featuring bone marrow dysfunction, pancreatic insufficiency, and skeletal abnormalities. - While it can cause malabsorption and increased infection risk due to **neutropenia**, the pattern of recurrent chest infections with steatorrhea is more classic for cystic fibrosis, which has a higher prevalence.

Question 10: All of the following are seen in Fragile X syndrome except:

A. Autism
B. Female preponderance (Correct Answer)
C. Cardiac murmurs
D. Mental retardation
E. Macro-orchidism

Explanation: ***Female preponderance*** - **Fragile X syndrome** primarily affects males more severely due to it being an **X-linked dominant inheritance pattern** with variable expression and penetrance. - While females can be carriers or mildly affected, the full syndrome with significant intellectual disability and physical features is much more common in males. *Autism* - **Autistic-like behaviors** and **autism spectrum disorder** are frequently observed in individuals with Fragile X syndrome. - This is a common **neurodevelopmental comorbidity** associated with the genetic mutation. *Cardiac murmurs* - **Mitral valve prolapse (MVP)** is a common cardiac anomaly found in individuals with Fragile X syndrome, which can present as a **cardiac murmur**. - This is one of the associated physical features of the syndrome, likely due to connective tissue abnormalities. *Mental retardation* - **Intellectual disability**, ranging from mild to severe, is a **hallmark feature** of Fragile X syndrome. - It is the **most common inherited cause of intellectual disability**. *Macro-orchidism* - **Post-pubertal macroorchidism** (enlarged testicles) is seen in approximately **80% of adult males** with Fragile X syndrome. - This is one of the characteristic **physical features** associated with the condition.

Question 11: Acrodermatitis enteropathica is:-

A. Inherited disorder of impaired uptake of zinc from body (Correct Answer)
B. Inherited disorder of excessive excretion of zinc from body
C. Inherited disorder of excessive excretion of copper from body
D. Inherited disorder of impaired uptake of copper from body
E. Inherited disorder of impaired excretion of zinc from body

Explanation: ***Inherited disorder of impaired uptake of zinc from body*** - **Acrodermatitis enteropathica** is an **autosomal recessive** genetic disorder characterized by a mutation in the **SLC39A4 gene**, which encodes a zinc transporter protein (ZIP4). - This mutation leads to **impaired absorption of dietary zinc** in the intestine, resulting in severe **zinc deficiency**. - Clinical features include **periorificial and acral dermatitis**, **diarrhea**, and **alopecia** that respond to zinc supplementation. *Inherited disorder of excessive excretion of zinc from body* - This statement is incorrect as Acrodermatitis enteropathica is due to **impaired uptake**, not excessive excretion of zinc. - Excessive excretion of zinc is not the mechanism responsible for the primary deficiency seen in this condition. *Inherited disorder of excessive excretion of copper from body* - This describes conditions like **Wilson's disease**, which involves copper accumulation due to impaired biliary excretion, not zinc deficiency. - Acrodermatitis enteropathica specifically relates to **zinc metabolism**, not copper. *Inherited disorder of impaired uptake of copper from body* - This describes conditions like **Menkes disease**, a rare X-linked recessive disorder characterized by a defect in copper transport and absorption, leading to copper deficiency. - Acrodermatitis enteropathica is distinctly a **zinc metabolism disorder**. *Inherited disorder of impaired excretion of zinc from body* - This would imply zinc accumulation rather than deficiency, which is not the pathophysiology of Acrodermatitis enteropathica. - The condition is characterized by **zinc deficiency due to malabsorption**, not problems with zinc excretion.

Question 12: An 8 year old boy complains of increasing muscle weakness. On examination, his calves are bulky and show muscle tightening. His serum creatine kinase levels are increasing with age. Which of the following is the most likely diagnosis?

A. Congenital myopathy
B. Dystrophin deficiency (Correct Answer)
C. Myelin deficiency
D. Hereditary sensorimotor neuropathy
E. Becker muscular dystrophy

Explanation: ***Dystrophin deficiency*** - The presentation of an 8-year-old boy with **increasing muscle weakness**, **bulky calves** (pseudohypertrophy), and **elevated creatine kinase** is highly characteristic of Duchenne muscular dystrophy, which is caused by a dystrophin deficiency. - The muscle tightening and progressive increase in **creatine kinase** over time further support this diagnosis, as muscle breakdown leads to enzyme release. - Duchenne typically presents between **3-5 years** with progressive weakness, wheelchair dependence by early teens, and very high CK levels (10-100x normal). *Becker muscular dystrophy* - While also caused by **dystrophin deficiency** (partial rather than complete), Becker muscular dystrophy has a **later onset** (usually age 10-15 years) and **milder, slower progression**. - The age of 8 years with significant symptoms and the rapid progression described are more consistent with **Duchenne** than Becker. *Congenital myopathy* - While hereditary muscle disorders, congenital myopathies typically present at birth or in early infancy with **generalized hypotonia** and **muscle weakness**, often static or slowly progressive. - They usually do not exhibit the prominent calf pseudohypertrophy seen in Duchenne muscular dystrophy. *Myelin deficiency* - Myelin deficiency disorders primarily affect the **nervous system**, leading to issues with nerve signal transmission rather than direct muscle weakness and pseudohypertrophy. - Symptoms would typically include **neurological deficits** such as sensory loss, ataxia, or spasticity. *Hereditary sensorimotor neuropathy* - These neuropathies (e.g., Charcot-Marie-Tooth disease) involve both **sensory and motor nerves**, leading to muscle weakness, atrophy, and sensory loss, often in the distal limbs. - They do not typically cause **calf pseudohypertrophy** or progressively high creatine kinase levels as seen in primary muscle diseases.

Question 13: Ataxia telangiectasia is associated with all of the following except:

A. Insulin resistance
B. Increased fraction of IgA immunoglobulins (Correct Answer)
C. Recurrent sinopulmonary infections
D. Lymphatic reticular malignancies
E. Decreased alpha-fetoprotein levels

Explanation: ***Increased fraction of IgA immunoglobulins*** - Ataxia-telangiectasia is characterized by **decreased or absent IgA** and **low IgG2 and IgE** levels, leading to immunodeficiency. - The deficiency in IgA contributes to the recurrent sinopulmonary infections often seen in affected individuals. *Insulin resistance* - **Insulin resistance** is a known endocrine manifestation in patients with Ataxia-telangiectasia, often developing later in the disease course. - This is linked to the broader cellular dysfunction caused by the **ATM gene mutation**, which affects processes like DNA repair and cell cycle control. *Recurrent sinopulmonary infections* - Due to the associated **immunodeficiency**, particularly **IgA deficiency**, patients with Ataxia-telangiectasia are highly susceptible to recurrent sinopulmonary infections. - These infections, including **pneumonia and sinusitis**, are a significant cause of morbidity and mortality. *Lymphatic reticular malignancies* - Patients with Ataxia-telangiectasia have a significantly **increased risk of developing various cancers**, particularly **leukemias and lymphomas**. - This predisposition to malignancy is attributed to the defective **ATM gene**, which impairs DNA repair mechanisms and promotes genomic instability. *Decreased alpha-fetoprotein levels* - Ataxia-telangiectasia is actually associated with **elevated alpha-fetoprotein (AFP)** levels, not decreased levels. - **Elevated serum AFP** is a characteristic laboratory finding in A-T and serves as a useful diagnostic marker, though the mechanism is not fully understood.

Question 14: 10-year old male with poor growth, poor appetite, recurrent chest infection and steatorrhea is likely to have ____________ .

A. Mental retardation
B. Recurrent skin allergy
C. Diabetes mellitus
D. High sodium and chloride levels in the sweat (Correct Answer)
E. Celiac disease

Explanation: ***High sodium and chloride levels in the sweat*** - The constellation of poor growth, poor appetite, recurrent chest infections, and **steatorrhea** in a child is highly suggestive of **cystic fibrosis (CF)**. - **Cystic fibrosis** is characterized by defective chloride transport, leading to thick, viscous secretions in various exocrine glands, and the diagnostic hallmark is elevated **sweat chloride levels**. *Mental retardation* - While some genetic disorders causing poor growth might be associated with mental retardation, it does not directly explain **recurrent chest infections** or **steatorrhea**. - There is no direct link between mental retardation and the specific exocrine dysfunction seen in this patient's symptoms. *Recurrent skin allergy* - **Recurrent skin allergies** would present with dermatological symptoms like rash, itching, or eczema, which are not mentioned in the patient's primary complaints. - Skin allergies do not account for **poor growth**, **steatorrhea**, or frequent lung infections. *Diabetes mellitus* - **Diabetes mellitus** in children usually presents with symptoms like polyuria, polydipsia, unexplained weight loss, and fatigue, not typically recurrent chest infections or steatorrhea. - Although CF can lead to **CF-related diabetes** later in life due to pancreatic dysfunction, it's not the initial presenting symptom that encompasses all features described here. *Celiac disease* - **Celiac disease** can present with steatorrhea and poor growth due to malabsorption, but it does not typically cause **recurrent chest infections**. - The respiratory symptoms are the key distinguishing feature pointing toward cystic fibrosis rather than a purely gastrointestinal malabsorption disorder.

Question 15: Which of the following syndromes is associated with mental retardation?

A. Morquio syndrome B
B. Natowicz syndrome
C. Hunter syndrome (Correct Answer)
D. Sly syndrome
E. Scheie syndrome

Explanation: ***Hunter syndrome*** - Hunter syndrome (Mucopolysaccharidosis Type II) is an X-linked recessive disorder characterized by the lysosomal accumulation of **glycosaminoglycans** (dermatan sulfate and heparan sulfate). - It leads to a range of symptoms including coarse facial features, skeletal abnormalities, and **developmental delay** or **intellectual disability** in more severe forms. *Morquio syndrome B* - **Morquio syndrome B** (MPS IVB) is a lysosomal storage disorder caused by a deficiency of the enzyme **beta-galactosidase**. - While it causes skeletal abnormalities and corneal clouding, it is generally **not associated with intellectual disability**. *Natowicz syndrome* - **Natowicz syndrome** is a rare genetic disorder characterized by **spastic paraplegia** and other neurological symptoms. - It is not typically cited as a syndrome primarily associated with widespread mental retardation as a core feature. *Scheie syndrome* - **Scheie syndrome** (Mucopolysaccharidosis Type IS) is a lysosomal storage disorder caused by **alpha-L-iduronidase deficiency**. - It is the mildest form of MPS I and typically presents with skeletal abnormalities, corneal clouding, and cardiac involvement, but **intelligence is usually normal**. *Sly syndrome* - **Sly syndrome** (Mucopolysaccharidosis Type VII) is a rare lysosomal storage disorder caused by a deficiency in **beta-glucuronidase**. - While patients can have skeletal abnormalities and organomegaly, the presence and severity of **intellectual disability are variable** and generally less consistent or severe than in Hunter syndrome.

Question 16: A 7-year-old boy has demineralized bones with pseudofractures. Physiologic doses of vitamin D do not result in improvement. Which of the following is most likely to be associated with this syndrome?

A. alopecia
B. low 1,25(OH)2 vitamin D levels (Correct Answer)
C. osteoporosis
D. hyperphosphatemia
E. elevated parathyroid hormone (PTH)

Explanation: ***low 1,25(OH)2 vitamin D levels*** - The described condition is suggestive of rickets due to **vitamin D-dependent rickets type I** (VDDR-I) or **II (VDDR-II)**, where the body either cannot convert 25-hydroxyvitamin D to its active form (1,25(OH)2D) or has resistance to its effects. - In VDDR-I, there is a deficiency in the enzyme **1-alpha-hydroxylase**, leading to **low levels of active vitamin D** despite sufficient precursor (25-hydroxyvitamin D). *alopecia* - While alopecia can be associated with **vitamin D-dependent rickets type II** (VDDR-II), it is not a universal finding and is more specific to defects in the **vitamin D receptor (VDR)**, rather than just the general presentation of demineralized bones and pseudofractures. - The question describes general features of rickets resistant to physiologic vitamin D doses and doesn't provide enough information to specifically pinpoint VDDR-II over VDDR-I. *osteoporosis* - **Osteoporosis** is characterized by reduced bone mass and structural deterioration, making bones fragile and prone to fractures. - The primary issue here is **demineralization (osteomalacia/rickets)** due to impaired vitamin D metabolism, not primarily a qualitative bone matrix defect as seen in osteoporosis. *hyperphosphatemia* - In rickets due to vitamin D deficiency or resistance, **hypophosphatemia** is typically observed. - **Vitamin D** plays a crucial role in regulating calcium and phosphate absorption from the gut and reabsorption in the kidneys, and its deficiency or impaired action leads to low serum phosphate levels. *elevated parathyroid hormone (PTH)* - While **elevated PTH** is indeed found in vitamin D-dependent rickets due to **secondary hyperparathyroidism** (the body's response to hypocalcemia), it is a **consequence** of the underlying vitamin D deficiency or resistance. - The question asks what is "most likely to be associated with this syndrome," and **low 1,25(OH)2 vitamin D levels** is the **primary pathophysiologic defect** in VDDR-I, making it the more direct and specific answer.

Question 17: 4 year old male, recurrent URTI, has difficulty breathing, High arched palate, Failure to grow and impaired hearing, management is

A. Airway management and feeding support
B. Genetic testing for syndromes
C. Speech and language therapy
D. Referral to ENT and geneticist (Correct Answer)
E. Prophylactic antibiotics and immunization

Explanation: ***Referral to ENT and geneticist*** - The constellation of **recurrent URTI**, **high-arched palate**, **failure to grow**, and **impaired hearing** in a 4-year-old child suggests a potential underlying craniofacial anomaly or genetic syndrome. - A **geneticist** can help diagnose underlying genetic conditions, while an **ENT specialist** can address the recurrent upper respiratory tract infections and impaired hearing, which could be related to conditions like **cleft palate** or **CHARGE syndrome**. - This is the **most appropriate initial step** for comprehensive evaluation and diagnosis. *Airway management and feeding support* - While important for immediate stabilization in some cases, these are *supportive measures* that might be necessary *after* a diagnosis is established or to manage acute crises. - They do not address the primary investigation and diagnosis of the complex symptoms presented. *Genetic testing for syndromes* - This is an integral part of the diagnostic process for many syndromes. - However, it's typically performed *after* an initial evaluation by a geneticist and often requires specific indications or panel choices based on clinical findings, rather than being the first and sole management step. *Speech and language therapy* - This is a crucial intervention if speech and language development is affected, which is likely given the impaired hearing and potential palate issues. - However, it addresses a symptom rather than the underlying cause and isn't the initial step for diagnosis or comprehensive management. *Prophylactic antibiotics and immunization* - While recurrent URTIs may warrant consideration of prophylactic measures, this approach treats symptoms without addressing the underlying cause. - Appropriate immunization should already be part of routine care, and prophylactic antibiotics don't address the structural and genetic issues causing the clinical presentation.

Question 18: Streak ovaries are seen in: CMC (Vellore) 09

A. Turner syndrome (Correct Answer)
B. Down syndrome
C. Klinefelter syndrome
D. Kallmann syndrome
E. Swyer syndrome

Explanation: ***Turner syndrome*** - Females with **Turner syndrome** (45, XO) often have underdeveloped, non-functional **streak ovaries** due to accelerated germ cell atresia. - This leads to **primary amenorrhea** and **infertility** due to **gonadal dysgenesis**. *Down syndrome* - **Down syndrome** (trisomy 21) is characterized by specific facial features, intellectual disability, and congenital heart defects. - While it can affect various organ systems, it is **not typically associated** with streak ovaries. *Klinefelter syndrome* - **Klinefelter syndrome** (47, XXY) affects males, leading to hypogonadism, infertility, and often gynecomastia. - It involves **testicular dysgenesis**, not ovarian abnormalities. *Kallmann syndrome* - **Kallmann syndrome** is a genetic condition characterized by **hypogonadotropic hypogonadism** (impaired production of GnRH) and **anosmia** (inability to smell). - It does not involve structural ovarian abnormalities like streak ovaries but rather a deficiency in hormonal stimulation. *Swyer syndrome* - **Swyer syndrome** (46, XY complete gonadal dysgenesis) also presents with streak gonads, but affected individuals have a **female phenotype with XY karyotype**. - Unlike Turner syndrome, these individuals have **normal stature** and lack the somatic features of Turner syndrome.

Question 19: Wilms' tumor associated with all except -

A. Beckwith Weidman
B. Denys-Drash syndrome
C. Digeorge syndrome (Correct Answer)
D. WAGR
E. Perlman syndrome

Explanation: ***Digeorge syndrome*** - **DiGeorge syndrome** is a genetic disorder associated with T-cell immunodeficiency, hypocalcemia, and **congenital heart defects**, but *not* primarily with Wilms' tumor. - It results from a deletion on **chromosome 22q11.2**, leading to abnormal development of the third and fourth pharyngeal pouches. *Beckwith-Wiedemann syndrome* - **Beckwith-Wiedemann syndrome** is closely associated with an increased risk of **Wilms' tumor**, often presenting with macrosomia, macroglossia, and omphalocele. - It is linked to abnormalities on **chromosome 11p15.5**, affecting growth regulation. *Denys-Drash syndrome* - **Denys-Drash syndrome** is characterized by the triad of **Wilms' tumor**, **diffuse mesangial sclerosis** (leading to renal failure), and male **pseudohermaphroditism**. - It is caused by mutations in the **WT1 gene**. *WAGR syndrome* - **WAGR syndrome** is an acronym for **W**ilms' tumor, **A**niridia, **G**enitourinary anomalies, and **R**ange of developmental delays. - This syndrome is caused by a deletion on **chromosome 11p13**, encompassing both the **PAX6** and **WT1** genes. *Perlman syndrome* - **Perlman syndrome** is a rare overgrowth disorder associated with an increased risk of **Wilms' tumor**, presenting with macrosomia, visceromegaly, and distinctive facial features. - It is caused by mutations in the **DIS3L2 gene** on chromosome 2q37.

Question 20: A 6 year old male child presented with deterioration of renal functions. On examination, he is mentally retarded and has got athetosis. There are multiple healed wounds on his body. His mother reassures you that it was as a result of self inflicted injuries. USG showed bilateral renal calculi. Which of the following statements is FALSE regarding the above mentioned condition?

A. Allopurinol may be used in treating the condition
B. Kelley - Seegmiller syndrome is a milder variant of the condition
C. Hyperuricemia is a characteristic feature of the condition
D. It is an autosomal recessive condition (Correct Answer)
E. HGPRT enzyme deficiency is the underlying biochemical defect

Explanation: ***It is an autosomal recessive condition*** - **Lesch-Nyhan syndrome** is an **X-linked recessive disorder**, meaning it primarily affects males and is inherited through the mother. - The gene responsible for **hypoxanthine-guanine phosphoribosyltransferase (HGPRT)** deficiency is located on the X chromosome. *Allopurinol may be used in treating the condition* - **Allopurinol** can be used to treat the **hyperuricemia** and prevent **renal calculi** and **gout** in patients with Lesch-Nyhan syndrome. - It works by inhibiting **xanthine oxidase**, thereby reducing uric acid production. *Kelley - Seegmiller syndrome is a milder variant of the condition* - **Kelley-Seegmiller syndrome** is indeed a milder variant of **Lesch-Nyhan syndrome**, characterized by partial rather than complete deficiency of **HGPRT** activity. - Patients with Kelley-Seegmiller syndrome typically present with **hyperuricemia** and **gout-like symptoms** but without the severe neurological manifestations such as **cognitive impairment** and **self-mutilation**. *Hyperuricemia is a characteristic feature of the condition* - **Hyperuricemia** is a hallmark feature of **Lesch-Nyhan syndrome** due to the deficiency of **HGPRT**, leading to overproduction and decreased salvage of purines. - This elevated uric acid level can cause **gouty arthritis** and **renal calculi**, contributing to renal dysfunction. *HGPRT enzyme deficiency is the underlying biochemical defect* - **Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)** deficiency is the fundamental enzyme defect in **Lesch-Nyhan syndrome**. - This enzyme is crucial for the **purine salvage pathway**, and its absence leads to overproduction of uric acid and accumulation of purine precursors that contribute to the neurological manifestations.

Question 21: Which of the following is not a feature of Turner's syndrome?

A. Bicuspid aortic valve
B. External genitalia are normal
C. Swelling of nape of neck
D. Tall stature (Correct Answer)
E. Cubitus valgus

Explanation: ***Tall stature*** - **Tall stature** is a feature of conditions like **Klinefelter syndrome** (XXY), not Turner syndrome. - Individuals with Turner syndrome (monosomy X) typically present with **short stature**, which is one of the most consistent clinical features. *Bicuspid aortic valve* - A **bicuspid aortic valve** is a common cardiovascular anomaly found in individuals with Turner syndrome. - This congenital heart defect can lead to complications such as **aortic stenosis** or **aortic regurgitation**. *External genitalia are normal* - The **external genitalia** of individuals with Turner syndrome are typically **normal** and female in appearance at birth. - However, they experience **gonadal dysgenesis** (streaky ovaries), leading to primary amenorrhea and infertility. *Swelling of nape of neck* - **Swelling of the nape of the neck** is characteristic of Turner syndrome, often presenting as **nuchal folds** or a **webbed neck**. - This is due to **lymphatic malformation** during fetal development. *Cubitus valgus* - **Cubitus valgus** (increased carrying angle of the elbow) is a common skeletal abnormality in Turner syndrome. - This results from abnormal bone development and is present in approximately 50% of individuals with Turner syndrome.

Question 22: A baby boy is brought to the hospital because of convulsions. In the course of workup, his body temperature and plasma glucose are normal, but his CSF glucose is 12 mg/dL. A possible explanation is:

A. GLUT-1 45K deficiency in microglia
B. GLUT 5 deficiency in cerebral capillaries
C. SGLT 1 deficiency in astrocytes
D. GLUT-1 55K deficiency in capillaries (Correct Answer)
E. GLUT-3 deficiency in neurons

Explanation: ***GLUT-1 55K deficiency in capillaries*** - A CSF glucose of 12 mg/dL with normal plasma glucose strongly suggests a problem with **glucose transport across the blood-brain barrier (BBB)**. - The **GLUT-1 isoform (55K)** is the primary glucose transporter responsible for moving glucose from the blood into the brain across the **endothelial cells of the capillaries**, and its deficiency leads to profoundly low CSF glucose, causing seizures. *GLUT-1 45K deficiency in microglia* - The **GLUT-1 45K isoform** is found primarily on **astrocytes** and **neurons** in the brain, and while critical for neuronal glucose uptake, its deficiency alone would not cause such a profound drop in CSF glucose unless the 55K isoform in capillaries was also affected. - **Microglia** primarily express GLUT-5 and GLUT-3, but their function is not the primary determinant of CSF glucose levels. *GLUT 5 deficiency in cerebral capillaries* - **GLUT-5** is primarily a **fructose transporter** and is not the main glucose transporter in the brain or at the blood-brain barrier. - Its deficiency would not significantly impact **glucose transport** into the CSF. *GLUT-3 deficiency in neurons* - **GLUT-3** is the primary neuronal glucose transporter and is critical for neuronal metabolism. - However, GLUT-3 deficiency would affect **intracellular neuronal glucose uptake** rather than glucose transport across the BBB, so CSF glucose levels would remain normal while neurons might be energy-deprived. - The key finding of **low CSF glucose** indicates a problem at the **capillary level** (BBB), not at the neuronal uptake level. *SGLT 1 deficiency in astrocytes* - **SGLT1 (Sodium-Glucose Linked Transporter 1)** is an active glucose transporter primarily found in the **intestine** and **kidney**, and in some cells of the brain but not as the primary glucose transporter for the BBB. - Astrocytes primarily use **GLUT-1 (45K isoform)** for glucose uptake, not SGLT1, or for transport across capillaries.

Question 23: A 3 year old child develops headaches and is brought to the family doctor. Funduscopic examination reveals papilledema; one retina also shows a very vascular tumor. CT of the head demonstrates a cystic tumor of the cerebellum. This child has a high likelihood of later developing which of the following?

A. Pheochromocytoma
B. Pancreatic neuroendocrine tumor
C. Bilateral renal cell carcinoma (Correct Answer)
D. Hemangioblastoma of the spinal cord
E. Acoustic neuroma

Explanation: ***Bilateral renal cell carcinoma*** - The presentation of a **cerebellar cystic tumor** with **retinal hemangioblastoma** (vascular tumor) is highly suggestive of **Von Hippel-Lindau (VHL) disease**. - **VHL disease** is an autosomal dominant disorder that significantly increases the risk of developing **bilateral renal cell carcinoma**, which is a common and serious manifestation. - Renal cell carcinoma occurs in approximately **70% of VHL patients** and is a leading cause of mortality, making surveillance critical. *Pheochromocytoma* - While **pheochromocytomas** can be associated with VHL disease (10-20% of cases), they are less common than renal cell carcinoma and typically present with symptoms of catecholamine excess, which are not mentioned here. - VHL disease primarily involves a wide range of tumors, with **renal cell carcinoma** being a major concern later in life for affected individuals. *Pancreatic neuroendocrine tumor* - **Pancreatic neuroendocrine tumors** are also a recognized feature of VHL syndrome but are less common and typically present later in adulthood. - The most significant life-threatening concern in children and young adults with VHL is often the development of **renal cell carcinoma** and central nervous system hemangioblastomas. *Hemangioblastoma of the spinal cord* - **Spinal cord hemangioblastomas** are indeed part of the VHL disease spectrum (25% of cases), but this option lists another manifestation of VHL, whereas the question asks for a high likelihood of *later* developing *which of the following*, implying a major associated systemic malignancy often seen in VHL patients. - While spinal cord hemangioblastomas are common, **renal cell carcinoma** is a major systemic malignancy that poses a significant long-term risk for VHL patients and is often the focus of surveillance. *Acoustic neuroma* - **Acoustic neuromas** (vestibular schwannomas) are **NOT associated with VHL disease**; they are a hallmark feature of **Neurofibromatosis Type 2 (NF2)**, not VHL. - VHL is characterized by hemangioblastomas (CNS and retina), renal cell carcinoma, pheochromocytomas, and pancreatic tumors—not schwannomas.

Question 24: A 22-year-old primigravida notes absent fetal movement for 2 days. The fetus is delivered stillborn at 19 weeks' gestation. The macerated fetus shows marked hydrops fetalis and a large posterior cystic hygroma of the neck. At autopsy, internal anomalies include aortic coarctation and a horseshoe kidney. Which of the following karyotypes is most likely to be present in cells obtained from this fetus?

A. 47, XYY
B. 45, X (Correct Answer)
C. 47, XX, +18
D. 47, XX, +21
E. 47, XXY

Explanation: ***45, X*** - The combination of **hydrops fetalis**, a large **cystic hygroma**, **aortic coarctation**, and **horseshoe kidney** is highly characteristic of **Turner syndrome (45, X)**. - Turner syndrome is caused by the **absence of an entire X chromosome** in females and often leads to severe developmental anomalies, frequently resulting in stillbirth. *47, XYY* - This karyotype describes **XYY syndrome (Jacob's syndrome)** in males, characterized by an **extra Y chromosome**. - It typically presents with tall stature and normal development, but not the severe fetal anomalies seen in this case. *47, XXY* - This karyotype describes **Klinefelter syndrome** in males, characterized by an **extra X chromosome**. - It typically presents with tall stature, infertility, gynecomastia, and learning difficulties, but not the severe fetal anomalies or early lethality seen in this case. *47, XX, +18* - This karyotype indicates **Trisomy 18 (Edwards syndrome)**, which is associated with various severe congenital malformations. - While some features like **intrauterine growth restriction** and heart defects can be seen, the specific combination of **cystic hygroma** and **aortic coarctation** with hydrops is less classic for Trisomy 18. *47, XX, +21* - This karyotype represents **Trisomy 21 (Down syndrome)**, which is characterized by intellectual disability, distinctive facial features, and cardiac defects. - **Hydrops fetalis** and **cystic hygroma** are rare in Down syndrome, making it an unlikely diagnosis given the complete clinical picture.

Question 25: Which of the following is a feature of Phenylketonuria?

A. Loss of deep tendon reflexes
B. All of the options
C. Macrocephaly
D. Intellectual disability (Correct Answer)
E. Seizures

Explanation: ***Intellectual disability*** - Unmanaged **phenylketonuria (PKU)** leads to a toxic buildup of **phenylalanine** in the brain, causing severe and irreversible **intellectual disability**. - This neurotoxic effect is the primary and most devastating long-term consequence if not diagnosed and treated early. *Seizures* - While seizures can occur in **untreated PKU** due to neurotoxicity, they are a less consistent feature compared to intellectual disability. - Seizures typically occur in the context of severe, untreated disease and are considered a complication rather than a defining diagnostic feature. - Intellectual disability is the more universal and characteristic neuropsychiatric manifestation of PKU. *Loss of deep tendon reflexes* - This is not a typical feature of PKU; patients usually present with **increased muscle tone** and **hyperreflexia** due to neurological damage. - Loss of deep tendon reflexes is more characteristic of certain peripheral neuropathies or disorders affecting lower motor neurons. *Macrocephaly* - **Microcephaly**, rather than macrocephaly, can occasionally be observed in severe, untreated PKU due to impaired brain growth. - Macrocephaly is generally associated with conditions like hydrocephalus or certain genetic syndromes, not PKU. *All of the options* - This option is incorrect because the loss of deep tendon reflexes and macrocephaly are not characteristic features of PKU. - While seizures can occur, intellectual disability is the most defining and consistent feature among the options provided.

Question 26: What is the typical IQ range for males affected with Fragile X syndrome?

A. IQ range of 20-40
B. IQ range of 60-80 (Correct Answer)
C. IQ range of 80-100
D. Normal IQ range (90-110)
E. IQ range of 50-70

Explanation: **IQ range of 60-80** - Males affected with **Fragile X syndrome** typically experience **moderate intellectual disability**, corresponding to an IQ range of 60-80. - This range indicates significant cognitive impairment, yet usually allows for some level of independent living and vocational skills with support. *IQ range of 20-40* - An IQ range of 20-40 represents **severe intellectual disability**, which is less common for the typical presentation of Fragile X syndrome in males. - While some individuals with Fragile X may fall into this range, it is not considered the most typical or average outcome. *IQ range of 50-70* - An IQ range of 50-70 represents **mild to moderate intellectual disability**, which overlaps with but is generally slightly lower than the most typical presentation. - While many males with Fragile X syndrome may score in this range, the typical range cited in literature extends slightly higher to 60-80. *IQ range of 80-100* - An IQ range of 80-100 is considered **borderline to low-average intelligence**, which is generally higher than the typical impact of Fragile X syndrome on male cognitive function. - This range is not indicative of the moderate intellectual disability characteristic of the syndrome. *Normal IQ range (90-110)* - A **normal IQ range (90-110)** is inconsistent with the diagnosis of Fragile X syndrome, which is a leading cause of inherited intellectual disability. - While females with Fragile X may have a wider range of IQs, including normal intelligence, males are typically more severely affected.

Question 27: Which of the following is true about ataxia telangiectasia?

A. There is absence of amphicytes in different organs
B. It is an autosomal recessive disease (Correct Answer)
C. It is associated with normal immune function
D. Serum levels of IgA are increased
E. Serum alpha-fetoprotein levels are decreased

Explanation: ***It is an autosomal recessive disease*** - Ataxia telangiectasia is caused by mutations in the **ATM gene**, which is inherited in an **autosomal recessive** pattern. - This genetic defect leads to a deficiency in a protein crucial for DNA repair, causing systemic effects. *There is absence of amphicytes in different organs* - This statement is incorrect; **ataxia telangiectasia** is not characterized by an absence of amphicytes. - The term "amphicytes" is not typically associated with the defining pathological features of ataxia telangiectasia. *It is associated with normal immune function* - Ataxia telangiectasia is associated with **immunodeficiency**, particularly affecting T- and B-cell function. - Patients often experience recurrent infections due to impaired adaptive immunity, which is not a characteristic of normal immune function. *Serum levels of IgA are increased* - Patients with ataxia telangiectasia typically have **decreased serum levels of IgA**, and often IgG and IgE, leading to immunodeficiency. - Increased IgA levels are characteristic of other conditions and not ataxia telangiectasia. *Serum alpha-fetoprotein levels are decreased* - In ataxia telangiectasia, serum **alpha-fetoprotein (AFP) levels are characteristically elevated**, not decreased. - Elevated AFP is a useful diagnostic marker for this condition.

Question 28: An 8-month-old infant is brought in with poor feeding, lethargy, hypotonia, and hepatomegaly. Labs reveal hypoglycemia and metabolic acidosis. Which condition is most likely?

A. Hereditary fructose intolerance
B. Galactosemia
C. Pompe disease
D. Von Gierke disease (Correct Answer)
E. Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency

Explanation: ***Von Gierke disease*** - **Type I glycogen storage disease** (GSD I) typically presents in infancy with **hypoglycemia** (due to impaired glucose release from glycogen), **hepatomegaly** (due to glycogen accumulation), and **lactic acidosis**. - Other common findings include **hyperlipidemia** and **hyperuricemia**, while **hypotonia** and **poor feeding** are generalized symptoms stemming from metabolic derangements. *Hereditary fructose intolerance* - This condition presents when **fructose** is introduced into the diet, typically after 4-6 months of age, with symptoms like **nausea, vomiting, abdominal pain**, and **hepatomegaly**. - While it can cause **hypoglycemia** and **metabolic acidosis**, the profound **hypotonia** and general metabolic collapse described in an 8-month-old on a typical diet makes GSD I more likely initially. *Galactosemia* - Symptoms usually appear within days or weeks of birth upon the initiation of **milk feeding**, including **vomiting, lethargy, poor feeding, jaundice, hepatomegaly**, and **cataracts**. - While it causes **hypoglycemia** and can lead to acidosis and hypotonia, the age of presentation and lack of specific mention of jaundice or cataracts makes it a less precise fit. *Pompe disease* - Also known as **glycogen storage disease type II**, it is characterized by the accumulation of glycogen in **lysosomes**, primarily affecting muscles. - The infantile form presents with severe **cardiomyopathy**, **muscle weakness**, and **hypotonia**, but **hypoglycemia** and **hepatomegaly** are not its primary or most prominent features. *Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency* - A **fatty acid oxidation disorder** that presents with episodic **hypoglycemia** (particularly during fasting or illness), **lethargy**, and **hepatomegaly**. - Key distinguishing features include **hypoketotic hypoglycemia** and elevated **dicarboxylic acids** on urine organic acids, but the **lactic acidosis** and overall metabolic profile are more consistent with GSD I.

Question 29: A 3-year-old presents with recurrent respiratory infections, failure to thrive, and greasy stools. Sweat chloride is 95 mEq/L. Which gene is mutated?

A. JAK3
B. BTK
C. CFTR (Correct Answer)
D. FOXP3
E. ATM

Explanation: ***CFTR*** - The patient's symptoms (recurrent respiratory infections, failure to thrive, greasy stools) combined with a **sweat chloride of 95 mEq/L** are classic for **cystic fibrosis**. - **Cystic fibrosis** is caused by a mutation in the **Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene**, which encodes a chloride channel. *JAK3* - Mutations in **JAK3** are associated with **severe combined immunodeficiency (SCID)**, characterized by profound immune dysfunction. - While recurrent infections occur, the full constellation of symptoms including pulmonary, pancreatic, and elevated sweat chloride points away from JAK3-SCID. *BTK* - The **BTK gene** is associated with **X-linked agammaglobulinemia (Bruton's agammaglobulinemia)**, leading to recurrent bacterial infections due to absent B cells and immunoglobulins. - This condition does not typically cause the lung disease, pancreatic insufficiency, or elevated sweat chloride seen in cystic fibrosis. *FOXP3* - Mutations in **FOXP3** cause **IPEX (Immunodysregulation, Polyendocrinopathy, Enteropathy, X-linked) syndrome**, characterized by severe autoimmune disease, often involving enteropathy, endocrinopathy, and eczema. - While some gastrointestinal issues may be present, it does not typically cause recurrent respiratory infections, the specific type of lung disease, or the characteristic high sweat chloride observed. *ATM* - The **ATM gene** is mutated in **ataxia-telangiectasia**, which presents with progressive cerebellar ataxia, telangiectasias, immunodeficiency, and increased cancer risk. - While patients may have recurrent respiratory infections due to immunodeficiency, they do not present with pancreatic insufficiency, greasy stools, or the pathognomonic elevated sweat chloride test that definitively points to cystic fibrosis.

Question 30: A 6-year-old presents with developmental delay, musty body odor, and fair skin. Lab tests show high phenylalanine levels. What is the most appropriate management?

A. Low-phenylalanine diet (Correct Answer)
B. Avoidance of ascorbic acid
C. Vitamin D supplementation
D. High-protein diet
E. Tetrahydrobiopterin (BH4) supplementation

Explanation: ***Low-phenylalanine diet*** - The patient's symptoms (developmental delay, musty body odor, fair skin) and high **phenylalanine levels** are classic for **phenylketonuria (PKU)**. - Management primarily involves a strict **low-phenylalanine diet** to prevent further neurological damage. - This is the **cornerstone of PKU management** and must be initiated as early as possible. *Tetrahydrobiopterin (BH4) supplementation* - While **BH4 (sapropterin)** can be beneficial in some patients with **BH4-responsive PKU** (a subset of PKU cases), it is not first-line management. - BH4 testing is performed after diagnosis, but dietary restriction remains the primary treatment. - Not all PKU patients respond to BH4, and it's used as an adjunct, not a replacement for dietary management. *Avoidance of ascorbic acid* - **Ascorbic acid** (vitamin C) is generally not contraindicated in PKU and does not impact phenylalanine metabolism. - This intervention is not relevant to the management of PKU. *Vitamin D supplementation* - While vitamin D supplementation might be necessary for general health, especially in children with restricted diets, it is not the primary treatment for **phenylketonuria (PKU)**. - It does not directly address the elevated phenylalanine levels. *High-protein diet* - A **high-protein diet** would exacerbate the condition, as proteins are a major source of phenylalanine. - This would lead to even higher phenylalanine levels and worsen the symptoms of PKU.

Question 31: Which of the following is TRUE about Turner Syndrome?

A. Increased risk of breast cancer
B. Webbed neck (Correct Answer)
C. Normal menstruation
D. Tall stature
E. Intellectual disability is universal

Explanation: ***Webbed neck*** - A **webbed neck** (pterygium colli) is a characteristic physical feature seen in individuals with **Turner Syndrome**, caused by abnormal lymphatic development during fetal life. - This is one of several **dysmorphic features** commonly associated with the 45,X karyotype. *Increased risk of breast cancer* - Individuals with **Turner Syndrome** generally have a **reduced risk of breast cancer** due to hypogonadism and lower estrogen exposure. - Breast development is often incomplete or absent due to **gonadal dysgenesis**. *Normal menstruation* - Individuals with **Turner Syndrome** typically experience **primary amenorrhea** (absence of menstruation) due to **gonadal dysgenesis** and failure of ovarian development. - They lack functioning ovaries and therefore do not produce adequate **sex hormones** for menstrual cycles. *Tall stature* - Individuals with **Turner Syndrome** typically have **short stature** as a defining feature, often requiring growth hormone therapy. - The absence of one X chromosome affects genes involved in **linear bone growth**. *Intellectual disability is universal* - Individuals with **Turner Syndrome** typically have **normal intelligence**, though some may experience specific learning difficulties in visuospatial processing and mathematics. - Unlike some other chromosomal disorders, **intellectual disability is not a typical feature** of Turner Syndrome.

Question 32: Which diagnostic tool is preferred for metabolic disease screening in children?

A. Urinalysis
B. Genetic testing
C. Complete Blood count
D. Tandem mass spectrometry (Correct Answer)
E. Plasma amino acid analysis

Explanation: ***Tandem mass spectrometry*** - **Tandem mass spectrometry (TMS)** is the preferred method for newborn screening of many **inborn errors of metabolism** because it can simultaneously detect a wide range of metabolites from a single dried blood spot. - This technique rapidly identifies multiple **amino acid disorders**, **fatty acid oxidation disorders**, and **organic acidemias**, allowing for early intervention. *Urinalysis* - While urinalysis can detect some metabolic abnormalities (e.g., **ketones**, **glucose**), it is not a comprehensive screening tool for the broad spectrum of inherited metabolic diseases. - It primarily identifies end-products of metabolism rather than specific enzyme deficiencies or precursor compounds. *Genetic testing* - **Genetic testing** is highly specific for known genetic mutations, but it is typically used for confirmatory diagnosis or targeted screening when a specific condition is suspected, not for broad, universal newborn metabolic screening. - It can be expensive and time-consuming for population-wide screening of hundreds of potential metabolic disorders. *Complete Blood count* - A **complete blood count (CBC)** assesses cellular components of the blood (e.g., **red blood cells**, **white blood cells**, **platelets**) and is useful for detecting hematological disorders. - It does not directly screen for metabolic diseases, although some metabolic disorders can secondarily affect blood cell counts. *Plasma amino acid analysis* - **Plasma amino acid analysis** can detect specific aminoacidopathies (e.g., **phenylketonuria**, **maple syrup urine disease**), but it is limited to amino acid disorders only. - Unlike tandem mass spectrometry, it cannot simultaneously screen for fatty acid oxidation disorders and organic acidemias, making it less comprehensive for broad metabolic screening.

Question 33: A 6-month-old child presents with jaundice, hepatomegaly, and cataracts. What is the most likely diagnosis?

A. Fructose intolerance
B. Hemochromatosis
C. Glycogen storage disease
D. Galactosemia (Correct Answer)
E. Wilson disease

Explanation: ***Galactosemia*** - **Galactosemia** is a genetic disorder affecting galactose metabolism, leading to a build-up of galactose-1-phosphate in tissues. - Symptoms like **jaundice**, **hepatomegaly**, and **cataracts** in an infant are classic presentations, often exacerbated by milk (lactose/galactose) intake. *Fructose intolerance* - **Hereditary fructose intolerance** typically manifests after the introduction of fructose into the diet, causing symptoms like vomiting, hypoglycemia, and liver dysfunction. - While it can cause hepatomegaly and jaundice, **cataracts** are not a typical feature of fructose intolerance. *Hemochromatosis* - **Hemochromatosis** is a disorder of iron overload, usually presenting in adulthood with symptoms such as fatigue, joint pain, liver disease (cirrhosis), and diabetes. - It is rarely diagnosed in infancy and **cataracts** are not a characteristic symptom. *Glycogen storage disease* - **Glycogen storage diseases** involve defects in glycogen synthesis or breakdown, leading to various symptoms depending on the specific enzyme deficiency. - Types affecting the liver often cause **hepatomegaly** and **hypoglycemia**, but **cataracts** are not a common, primary feature in most forms, and jaundice is also less typical than in galactosemia. *Wilson disease* - **Wilson disease** is a copper metabolism disorder that causes liver disease and neuropsychiatric symptoms. - It typically presents later in childhood or adolescence (rarely before age 3), and while it causes hepatomegaly and jaundice, the ocular finding is **Kayser-Fleischer rings**, not cataracts.

Question 34: What are the implications of early newborn screening for homocystinuria on intervention strategies?

A. Outcomes are similar regardless of screening.
B. Early detection enables dietary management and prevents serious complications. (Correct Answer)
C. Genetic testing is not necessary if symptoms are absent.
D. Screening has minimal impact on long-term outcomes.
E. Treatment can be delayed until clinical symptoms appear.

Explanation: ***Early detection enables dietary management and prevents serious complications.*** - Early newborn screening allows for the timely initiation of **dietary modification**, specifically a **low-methionine diet** and **pyridoxine (vitamin B6) supplementation**, which are crucial for managing homocystinuria. - This proactive intervention can prevent severe, irreversible complications such as **intellectual disability**, **thromboembolic events**, **ectopia lentis**, and **skeletal abnormalities**. *Outcomes are similar regardless of screening.* - This statement is incorrect because delaying diagnosis and treatment of homocystinuria can lead to **progressive and irreversible damage**, significantly worsening patient outcomes. - Without early intervention, individuals with homocystinuria often experience severe neurological, ocular, and vascular complications that impact their **quality of life and longevity**. *Genetic testing is not necessary if symptoms are absent.* - While symptoms may not be present in the neonatal period, homocystinuria is a **genetic disorder** with a progressive course, meaning symptoms will eventually develop without intervention. - **Newborn screening** aims to identify affected individuals *before* symptom onset, allowing for preventative treatment and thus making genetic testing and early diagnosis critical even in asymptomatic newborns. *Screening has minimal impact on long-term outcomes.* - This is false, as early screening and subsequent treatment for homocystinuria have a **profound positive impact** on long-term outcomes, dramatically improving cognitive development and reducing the risk of life-threatening complications. - The goal of newborn screening programs for metabolic disorders like homocystinuria is precisely to **mitigate long-term morbidity and mortality** through early intervention. *Treatment can be delayed until clinical symptoms appear.* - This is incorrect because by the time clinical symptoms of homocystinuria manifest (typically including developmental delays, lens dislocation, or thrombotic events), **irreversible damage** has often already occurred. - The **critical window** for preventing neurological and vascular complications is in the neonatal period, before symptoms develop, which is why newborn screening and immediate dietary intervention are essential. - Delaying treatment until symptom onset defeats the primary purpose of screening programs and results in significantly **worse neurodevelopmental outcomes**.

Question 35: A 10-year-old child presents with a history of recurrent fractures, blue sclerae, and early-onset hearing loss. What is the most likely diagnosis?

A. Osteogenesis imperfecta (Correct Answer)
B. Ehlers-Danlos syndrome
C. Marfan syndrome
D. Achondroplasia
E. Hypophosphatasia

Explanation: ***Osteogenesis imperfecta*** - The classic triad of **recurrent fractures**, **blue sclerae**, and **early-onset hearing loss** is highly indicative of osteogenesis imperfecta. - This condition is caused by a genetic defect in **type I collagen synthesis**, leading to brittle bones. *Ehlers-Danlos syndrome* - Characterized primarily by **joint hypermobility**, skin hyperextensibility, and tissue fragility. - While some types can involve skeletal issues, **recurrent fractures** and **blue sclerae** are not distinguishing features. *Marfan syndrome* - Manifests with tall stature, **arachnodactyly**, lens luxation, and cardiovascular abnormalities like **aortic root dilation**. - **Recurrent fractures** and **blue sclerae** are not typical findings in Marfan syndrome. *Achondroplasia* - This is a form of **short-limbed dwarfism** due to a defect in endochondral ossification, specifically impacting cartilage formation. - Key features include short stature, a large head, and a prominent forehead, but it does not typically present with **blue sclerae** or **recurrent fractures** from fragile bones. *Hypophosphatasia* - A metabolic bone disease with deficiency of alkaline phosphatase leading to defective bone mineralization. - Can present with fractures and skeletal deformities but typically lacks **blue sclerae** and **hearing loss**, which are pathognomonic for osteogenesis imperfecta.

Question 36: A child presents with multiple bone fractures over the past year with minimal trauma. Which condition should be evaluated as a potential cause?

A. Osteogenesis imperfecta (Correct Answer)
B. Rickets
C. Normal childhood activity
D. Non-accidental trauma
E. Scurvy

Explanation: ***Osteogenesis imperfecta*** - This condition is characterized by **brittle bones** that fracture easily with **minimal or no trauma**, consistent with the child's presentation. - It is a genetic disorder affecting **collagen formation**, leading to defective bone matrix. *Rickets* - Rickets is a condition caused by a deficiency of **vitamin D, calcium, or phosphate**, leading to **softening and weakening of bones**. - While it can cause bone pain and deformities, **multiple fractures from minimal trauma** are less characteristic compared to osteogenesis imperfecta. *Scurvy* - **Vitamin C deficiency** can cause skeletal abnormalities and bone fragility due to impaired collagen synthesis. - However, scurvy is **extremely rare** in developed countries and typically presents with other signs like **gingival bleeding, petechiae, and poor wound healing**. *Normal childhood activity* - While children are prone to **minor injuries and fractures**, "multiple bone fractures over the past year with minimal trauma" goes beyond what is considered normal. - This pattern strongly suggests an **underlying pathological condition** rather than typical accidents. *Non-accidental trauma* - **Child abuse** can certainly cause multiple fractures, and it should always be considered in cases of unexplained or suspicious injuries. - However, the question specifically asks for a "condition" that should be evaluated as a "potential cause," focusing on **medical diagnoses** rather than external injury mechanisms, making osteogenesis imperfecta a more direct answer in this context.

Question 37: A child presents with recurrent respiratory infections and a sweat chloride test result of 60 mmol/L. What is the most appropriate next step?

A. Repeat the sweat chloride test
B. Start prophylactic antibiotics
C. Genetic testing for cystic fibrosis (Correct Answer)
D. Chest X-ray and pulmonary function tests
E. Sputum culture for bacterial pathogens

Explanation: ***Genetic testing for cystic fibrosis*** - A sweat chloride test result of 60 mmol/L is in the **intermediate range** (typically 40-59 mmol/L for infants and 40-60 mmol/L for older children/adults being indeterminate) and, combined with recurrent respiratory infections, strongly suggests **cystic fibrosis (CF)**. - **Genetic testing for CFTR mutations** is the definitive diagnostic step when sweat chloride results are borderline or indicative of CF, confirming the diagnosis and guiding specific treatment strategies. *Repeat the sweat chloride test* - While it might be tempting to repeat a borderline test, the current result of 60 mmol/L, especially with suggestive clinical symptoms, warrants a more definitive diagnostic test immediately. - Repeating the test would delay the diagnosis and would likely yield a similar result, still requiring a confirmatory test. *Start prophylactic antibiotics* - Prophylactic antibiotics are a management strategy for patients with confirmed cystic fibrosis, but initiating them before a definitive diagnosis is premature. - The immediate priority is to confirm the underlying cause of the recurrent infections. *Chest X-ray and pulmonary function tests* - These tests are valuable for assessing the _extent_ of lung damage and _monitoring disease progression_ in a patient with recurrent respiratory infections. - However, they do not establish the underlying diagnosis of cystic fibrosis, which is crucial for appropriate long-term management. *Sputum culture for bacterial pathogens* - While sputum culture is useful for identifying specific pathogens in CF patients and guiding antibiotic therapy, it does not establish the underlying diagnosis. - This would be more appropriate after confirming CF diagnosis to guide targeted antimicrobial treatment for acute exacerbations.

Question 38: Which of the following is a key characteristic of Turner syndrome?

A. Webbed neck (Correct Answer)
B. Tall stature
C. Macrocephaly
D. Gynecomastia
E. Normal fertility

Explanation: ***Webbed neck*** - A **webbed neck** is a classic physical feature of Turner syndrome, caused by abnormalities in lymphatic development during fetal life. - This condition results from an **X chromosome monosomy** (45,XO) and is associated with various other developmental anomalies. *Tall stature* - Individuals with Turner syndrome typically present with **short stature**, a common and defining feature, rather than tall stature. - This is partly due to the absence of the **SHOX gene** on the missing X chromosome, which is critical for bone growth. *Macrocephaly* - **Macrocephaly** (abnormally large head) is not a characteristic feature of Turner syndrome; head circumference is usually within the normal range. - While some genetic conditions can cause macrocephaly, Turner syndrome primarily affects skeletal and reproductive development. *Gynecomastia* - **Gynecomastia** is the development of breast tissue in males and is not associated with Turner syndrome, which affects females. - Females with Turner syndrome often experience **gonadal dysgenesis**, leading to absent or underdeveloped ovaries and lack of female secondary sexual characteristics. *Normal fertility* - **Infertility** is a hallmark feature of Turner syndrome due to **ovarian dysgenesis** and streak gonads. - Most individuals with Turner syndrome require hormone replacement therapy and assisted reproductive technologies if they wish to conceive.

Question 39: A 5-year-old boy presents with developmental delay and distinctive facial features. Genetic testing reveals a deletion on chromosome 22q11.2. What is the most likely diagnosis?

A. Down syndrome
B. Fragile X syndrome
C. DiGeorge syndrome (Correct Answer)
D. Williams syndrome
E. Prader-Willi syndrome

Explanation: ***DiGeorge syndrome*** - **DiGeorge syndrome** is caused by a **deletion on chromosome 22q11.2**, which is directly confirmed by genetic testing in this case. - This syndrome is associated with **developmental delay** and distinct **facial features**, along with other findings such as **cardiac defects**, **immune deficiencies**, and **hypocalcemia**. *Down syndrome* - **Down syndrome** is caused by **trisomy 21** (an extra copy of chromosome 21), not a deletion on chromosome 22q11.2. - While it presents with developmental delay and distinctive facial features, the **genetic finding** rules out this diagnosis. *Fragile X syndrome* - **Fragile X syndrome** is caused by a **mutation (CGG repeat expansion)** on the **FMR1 gene** on the X chromosome, not a deletion on chromosome 22q11.2. - It is a common cause of inherited intellectual disability, but the genetic test result is inconsistent. *Williams syndrome* - **Williams syndrome** is caused by a **deletion on chromosome 7q11.23**, not chromosome 22q11.2. - It also presents with developmental delay and distinctive facial features, often described as an "elfin" appearance. *Prader-Willi syndrome* - **Prader-Willi syndrome** is caused by a **deletion or uniparental disomy on chromosome 15q11-13**, not chromosome 22q11.2. - It presents with developmental delay, hypotonia, hyperphagia, and characteristic facial features, but the genetic test result is not consistent with this diagnosis.

Question 40: A 10-year-old girl presents with short stature and a webbed neck. Upon examination, she has widely spaced nipples. What is the most likely chromosomal abnormality?

A. Trisomy 21
B. Turner Syndrome (Correct Answer)
C. Klinefelter Syndrome
D. Fragile X Syndrome
E. Trisomy 18

Explanation: ***Turner Syndrome*** - **Short stature**, **webbed neck**, and widely spaced nipples are classic features of **Turner Syndrome** (45, XO). - This chromosomal abnormality results from the complete or partial **absence of an X chromosome**. *Trisomy 21* - Characterized by distinct facial features, **intellectual disability**, and congenital heart defects. - This condition is also known as **Down Syndrome**, which typically presents with an extra copy of chromosome 21. *Klinefelter Syndrome* - Affects males, characterized by an **extra X chromosome** (47, XXY), leading to **tall stature**, small testes, and gynecomastia. - Presents in males and is associated with reduced fertility. *Fragile X Syndrome* - The most common inherited cause of **intellectual disability**, primarily affecting males, and is characterized by a **long face** and **prominent ears**. - It results from a mutation in the **FMR1 gene** on the X chromosome. *Trisomy 18* - Also known as **Edwards Syndrome**, characterized by clenched fists, rocker-bottom feet, and severe intellectual disability. - Most affected infants have **congenital heart defects** and typically do not survive beyond the first year of life.

Question 41: A 10-year-old male presents with progressive weakness, difficulty climbing stairs, and a positive Gowers sign. Creatine kinase is markedly elevated, and genetic testing is positive for Duchenne muscular dystrophy. Which of the following is the most effective long-term management strategy for this condition?

A. Corticosteroids and physical therapy (Correct Answer)
B. Gene therapy and regular monitoring
C. Spinal fusion and ACE inhibitors
D. Supportive care with monitoring
E. Mechanical ventilation and wheelchair modifications

Explanation: ***Corticosteroids and physical therapy*** - **Corticosteroids** (e.g., prednisone, deflazacort) are the mainstay of treatment for Duchenne muscular dystrophy (**DMD**) as they can **slow disease progression**, preserve muscle strength, and prolong ambulation. - **Physical therapy** is crucial for maintaining muscle flexibility, preventing contractures, and optimizing functional abilities, thereby improving the **quality of life** for patients with DMD. *Gene therapy and regular monitoring* - While **gene therapy** shows promise as an emerging treatment, it is currently in **clinical trials** and not yet a widely approved or available long-term management strategy for DMD. - Regular monitoring is essential, but without an established primary treatment like corticosteroids, it alone is not the most effective long-term strategy. *Spinal fusion and ACE inhibitors* - **Spinal fusion** is a surgical intervention sometimes used to correct **severe scoliosis**, a complication of DMD, but it is not a primary long-term management strategy for the underlying muscle degeneration. - **ACE inhibitors** are used to manage cardiac complications such as **cardiomyopathy** that can develop in DMD, but they do not address the primary neuromuscular degeneration. *Supportive care with monitoring* - **Supportive care** is an important aspect of DMD management, encompassing various interventions like respiratory support and nutritional guidance. - However, without active pharmacological treatment such as corticosteroids, supportive care alone is **insufficient** to significantly alter the disease course or prolong functional independence. *Mechanical ventilation and wheelchair modifications* - **Mechanical ventilation** becomes necessary in advanced stages when respiratory muscles weaken, and **wheelchair modifications** are important for mobility as ambulation declines. - These are essential **supportive interventions** for managing complications of DMD, but they do not slow disease progression or represent the most effective long-term management strategy compared to corticosteroids and physical therapy.

Question 42: A 12-year-old girl presents with a history of short stature, delayed puberty, and learning difficulties. Physical examination reveals a high-arched palate and scoliosis. What is the most likely diagnosis?

A. Turner syndrome (Correct Answer)
B. Klinefelter syndrome
C. Noonan syndrome
D. Down syndrome
E. Fragile X syndrome

Explanation: ***Turner syndrome*** - **Short stature** and **delayed puberty** are classic features of Turner syndrome, which results from the absence of all or part of an X chromosome in females. - Other common physical findings include a **high-arched palate** and an increased risk of **scoliosis**, as described in the patient. - The combination of these features with **learning difficulties** strongly supports this diagnosis. *Klinefelter syndrome* - This condition affects **males** (XXY karyotype) and typically presents with tall stature, gynecomastia, and hypogonadism, which does not match the patient's presentation. - While learning difficulties can occur, the physical features are distinct from those described in the female patient. *Noonan syndrome* - Noonan syndrome features can overlap with Turner syndrome (e.g., short stature, delayed puberty), but it is characterized by normal chromosomes and often includes distinctive facial features, **pulmonary stenosis**, and *normal intelligence*. - The combination of **scoliosis** and **learning difficulties** makes Turner syndrome a more fitting diagnosis here. *Down syndrome* - Down syndrome is caused by trisomy 21 and is characterized by distinct facial features (**upslanting palpebral fissures**, epicanthic folds), intellectual disability, and congenital heart defects (e.g., **AV canal defect**). - While individuals with Down syndrome have developmental delays, the specific constellation of delayed puberty, short stature, and **high-arched palate** points away from this diagnosis. *Fragile X syndrome* - Fragile X syndrome is the most common inherited cause of intellectual disability and presents with learning difficulties, but affected individuals typically have **macroorchidism** (in males), long face, and large ears. - The absence of **delayed puberty** and the presence of **short stature** and **scoliosis** make Turner syndrome more likely in this female patient.

Question 43: A 6-month-old infant presents with severe hypotonia, poor feeding, and distinctive facial features, including a tented upper lip. Genetic testing reveals a deletion on chromosome 15q11-q13. What is the most likely diagnosis?

A. Williams syndrome
B. Angelman syndrome
C. Smith-Magenis syndrome
D. Prader-Willi syndrome (Correct Answer)
E. Cri-du-chat syndrome

Explanation: ***Prader-Willi syndrome*** - **Severe hypotonia** and **poor feeding** in infancy are hallmark features, often described as "floppy baby syndrome" - Distinctive facial features include **narrow forehead**, **almond-shaped eyes**, and **tented upper lip** - Caused by **paternal deletion of chromosome 15q11-q13** (or maternal uniparental disomy) - Later in childhood, develops characteristic **hyperphagia** leading to obesity, along with hypogonadism and developmental delays *Angelman syndrome* - Also involves chromosome 15q11-q13 deletion, but from the **maternal** chromosome, resulting in a completely different phenotype - Characterized by **severe developmental delay**, **absent speech**, **ataxia**, **happy demeanor** with inappropriate laughter, and **seizures** - Not typically recognized at 6 months; diagnosis usually made after 6-12 months when developmental delays become more apparent *Williams syndrome* - Caused by deletion on **chromosome 7q11.23**, not chromosome 15 - Features include **supravalvular aortic stenosis**, **"elfin" facial features** (broad forehead, short nose, full cheeks), **hypercalcemia**, and an overly friendly personality - Cardiovascular findings are a key distinguishing feature *Smith-Magenis syndrome* - Associated with deletion on **chromosome 17p11.2**, not chromosome 15 - Presents with **self-injurious behaviors**, **sleep disturbances** (inverted circadian rhythm), distinctive facial features, and intellectual disability - Behavioral phenotype is more prominent than hypotonia *Cri-du-chat syndrome* - Caused by deletion on the **short arm of chromosome 5** (5p-) - Named for the distinctive **cat-like cry** in infancy due to laryngeal abnormalities - Features include **microcephaly**, **wide-set eyes**, **low-set ears**, and severe intellectual disability

Question 44: A 4-year-old boy presents with difficulty climbing stairs and lifting objects. Laboratory tests show elevated serum creatine kinase. Which condition is most likely?

A. Duchenne Muscular Dystrophy (Correct Answer)
B. Type 2 Diabetes
C. Hypothyroidism
D. Vitamin D deficiency
E. Becker Muscular Dystrophy

Explanation: ***Duchenne Muscular Dystrophy*** - Characterized by **progressive muscle weakness** and **difficulty with activities** such as climbing stairs, typical in young males [1]. - Elevated serum **creatine kinase** levels indicate muscle damage, supporting the diagnosis of Duchenne Muscular Dystrophy [1]. *Vitamin D deficiency* - Often presents with **muscle weakness** but typically includes symptoms like **bone pain** and fractures, not specific to climbing difficulties. - Serum creatine kinase is usually **normal** in isolated vitamin D deficiency. *Hypothyroidism* - Can cause **muscle weakness and fatigue**, but it generally presents with systemic symptoms such as **weight gain** and **cold intolerance**. - Serum creatine kinase may be slightly elevated, but this is **not a primary feature** of hypothyroidism compared to muscular dystrophies. *Type 2 Diabetes* - Primarily presents with **metabolic symptoms** such as **hyperglycemia** and does not specifically cause muscle weakness in the manner described. - While patients may experience weakness or fatigue, **elevated creatine kinase** is not associated with type 2 diabetes. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1244-1245.

Question 45: A 4-year-old boy presents with short stature, coarse facial features, and developmental delay. Laboratory tests reveal elevated lysosomal enzymes. What is the most likely diagnosis?

A. Mucopolysaccharidosis (Correct Answer)
B. Glycogen storage disease
C. Phenylketonuria
D. Galactosemia
E. Congenital hypothyroidism

Explanation: ***Mucopolysaccharidosis*** - The classic triad of **short stature**, **coarse facial features**, and **developmental delay** in a young child points towards a lysosomal storage disorder. - **Elevated lysosomal enzymes** confirm a diagnosis of mucopolysaccharidosis, where deficient enzymes lead to the accumulation of glycosaminoglycans. *Glycogen storage disease* - Primarily characterized by **hypoglycemia**, enlarged liver (hepatomegaly), and muscle weakness due to impaired glycogen metabolism. - While some forms can cause growth delay, the characteristic coarse facial features and elevated lysosomal enzymes are not typical. *Phenylketonuria* - This is an **amino acid metabolism disorder** leading to the accumulation of phenylalanine. - Symptoms include severe intellectual disability, seizures, microcephaly, and a peculiar mousy odor, but not coarse facial features or elevated lysosomal enzymes. *Galactosemia* - An inherited disorder of **carbohydrate metabolism** that prevents the body from processing galactose. - Presents in infancy with feeding difficulties, lethargy, jaundice, and cataracts, and can lead to intellectual disability and liver damage if untreated, but not the specific features described. *Congenital hypothyroidism* - Can present with developmental delay, growth retardation, and coarse facial features in untreated cases. - However, **elevated lysosomal enzymes** are not a feature of hypothyroidism, and thyroid function tests would be the key diagnostic finding.

Question 46: A pediatric patient presents with an enlarged liver. A biopsy reveals PAS-positive material within the hepatocytes. Which genetic disorder is most consistent with these findings?

A. Glycogen storage disease type I (Correct Answer)
B. Wilson disease
C. Hemochromatosis
D. Alpha-1 antitrypsin deficiency
E. Gaucher disease

Explanation: ***Glycogen storage disease type I*** - An enlarged liver (hepatomegaly) and the presence of **PAS-positive material within hepatocytes** are classic findings in **glycogen storage diseases**, particularly type I (von Gierke's disease), due to the accumulation of glycogen. - This disorder is caused by a deficiency in **glucose-6-phosphatase**, leading to impaired glycogenolysis and gluconeogenesis, resulting in severe **hypoglycemia** and **lactic acidosis**. *Wilson disease* - Characterized by the accumulation of **copper** in the liver, brain, and other organs, leading to **hepatitis**, **cirrhosis**, and neurological symptoms. - Diagnosis involves **Kayser-Fleischer rings**, low ceruloplasmin levels, and high urinary copper excretion; PAS-positive material is not a primary finding. *Hemochromatosis* - Involves excessive absorption and accumulation of **iron** in various organs, most commonly the liver, heart, and pancreas, leading to **cirrhosis**, heart failure, and diabetes. - Liver biopsy would show **iron deposition** (stained with Prussian blue), not PAS-positive material. *Alpha-1 antitrypsin deficiency* - Results from a genetic defect in the production of **alpha-1 antitrypsin**, a protease inhibitor, leading to **emphysema** and **liver disease**. - Liver biopsy may show **PAS-positive, diastase-resistant globules** within hepatocytes, but the lack of diastase resistance mentioned in the question makes this less likely. *Gaucher disease* - A lysosomal storage disorder caused by **glucocerebrosidase deficiency**, leading to accumulation of glucocerebroside in macrophages (Gaucher cells). - Presents with hepatosplenomegaly, bone pain, and anemia; liver biopsy shows Gaucher cells, not PAS-positive material in hepatocytes.

Question 47: In retinoblastoma, genetic testing is important for:

A. The affected child and their siblings should be tested
B. All family members, including parents, should be tested (Correct Answer)
C. No testing is needed if the case is unilateral
D. Only the affected child needs testing
E. Testing should be delayed until the child reaches adulthood

Explanation: ***All family members, including parents, should be tested*** - **Retinoblastoma** can be an inherited condition, and genetic testing of parents can identify if they are carriers of a **RB1 gene mutation**, even if they do not have the disease themselves. - This information is crucial for assessing the risk of future children and for the screening of other family members who might unknowingly carry the mutation. *The affected child and their siblings should be tested* - While it's important to test the affected child to confirm the **genetic mutation** and the siblings to determine their risk, this option is incomplete as it misses the critical role of parental testing. - Testing only the child and siblings doesn't provide a complete picture of the familial risk and inheritance pattern, especially if neither parent expresses the disease but one is a carrier. *No testing is needed if the case is unilateral* - This statement is incorrect because even **unilateral retinoblastoma** can be caused by a **germline mutation** in the **RB1 gene** (heritable form), which can be passed on to offspring. - Approximately 15% of unilateral retinoblastoma cases are heritable, making genetic testing essential to identify at-risk family members. *Only the affected child needs testing* - Testing only the affected child provides a diagnosis for that child but fails to address the risk to other family members, including siblings and future offspring. - It does not help in identifying carriers within the family, which is vital for **genetic counseling** and early detection strategies. *Testing should be delayed until the child reaches adulthood* - This is incorrect because **early genetic testing** is critical for timely screening and management of retinoblastoma in at-risk family members. - Delaying testing could miss the opportunity for early detection in siblings or future children, where retinoblastoma typically presents in early childhood (before age 5), and early intervention is crucial for preserving vision and life.

Question 48: A 5-year-old boy presents with short stature, a webbed neck, and widely spaced nipples. What genetic condition is most likely?

A. Turner syndrome
B. Noonan syndrome (Correct Answer)
C. Down syndrome
D. Klinefelter syndrome
E. Fragile X syndrome

Explanation: ***Noonan syndrome*** - **Noonan syndrome** is an **autosomal dominant** genetic disorder that affects **both males and females** and presents with features including **short stature**, **webbed neck (pterygium colli)**, and **widely spaced nipples**. - Additional characteristic features include **pulmonic stenosis** (most common cardiac defect), **pectus excavatum or carinatum**, **cryptorchidism in males**, **low-set ears**, and **downslanting palpebral fissures**. - Unlike Turner syndrome, Noonan syndrome occurs in both sexes with a **normal karyotype** (mutations typically in the RAS-MAPK pathway, commonly PTPN11 gene). - In this case, the patient being a **5-year-old boy** makes Noonan syndrome the most likely diagnosis. *Turner syndrome* - **Turner syndrome** (45,X or other X chromosome abnormalities) presents with similar phenotypic features including **short stature**, **webbed neck**, and **widely spaced nipples**. - However, Turner syndrome affects **phenotypic females only** - individuals have female external genitalia, gonadal dysgenesis, and typically present with primary amenorrhea. - Since this patient is described as a **boy**, Turner syndrome is **not possible** as the diagnosis. *Klinefelter syndrome* - **Klinefelter syndrome** (47,XXY) affects males and is characterized by **tall stature** (not short), **hypogonadism**, **gynecomastia**, small testes, and often **infertility**. - The presented symptoms of **short stature**, webbed neck, and widely spaced nipples are not characteristic of Klinefelter syndrome. *Down syndrome* - **Down syndrome** (Trisomy 21) presents with distinctive features including **single palmar crease**, **upslanting palpebral fissures**, **epicanthic folds**, **flat facial profile**, **protruding tongue**, and intellectual disability. - While short stature can occur, **webbed neck** and **widely spaced nipples** are not characteristic features of Down syndrome. *Fragile X syndrome* - **Fragile X syndrome** is an X-linked dominant disorder caused by CGG repeat expansion in the FMR1 gene, presenting primarily with **intellectual disability**, **autism spectrum features**, and characteristic physical features. - Physical features include **long face**, **large ears**, **macroorchidism in post-pubertal males**, and **joint hypermobility**. - The triad of short stature, webbed neck, and widely spaced nipples is not characteristic of Fragile X syndrome.

Question 49: An 8-year-old child with recurrent respiratory infections and growth retardation has a sweat test showing high chloride levels. What is the likely diagnosis?

A. Primary ciliary dyskinesia
B. Asthma
C. Cystic fibrosis (Correct Answer)
D. Bronchiectasis
E. Immunodeficiency disorder

Explanation: ***Cystic fibrosis*** - The combination of **recurrent respiratory infections**, **growth retardation**, and **high chloride levels in a sweat test** is pathognomonic for cystic fibrosis. - This genetic disorder primarily affects chloride transport, leading to thick, viscous secretions that obstruct airways and impact nutrient absorption. *Primary ciliary dyskinesia* - This condition is characterized by **recurrent respiratory infections** due to dysfunctional cilia, but it does **not typically present with growth retardation** or elevated sweat chloride. - Diagnosis involves **ciliary ultrastructure analysis** or genetic testing, not a sweat test. *Asthma* - Asthma is a chronic inflammatory airway disease causing **wheezing, cough, and shortness of breath**, often triggered by allergens or exercise. - It does **not involve growth retardation or elevated sweat chloride levels**, and respiratory infections are not typically recurrent as a primary feature. *Bronchiectasis* - Bronchiectasis involves **permanent dilatation of the bronchi** due to chronic inflammation and infection, leading to recurrent respiratory infections and chronic cough. - While it can be a complication of cystic fibrosis, **isolated bronchiectasis does not explain the growth retardation or positive sweat test** in the absence of an underlying condition. *Immunodeficiency disorder* - While immunodeficiency can cause **recurrent respiratory infections** and potentially growth retardation, it does **not cause elevated sweat chloride levels**. - Diagnosis involves **immunoglobulin levels, lymphocyte counts, and specific immune function tests**, not a sweat test.

Question 50: An infant with a suspected metabolic disorder has abnormal newborn screening results. What is the most appropriate next step to confirm the diagnosis?

A. Repeat the newborn screening
B. Conduct a comprehensive metabolic panel (Correct Answer)
C. Start dietary modifications based on the most likely diagnosis
D. Obtain a detailed three-generation family history
E. Refer to genetics specialist without further testing

Explanation: ***Conduct a comprehensive metabolic panel*** - Abnormal newborn screen results for metabolic disorders are **presumptive** diagnoses and require prompt **confirmatory testing**. - A comprehensive metabolic panel, including **amino acid analysis**, **organic acid analysis**, and **acylcarnitine profile**, can pinpoint the specific metabolic defect. *Repeat the newborn screening* - While sometimes done for minor abnormalities or sample issues, repeating the newborn screen delays definitive diagnosis and intervention in cases of **significant abnormalities**. - **Confirmatory tests** provide more detailed and specific information than a repeat screen. *Start dietary modifications based on the most likely diagnosis* - Initiating dietary changes before a definitive diagnosis is made can be **harmful** if the suspected diagnosis is incorrect or if the specific metabolic pathway affected is not fully understood. - **Nutritional intervention** for metabolic disorders is often very specific and requires confirmation. *Obtain a detailed three-generation family history* - A family history is an important part of the evaluation but is **not a confirmatory diagnostic test** for a suspected metabolic disorder in an affected infant. - While it can guide further testing or provide information about inheritance patterns, it does not directly identify the metabolic abnormality. *Refer to genetics specialist without further testing* - While genetics referral is important for long-term management and counseling, it should not precede **confirmatory diagnostic testing**. - Definitive diagnosis is needed to guide immediate management and to provide the specialist with specific information for targeted counseling.

Question 51: A 6-month-old infant presents with failure to thrive and developmental delays. Serum laboratory results show elevated liver enzymes and bilirubin. What is the most likely diagnosis?

A. Biliary atresia (Correct Answer)
B. Hepatitis
C. Alpha-1 antitrypsin deficiency
D. Galactosemia
E. Wilson disease

Explanation: ***Biliary atresia*** - This is the **most likely diagnosis** in a 6-month-old infant with **failure to thrive**, **elevated liver enzymes**, and **elevated bilirubin**. - Biliary atresia presents with **progressive conjugated hyperbilirubinemia** starting in the first 2-8 weeks of life, with **persistent jaundice**, **hepatomegaly**, and eventual **cirrhosis** if untreated. - Classic triad: **jaundice**, **acholic stools**, and **dark urine**, though not all features may be explicitly reported. - The **age of presentation** (6 months) and constellation of findings make this the most characteristic diagnosis. *Alpha-1 antitrypsin deficiency* - Can cause **neonatal hepatitis syndrome** with cholestasis, elevated transaminases, and conjugated hyperbilirubinemia. - However, the presentation is typically **earlier** (within first 2 months) and many infants are **asymptomatic** or have milder disease. - More commonly associated with **emphysema in adults** rather than isolated hepatic presentation in infancy. *Hepatitis* - Viral hepatitis can cause **elevated liver enzymes** and **bilirubin**. - However, isolated viral hepatitis as the primary cause of **chronic failure to thrive** and **developmental delays** over 6 months is less likely than structural/metabolic causes. - Would typically have more **acute presentation** or history of exposure. *Galactosemia* - Presents with **vomiting**, **jaundice**, **hepatomegaly**, **cataracts**, and **E. coli sepsis** in neonates. - Symptoms appear within **days to weeks of birth** upon initiation of milk feeding, not at 6 months. - Would be detected earlier through **newborn screening** in most developed countries. *Wilson disease* - Typically presents in **older children** (>5 years) and **adolescents**, not at 6 months. - Characterized by **copper accumulation** causing hepatic and neurological symptoms, **Kayser-Fleischer rings**. - Age of presentation makes this diagnosis extremely unlikely.

Question 52: Which genetic disorder is characterized by a deletion on chromosome 22 and includes features such as thymic hypoplasia and hypocalcemia?

A. Down syndrome
B. Turner syndrome
C. DiGeorge syndrome (Correct Answer)
D. Klinefelter syndrome
E. Williams syndrome

Explanation: ***DiGeorge syndrome*** - This syndrome is characterized by a **microdeletion on chromosome 22q11.2**, leading to developmental abnormalities. - Key features include **thymic hypoplasia ( T-cell immunodeficiency )**, **parathyroid hypoplasia (hypocalcemia)**, **congenital heart defects**, and distinctive facial features. *Down syndrome* - Caused by an extra copy of **chromosome 21 (trisomy 21)**, not a deletion on chromosome 22. - Characterized by intellectual disability, characteristic facial features, and increased risk of **congenital heart disease** and **leukemia**, not specifically thymic hypoplasia or hypocalcemia. *Turner syndrome* - Results from the absence of all or part of one **X chromosome (45, X0)**, affecting only females. - Presents with short stature, webbed neck, and **gonadal dysgenesis**, without the characteristic features of DiGeorge syndrome. *Klinefelter syndrome* - Characterized by an extra **X chromosome in males (47, XXY)**. - Typically presents with **infertility**, small testes, and gynecomastia, without a deletion on chromosome 22 or the specific clinical features mentioned. *Williams syndrome* - Caused by a **microdeletion on chromosome 7q11.23**, not chromosome 22. - Features include distinctive **"elfin" facial features**, **supravalvular aortic stenosis**, hypercalcemia (not hypocalcemia), and an overly friendly personality, without thymic hypoplasia.

Question 53: Identify the best treatment to prevent complications in a newborn diagnosed with phenylketonuria (PKU).

A. Low-phenylalanine diet (Correct Answer)
B. High-protein diet
C. Gluten-free diet
D. Ketogenic diet
E. Enzyme replacement therapy

Explanation: ***Low-phenylalanine diet*** - PKU is caused by a deficiency in the enzyme **phenylalanine hydroxylase**, leading to a buildup of **phenylalanine** in the blood. - A **low-phenylalanine diet** restricts the intake of this amino acid, preventing its accumulation and subsequent neurotoxic effects, thus averting severe complications like **intellectual disability** and seizures. *High-protein diet* - A high-protein diet would be detrimental for a newborn with PKU as it would significantly **increase phenylalanine intake**, exacerbating the metabolic disorder. - High protein intake would lead to greater accumulation of **phenylalanine**, resulting in more severe neurological damage. *Gluten-free diet* - A gluten-free diet is indicated for conditions like **celiac disease** or **gluten sensitivity**, which are unrelated to the metabolic defect in PKU. - While some dietary restrictions may overlap, a gluten-free diet does not specifically address the **phenylalanine metabolism** issue in PKU. *Ketogenic diet* - A ketogenic diet is typically used to manage certain types of **epilepsy** or metabolic disorders involving carbohydrate metabolism. - It does not directly target the **phenylalanine accumulation** that is central to PKU pathophysiology and would not be an effective primary treatment. *Enzyme replacement therapy* - While enzyme replacement therapy is effective for some metabolic disorders (e.g., **Gaucher disease**, **Fabry disease**), it is not the standard treatment for PKU. - The primary management of PKU relies on **dietary restriction** of phenylalanine rather than enzyme supplementation, though pegvaliase (an enzyme substitution therapy) may be used in some adult cases with uncontrolled phenylalanine levels.

Question 54: A 5-year-old girl presents with new-onset seizures, developmental delay, and hypopigmented macules on the skin. What is the most likely diagnosis?

A. Tuberous sclerosis (Correct Answer)
B. Neurofibromatosis type 1
C. Sturge-Weber syndrome
D. Von Hippel-Lindau disease
E. Rett syndrome

Explanation: ***Tuberous sclerosis*** - The classic triad of **seizures**, **developmental delay**, and **hypopigmented macules** (ash-leaf spots) is highly characteristic of tuberous sclerosis complex (TSC). - TSC is a **neurocutaneous disorder** with multisystem involvement, including brain tumors (subependymal giant cell astrocytomas), renal angiomyolipomas, and cardiac rhabdomyomas. *Neurofibromatosis type 1* - Characterized by **café-au-lait spots**, **axillary/inguinal freckling**, and **neurofibromas**. - While seizures and developmental delay can occur, **hypopigmented macules** are not a primary dermatological feature. *Sturge-Weber syndrome* - Identified by a characteristic **port-wine stain** (facial cutaneous angioma) in the distribution of the trigeminal nerve. - Associated with **leptomeningeal angiomas** (leading to seizures) and **ocular abnormalities** like glaucoma, but not hypopigmented macules. *Von Hippel-Lindau disease* - A rare genetic disorder predisposing to tumors in multiple organs, including **hemangioblastomas** of the central nervous system and retina, and **renal cell carcinoma**. - It does not typically present with skin lesions, seizures, or developmental delay in the same way as TSC. *Rett syndrome* - An X-linked genetic disorder causing **developmental regression** (especially loss of purposeful hand movements) and **seizures**, primarily affecting females. - However, it does not present with the characteristic **hypopigmented macules** seen in TSC, and regression typically begins after 6-18 months of normal development.

Question 55: What does the acronym LAHSAL represent in the context of congenital malformations?

A. Congenital malformation of the Hard and Soft palate
B. Congenital malformation of the Lip
C. Congenital malformation of the Alveolus
D. None of the options
E. Lip, Alveolus, Hard palate, Soft palate, and Alveolus-Lip classification (Correct Answer)

Explanation: ***Lip, Alveolus, Hard palate, Soft palate, and Alveolus-Lip classification*** - LAHSAL is an acronym derived from **L**ip, **A**lveolus, **H**ard palate, **S**oft palate, and **AL** (representing the combined Alveolus-Lip region). - This classification system provides a **comprehensive framework** for describing the **complete spectrum of cleft lip and palate deformities**. - The acronym aids clinicians in **systematically documenting** which anatomical structures are involved in the cleft malformation. *Congenital malformation of the Hard and Soft palate* - While hard and soft palate are included in LAHSAL (H and S), this option is **incomplete** as it omits the lip and alveolus components. - LAHSAL represents a **more comprehensive classification** than palatal involvement alone. *Congenital malformation of the Alveolus* - The alveolus (A) is one component of LAHSAL, but this option represents only a **partial aspect** of the full classification. - Isolated alveolar clefts are less common than combined defects. *Congenital malformation of the Lip* - The lip (L) is the first component of LAHSAL, but this option is **incomplete** as it doesn't capture the full acronym's scope. - **Isolated cleft lip** is common, but LAHSAL encompasses the entire cleft spectrum. *None of the options* - This is incorrect as LAHSAL has a specific, well-defined meaning in **cleft lip and palate classification**. - Understanding LAHSAL is fundamental in **plastic and reconstructive surgery**.

Question 56: What is the current term used to refer to Down syndrome?

A. Oligophrenia
B. Trisomy 21 (Correct Answer)
C. Mental retardation
D. Intellectual disability
E. Mongolism

Explanation: ***Trisomy 21*** - This is the **current scientific and cytogenetic term** for Down syndrome, indicating the presence of an **extra copy of chromosome 21**. - It is the most accurate and precise term describing the **genetic basis** of the condition and is universally used in medical literature. - While "Down syndrome" remains the clinical name, **Trisomy 21** is the preferred term in genetic and diagnostic contexts. *Oligophrenia* - This is an **outdated and pejorative term** for intellectual disability, no longer used in medical or scientific contexts. - It was a general term for conditions with **significantly impaired intellectual development** but has been abandoned. *Mental retardation* - This term was historically used to describe conditions of cognitive impairment but has been **replaced by "intellectual disability"** due to its stigmatizing connotations. - It is **no longer acceptable** in modern medical terminology. *Intellectual disability* - This is the **current preferred term** for describing cognitive impairment, but it refers to the **functional consequence** of Down syndrome, not the condition itself. - While accurate for describing the cognitive aspects, **Trisomy 21** is the specific genetic diagnostic term. *Mongolism* - This is an **obsolete and offensive term** that was historically used for Down syndrome based on perceived facial features. - It has been completely **abandoned** due to its racist and pejorative nature and should never be used.

Question 57: Teratology is a study of

A. Congenital heart defect
B. Congenital abnormalities (Correct Answer)
C. Wounds and injuries
D. None of the options
E. Genetic inheritance patterns

Explanation: ***Congenital abnormalities*** - **Teratology** is specifically defined as the study of birth defects or congenital abnormalities. - It focuses on the causes, mechanisms, and patterns of **abnormal development** in an embryo or fetus. *Congenital heart defect* - While a **congenital heart defect** is a type of congenital abnormality, teratology encompasses all structural or functional birth defects, not just cardiac ones. - This option is too narrow, as teratology studies a broader range of developmental abnormalities affecting various organ systems. *Genetic inheritance patterns* - **Genetic inheritance patterns** refers to the study of how traits and conditions are passed from parents to offspring (e.g., autosomal dominant, recessive, X-linked). - While genetics may contribute to congenital abnormalities, teratology specifically focuses on the **development of malformations** rather than inheritance mechanisms. - This falls under the field of **genetics**, not teratology. *Wounds and injuries* - **Wounds and injuries** refer to physical trauma that occurs after birth or during development due to external forces. - These are typically acquired conditions and do not fall under the realm of **teratology**, which deals with developmental abnormalities originating during embryogenesis or fetal development. *None of the options* - This option is incorrect because "Congenital abnormalities" accurately defines the scope of study for teratology. - The term **teratology** directly derives from Greek words meaning "monster" and "study," reflecting its historical focus on severe birth defects.

Question 58: Which of the following is a condition that is not associated with Turner's syndrome?

A. Short fourth metacarpal
B. Shield chest
C. Cryptorchidism (Correct Answer)
D. Cubitus valgus
E. Webbed neck

Explanation: ***Cryptorchidism*** - **Cryptorchidism** is a condition where one or both testicles fail to descend into the scrotum, exclusively affecting males. - **Turner syndrome** is a chromosomal disorder affecting females, characterized by the absence of all or part of one X chromosome (45,XO karyotype), making cryptorchidism impossible in affected individuals. *Cubitus valgus* - **Cubitus valgus**, an increased carrying angle of the elbow, is a common musculoskeletal anomaly observed in individuals with Turner syndrome due to developmental abnormalities. - This feature is a known part of the physical phenotype associated with the **45,XO karyotype**. *Short fourth metacarpal* - A **short fourth metacarpal** is a classic skeletal manifestation of **Turner syndrome**. - This finding is often associated with other skeletal abnormalities like **short stature** and a wide carrying angle. *Shield chest* - A **shield chest** refers to a broad chest with widely spaced nipples, which is a characteristic phenotypic feature associated with **Turner syndrome**. - This is one of the many physical dysmorphic features used in the clinical diagnosis of the syndrome. *Webbed neck* - **Webbed neck** (pterygium colli) is a classic clinical feature of **Turner syndrome** caused by cystic hygroma in utero that resolves, leaving redundant skin. - This characteristic finding is part of the diagnostic phenotype along with other features like lymphedema and low posterior hairline.

Question 59: Which of the following is true regarding Turner's syndrome?

A. Conductive hearing loss
B. Autosomal recessive inheritance
C. Increased carrying angle of the elbow (cubitus valgus)
D. Monosomy of the X chromosome (Correct Answer)
E. Transmitted through maternal inheritance

Explanation: ***Monosomy of the X chromosome*** - Turner's syndrome is a **chromosomal disorder** characterized by the presence of only one complete X chromosome (45,X) in females, instead of the usual two. - This **monosomy X** is the **fundamental genetic defect** that defines Turner's syndrome and is the underlying cause of all clinical features. - This is the **most definitive answer** as it represents the core diagnostic criterion. *Conductive hearing loss* - While girls with Turner's syndrome can have hearing problems, they more commonly experience **sensorineural hearing loss** or recurrent otitis media. - Conductive hearing loss is not a primary or characteristic feature of Turner's syndrome. *Autosomal recessive inheritance* - Turner's syndrome is a **chromosomal abnormality** (monosomy X), not an autosomal recessive genetic disorder. - Its occurrence is typically **sporadic** due to nondisjunction during meiosis, not inherited in a Mendelian fashion. *Increased carrying angle of the elbow (cubitus valgus)* - Cubitus valgus **is indeed a true characteristic feature** of Turner's syndrome and is commonly seen in affected individuals. - However, while clinically important, it is a **secondary physical manifestation** resulting from the underlying chromosomal abnormality. - The **monosomy of the X chromosome is the more fundamental answer** as it is the genetic basis for all features, including cubitus valgus. *Transmitted through maternal inheritance* - Turner's syndrome occurs **sporadically** due to random nondisjunction events during gamete formation. - It is **not transmitted** through maternal or paternal inheritance patterns. - Each occurrence is typically a de novo event, not passed from parent to child.

Question 60: Which of the following is a common feature of Down's syndrome?

A. Early onset Alzheimer's disease
B. Hypotonia (Correct Answer)
C. Congenital heart defects
D. Female infertility
E. Single palmar crease

Explanation: ***Hypotonia*** - **Generalized muscle hypotonia** (floppiness) is a hallmark feature present in nearly all individuals with Down syndrome from birth, persisting into childhood and contributing to developmental delays. - This **reduced muscle tone** is universally observed and affects motor development, posture, and feeding in infants with Down syndrome. *Congenital heart defects* - **Congenital heart defects**, particularly **atrioventricular septal defects**, are very common in Down syndrome, affecting 40-60% of individuals. - While highly prevalent, these are not universally present in all cases, unlike hypotonia which is nearly always observed. *Single palmar crease* - A **single transverse palmar crease** (simian crease) is present in approximately 45% of individuals with Down syndrome. - While common, it is not universally present and can also occur in 1-2% of the general population, making it less specific than hypotonia. *Female infertility* - **Female fertility** in Down syndrome is reduced but not universally absent; some women with Down syndrome can conceive, though there is an increased risk of miscarriage and having a child with Down syndrome. - **Male infertility** is more pronounced, with most males having impaired spermatogenesis. *Early onset Alzheimer's disease* - Individuals with Down syndrome have a high risk of developing **early-onset Alzheimer's disease** due to triplication of the APP gene on chromosome 21, but this is a later-life complication, not an early or defining feature. - This **neurological complication** typically manifests in the 40s or 50s, affecting cognition and daily functioning progressively.

Question 61: Russell silver syndrome is associated with which of the following?

A. Autosomal dominant inheritance
B. X-linked recessive inheritance
C. Maternal uniparental disomy of chromosome 7 (Correct Answer)
D. Sporadic mutation in a gene
E. Paternal uniparental disomy of chromosome 15

Explanation: ***Maternal uniparental disomy of chromosome 7*** - **Russell Silver syndrome (RSS)** is most commonly associated with **maternal uniparental disomy (UPD) of chromosome 7** or abnormal methylation of chromosome 11p15.5. - UPD occurs when both copies of a chromosome come from the same parent, leading to a dosage imbalance of imprinted genes. - Maternal UPD7 accounts for approximately **10% of RSS cases**. *Autosomal dominant inheritance* - While some cases of RSS can be inherited, the most common genetic cause is **not autosomal dominant inheritance**. - Autosomal dominant conditions typically involve a mutation in a single gene on an autosome where one copy of the altered gene in each cell is sufficient to cause the disorder. *X-linked recessive inheritance* - **X-linked recessive inheritance** primarily affects males and is passed through carrier mothers, which is not characteristic of RSS. - The genetic causes of RSS are primarily related to chromosomal methylation defects or UPD, not X-linked gene mutations. *Sporadic mutation in a gene* - While **sporadic mutations** can occur in various genetic disorders, the predominant genetic mechanisms for RSS involve **epigenetic alterations** or **chromosomal abnormalities** rather than a single gene mutation. - The most common genetic cause, maternal UPD of chromosome 7, is a chromosomal event rather than a mutation in a specific gene. *Paternal uniparental disomy of chromosome 15* - **Paternal UPD15** causes **Angelman syndrome**, not Russell-Silver syndrome. - This is a different imprinting disorder that presents with developmental delay, seizures, and happy demeanor, distinct from the growth restriction and asymmetry seen in RSS.

Question 62: What is the earliest symptom of Tay-Sachs disease?

A. Bone deformation
B. Cherry-red spot on macula
C. Exaggerated startle response (Correct Answer)
D. Developmental delay or loss of previously acquired skills
E. Macrocephaly

Explanation: ***Exaggerated startle response*** - This is often the **earliest neurological symptom** observed in infants with Tay-Sachs disease, typically appearing between **3 and 6 months of age**. - Affected infants exhibit an **abnormal, exaggerated motor response** to sudden loud noises, also known as hyperacusis. *Bone deformation* - **Bone deformations** are not a characteristic or early symptom of Tay-Sachs disease, which primarily affects the **nervous system**. - Conditions like **mucopolysaccharidoses** are more commonly associated with skeletal abnormalities. *Cherry-red spot on macula* - While a **cherry-red spot** is a classic finding in Tay-Sachs, it is usually observed around **6 months of age or later** and is not typically the *earliest* symptom. - It is a significant diagnostic indicator but generally appears after the exaggerated startle response begins. *Developmental delay or loss of previously acquired skills* - **Developmental regression** and delays become evident at later stages, typically around **6 months of age**, as the disease progresses. - While a defining feature, the **exaggerated startle response** often precedes overt signs of developmental delay. *Macrocephaly* - **Enlarged head circumference** may develop in later stages of Tay-Sachs disease, typically after **6-12 months of age**. - This occurs due to accumulation of GM2 gangliosides in neurons, but is not an early presenting symptom.

Question 63: Some patients with severe forms of Idiopathic infantile hypercalcemia present with phenotypic features similar to which of the following?

A. Williams syndrome (Correct Answer)
B. Potter's syndrome
C. Angelman syndrome
D. VHL syndrome
E. Prader-Willi syndrome

Explanation: ***Williams syndrome*** - Severe forms of **Idiopathic Infantile Hypercalcemia** (IIH) are caused by mutations in the **CYP24A1 gene**, which leads to increased production of 1,25-dihydroxyvitamin D and subsequent calcium dysregulation. - The phenotypic features of severe IIH, including **facial dysmorphism (e.g., elfin facies), supravalvular aortic stenosis, and intellectual disability**, overlap significantly with those seen in Williams syndrome, which is caused by a different genetic deletion. *Potter's syndrome* - Characterized by **bilateral renal agenesis** or severe dysgenesis, leading to oligohydramnios and subsequent compressed facial features, pulmonary hypoplasia, and limb deformities. - It is primarily a consequence of **renal failure**, not calcium dysregulation or specific facial features associated with IIH. *Angelman syndrome* - A neurodevelopmental disorder caused by a deletion or mutation on **chromosome 15**, leading to severe developmental delay, intellectual disability, movement or balance disorder, and characteristic behavioral traits like frequent laughter. - It does not involve **hypercalcemia** or the specific facial and cardiovascular features seen in IIH. *VHL syndrome* - An inherited disorder caused by mutations in the **VHL tumor suppressor gene**, predisposing individuals to various tumors, including **renal cell carcinoma, pheochromocytoma, and hemangioblastomas of the brain, spinal cord, and retina**. - This syndrome is characterized by **tumor formation** and has no direct association with hypercalcemia or the phenotypic features of IIH. *Prader-Willi syndrome* - A genetic disorder caused by loss of function of genes on **chromosome 15**, characterized by **hyperphagia, obesity, hypotonia, short stature, and intellectual disability**. - Does not involve **hypercalcemia, cardiovascular abnormalities, or the elfin facies** seen in severe IIH and Williams syndrome.

Question 64: What characteristic finding of tuberous sclerosis is present at birth but not later in life?

A. Facial angiofibroma
B. Periungal fibroma
C. Renal angiomyolipoma
D. Cardiac rhabdomyoma (Correct Answer)
E. Ash-leaf spots

Explanation: ***Cardiac rhabdomyoma*** - **Cardiac rhabdomyomas** are benign cardiac tumors that are frequently present at birth in individuals with tuberous sclerosis. - While present at birth, they often **regress spontaneously** during early childhood and are typically not found later in life unless specifically looked for, differentiating them from other characteristic lesions. *Facial angiofibroma* - **Facial angiofibromas** (also known as adenoma sebaceum) usually begin to appear between 2 and 5 years of age and *increase in size and number* throughout childhood and adulthood. - They are **not typically present at birth** and are a progressive manifestation of the disease. *Periungal fibroma* - **Periungal fibromas**, or Koenen tumors, develop around or under the fingernails and toenails, and usually appear in **late childhood or adolescence**. - They are **not present at birth** and often grow larger with age. *Renal angiomyolipoma* - **Renal angiomyolipomas** are benign kidney tumors that are a common manifestation of tuberous sclerosis, but they typically develop and **grow over time**, not usually present at birth. - They can be asymptomatic but carry a risk of hemorrhage when large, and their prevalence **increases with age**. *Ash-leaf spots* - **Ash-leaf spots** (hypopigmented macules) are often present at birth and are one of the earliest cutaneous manifestations of tuberous sclerosis. - However, unlike cardiac rhabdomyomas, these lesions **persist throughout life** and do not regress, making them a permanent dermatological feature of the condition.

Question 65: Which of the following is NOT a feature of Cerebro-occulo-genital syndrome?

A. Microcephaly
B. Short stature
C. Agenesis of corpus callosum
D. Flaccid quadriplegia (Correct Answer)
E. Cataracts

Explanation: ***Flaccid quadriplegia*** - This condition is **not a typical feature** of Cerebro-oculo-genital syndrome. - While severe neurological deficits are present, patients typically present with **hypertonia and spasticity** rather than flaccid paralysis. - **Flaccid quadriplegia** is not a primary manifestation of this disorder. *Microcephaly* - **Microcephaly** is a hallmark central nervous system finding in Cerebro-oculo-genital syndrome. - It reflects impaired brain development characteristic of this disorder. *Short stature* - **Short stature** is a common growth abnormality associated with Cerebro-oculo-genital syndrome. - It is often observed due to underlying genetic defects affecting growth and development. *Agenesis of corpus callosum* - **Agenesis of the corpus callosum** is a significant structural brain anomaly frequently seen in Cerebro-oculo-genital syndrome. - This malformation contributes to the neurological dysfunction observed in affected individuals. *Cataracts* - **Cataracts** are a key ocular manifestation (the "oculo" component) of Cerebro-oculo-genital syndrome. - Ocular abnormalities including cataracts and microphthalmia are characteristic features of this condition.

Question 66: Which of the following statements is true regarding Rett Syndrome?

A. Seizures (Correct Answer)
B. Macrocephaly
C. Cardiac arrhythmia
D. Autistic behavior
E. Occurs primarily in males

Explanation: ***Seizures*** - **Seizures** are a very common symptom in Rett Syndrome, affecting 60-80% of individuals and often requiring lifelong management. - They are one of the core neurological features developing after the period of apparently normal development, typically appearing in Stage II or III. *Macrocephaly* - Children with Rett Syndrome typically exhibit **microcephaly**, not macrocephaly, as their head growth decelerates after initial normal development. - This deceleration in head growth is a key diagnostic feature, often becoming evident between 3 and 6 months of age. *Cardiac arrhythmia* - While cardiac arrhythmias including prolonged QTc intervals do occur in Rett Syndrome and contribute to risk of sudden death, they are not as uniformly present as seizures or stereotyped hand movements. - **Autonomic dysfunction** is common but cardiac arrhythmia is not the most characteristic feature compared to neurological symptoms. *Autistic behavior* - While girls with Rett Syndrome may display social withdrawal and communication deficits early in the disease course, these are part of a distinct syndrome with regression, not classic autism spectrum disorder. - The behaviors seen in Rett Syndrome, such as loss of purposeful hand use and stereotyped hand-wringing movements, differentiate it from typical ASD. *Occurs primarily in males* - Rett Syndrome occurs **almost exclusively in females** due to the X-linked dominant inheritance pattern of MECP2 mutations. - Males with MECP2 mutations typically die in infancy due to severe encephalopathy, making female predominance a hallmark of the condition.

Question 67: Which of the following is NOT a characteristic feature of DiGeorge syndrome?

A. Abnormal development of third and fourth pouches
B. Hypocalcemic tetany
C. Congenital thymic hypoplasia
D. Hypothyroidism (Correct Answer)
E. Congenital heart defects

Explanation: ***Hypothyroidism*** - **Hypothyroidism** is not a characteristic feature of **DiGeorge syndrome**; the syndrome primarily affects structures derived from the third and fourth pharyngeal pouches, which do not include the thyroid gland. - While other endocrine issues can occur, **thyroid dysfunction** is not a common or defining component of this syndrome. *Congenital thymic hypoplasia* - **Congenital thymic hypoplasia** is a hallmark of DiGeorge syndrome, leading to **T-cell immunodeficiency** due to impaired T-lymphocyte maturation. - The **thymus** is derived from the third pharyngeal pouch, and its abnormal development is central to the syndrome's pathology. *Abnormal development of third and fourth pouches* - **DiGeorge syndrome** is fundamentally caused by **abnormal development of the third and fourth pharyngeal pouches**, leading to defects in tissues derived from these structures. - This abnormal development explains the typical constellation of symptoms, including thymic and parathyroid abnormalities. *Hypocalcemic tetany* - **Hypocalcemic tetany** is a common and serious manifestation of DiGeorge syndrome due to the **hypoplasia or aplasia of the parathyroid glands**, which are derived from the third and fourth pharyngeal pouches. - Reduced **parathyroid hormone (PTH)** levels lead to **low serum calcium**, causing symptoms like muscle spasms and tetany. *Congenital heart defects* - **Congenital heart defects**, particularly **conotruncal abnormalities** such as tetralogy of Fallot, truncus arteriosus, and interrupted aortic arch, are common features of DiGeorge syndrome. - These cardiac defects result from abnormal development of the **neural crest cells** that contribute to the cardiac outflow tract and are part of the classic **CATCH-22** mnemonic (Cardiac defects, Abnormal facies, Thymic hypoplasia, Cleft palate, Hypocalcemia).

Question 68: Which of the following is not a feature of Down syndrome?

A. Hypotonia
B. Respiratory tract Infections
C. Pigmented birth marks (Correct Answer)
D. Clinodactyly
E. Single palmar crease

Explanation: ***Pigmented birth marks*** - While pigmented birthmarks can occur in anyone, they are **not a characteristic or diagnostic feature** specifically associated with Down syndrome. - The presence of pigmented birthmarks does not offer a significant clinical clue for Down syndrome diagnosis. *Clinodactyly* - **Clinodactyly**, particularly of the fifth finger (incurved little finger), is a common physical finding in individuals with Down syndrome due to an underdeveloped middle phalanx. - This is considered a **minor physical anomaly** often seen in trisomy 21. *Hypotonia* - **Generalized hypotonia (low muscle tone)** is a hallmark feature of Down syndrome, present from birth. - This contributes to challenges in motor development and can affect various organ systems. *Respiratory tract Infections* - Individuals with Down syndrome are highly susceptible to **recurrent respiratory tract infections** due to a combination of factors, including immune dysregulation, hypotonia, and structural anomalies of the airways. - This increased susceptibility is a significant cause of morbidity and mortality in this population. *Single palmar crease* - **Single palmar crease (simian crease)** is present in approximately 50% of individuals with Down syndrome, making it a **characteristic physical finding**. - This is a single transverse palmar crease instead of the typical two creases seen in the general population.

Question 69: Among the following options, what is the most common known single-factor cause of congenital anomalies?

A. Chromosomal aberrations (Correct Answer)
B. Maternal infections
C. Drugs
D. Irradiation
E. Multifactorial inheritance

Explanation: ***Chromosomal aberrations*** - Chromosomal abnormalities, such as **aneuploidies** and **structural rearrangements**, are the most frequent single-factor cause of **congenital anomalies**, accounting for a significant proportion of birth defects. - Examples include **Down syndrome** (trisomy 21), **Turner syndrome** (XO), and **Klinefelter syndrome** (XXY), which lead to distinct clinical presentations and developmental issues. *Maternal infections* - While maternal infections like **TORCH infections (Toxoplasmosis, Other [syphilis, varicella-zoster, parvovirus B19], Rubella, Cytomegalovirus, and Herpes simplex virus)** can cause congenital anomalies, they represent a smaller proportion of overall birth defects compared to chromosomal aberrations. - The type of anomaly depends on the specific pathogen and the timing of infection during gestation. *Drugs* - **Teratogenic drugs**, such as **thalidomide** or **valproic acid**, can cause severe congenital anomalies, but they are responsible for a relatively small percentage of all birth defects. - The impact depends on the drug, dose, and the stage of fetal development during exposure. *Irradiation* - **Ionizing radiation exposure** during pregnancy, especially during critical periods of organogenesis, can lead to congenital anomalies, developmental delays, and other adverse outcomes. - However, significant teratogenic exposure to radiation is **uncommon** in most populations, making it a less frequent cause compared to other factors. *Multifactorial inheritance* - **Multifactorial disorders** result from the interaction of multiple genes and environmental factors, accounting for the **majority** of congenital anomalies overall (e.g., neural tube defects, cleft lip/palate, congenital heart defects). - However, the question asks for **single-factor** causes, and multifactorial conditions by definition involve multiple contributing factors, not a single identifiable cause.

Question 70: Chloride level in sweat is used in the diagnosis of which disease?

A. Phenylketonuria
B. Cystic fibrosis (Correct Answer)
C. Gaucher's disease
D. Osteogenesis imperfecta
E. Tay-Sachs disease

Explanation: ***Cystic fibrosis*** - **Cystic fibrosis** is characterized by a defect in the **CFTR protein**, leading to impaired chloride transport in epithelial cells. - This defect results in abnormally high salt content in sweat, making the **sweat chloride test** the gold standard for diagnosis. *Phenylketonuria* - **Phenylketonuria (PKU)** is a metabolic disorder involving the inability to metabolize **phenylalanine**, leading to its accumulation in the blood. - Diagnosis is typically made via **newborn screening** using blood tests, not sweat chloride levels. *Gaucher's disease* - **Gaucher's disease** is a lysosomal storage disorder caused by a deficiency in the enzyme **beta-glucosidase**, leading to lipid accumulation. - Diagnosis involves enzyme assays from blood or tissue samples, or genetic testing, not sweat chloride analysis. *Osteogenesis imperfecta* - **Osteogenesis imperfecta** is a genetic disorder of **collagen synthesis**, primarily characterized by bone fragility, blue sclerae, and hearing loss. - Diagnosis is based on clinical features, imaging, and genetic testing, with no relevance to sweat chloride levels. *Tay-Sachs disease* - **Tay-Sachs disease** is a lysosomal storage disorder caused by deficiency of **hexosaminidase A**, leading to accumulation of GM2 ganglioside in neurons. - Diagnosis is made through **enzyme assay** or **genetic testing**, not sweat chloride measurement.

Question 71: Which of the following statements about Fragile X syndrome is true?

A. Triple nucleotide CAG Sequence mutation
B. Males have IQ 20-40 (Correct Answer)
C. Gain of function mutation
D. 25-30% Female carriers have intellectual disability
E. Autosomal dominant inheritance pattern

Explanation: ***Males have IQ 20-40*** - Males with Fragile X syndrome typically exhibit **moderate to severe intellectual disability**, with IQ scores commonly ranging from 20 to 40. - This intellectual impairment is a hallmark feature due to the **loss of FMRP protein function** in brain development. *Triple nucleotide CAG Sequence mutation* - Fragile X syndrome is caused by an expansion of a **CGG triplet repeat** (not CAG) in the **FMR1 gene**. - This CGG repeat expansion leads to **hypermethylation** and silencing of the FMR1 gene. *25-30% Female carriers have intellectual disability* - While some female carriers may experience milder symptoms or learning disabilities, only about **50% of female carriers have intellectual disability**, typically mild, not 25-30%. - The variable expressivity in females is due to **X-inactivation**, where the unaffected X chromosome can partially compensate. *Gain of function mutation* - Fragile X syndrome is caused by a **loss of function mutation** in the **FMR1 gene** due to the CGG repeat expansion. - This leads to the absence or severe reduction of the **fragile X mental retardation protein (FMRP)**, which is crucial for synaptic development and function. *Autosomal dominant inheritance pattern* - Fragile X syndrome follows an **X-linked dominant inheritance pattern** (not autosomal dominant). - Males are more severely affected than females because they have only one X chromosome, while females have two X chromosomes (one may be unaffected).

Question 72: Risk of genetic diseases in consanguineous marriage between first cousins?

A. 1-2%
B. 4-8% (Correct Answer)
C. 8-10%
D. 12-14%
E. 2-4%

Explanation: ***4-8%*** - The risk of genetic diseases in offspring from a **first-cousin consanguineous marriage** is generally estimated to be **two- to threefold higher than the baseline risk** in the general population. - While the general population risk for a serious birth defect or genetic disease is around 3-4%, this increased risk typically places the range for first cousins at **4-8%**. *1-2%* - This percentage represents a **lower risk than what is typically observed** with first-cousin consanguinity. - The baseline risk for genetic disease in the general population is usually around 3-4%, and consanguineous unions significantly increase this risk. *2-4%* - This represents approximately the **baseline population risk** without consanguinity, not the increased risk seen with first-cousin marriages. - Students may incorrectly assume that first-cousin marriage does not significantly elevate the baseline genetic disease risk. *8-10%* - While there is an increased risk, this range is generally considered **higher than the average estimated risk** for first-cousin consanguineous marriages, which is typically quoted at 4-8%. - This higher range might be seen in cases of **more distant consanguinity** or in populations with a **higher prevalence of specific recessive conditions**. *12-14%* - This magnitude of risk is usually associated with **closer degrees of consanguinity**, such as uncle-niece or half-sibling relationships, rather than first cousins. - The **coefficient of inbreeding** for first cousins is 1/16, which carries a lower risk than these closer relationships.

Question 73: Which of the following statements is MOST accurate regarding ataxia telangiectasia?

A. Autosomal recessive inheritance
B. Increased risk of certain malignancies (Correct Answer)
C. Increased levels of alpha-fetoprotein (AFP) in serum
D. Progressive cerebellar ataxia
E. Oculocutaneous telangiectasias

Explanation: ***Increase in AFP*** - Ataxia telangiectasia is associated with elevated **alpha-fetoprotein (AFP)** levels due to impaired liver function and cellular responses. - This condition is linked with immunodeficiency, leading to abnormal AFP metabolism in affected individuals. *Autosomal dominant* - Ataxia telangiectasia follows an **autosomal recessive** inheritance pattern, not dominant [1]. - It is caused by mutations in the **ATM gene**, which is involved in DNA repair. *Increases the risk of squamous cell carcinoma* - While ataxia telangiectasia patients have a higher risk of **lymphoma** and **leukemia**, they do not have a significant increased risk for **squamous cell carcinoma**. - The malignancy risk is more associated with **lymphoid tissues**, rather than skin cancers. *None of above* - This option is incorrect as the **increased AFP** in ataxia telangiectasia is a well-documented clinical feature. - Hence, stating that "none of the above" is true is inaccurate. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1300-1301.

Question 74: What is the current medical terminology used to refer to Down syndrome?

A. Trisomy 21 (Correct Answer)
B. Chromosomal disorder
C. Genetic disorder
D. Trisomy 18
E. Trisomy 13

Explanation: ***Trisomy 21*** - This is the **correct and most specific medical terminology** for Down syndrome, indicating the presence of an extra copy of chromosome 21. - It directly describes the **genomic abnormality** that causes the syndrome. *Trisomy 18* - This refers to **Edwards syndrome**, a different chromosomal disorder caused by an extra copy of chromosome 18. - While also a trisomy, it is clinically distinct from Down syndrome with different characteristic features. *Trisomy 13* - This refers to **Patau syndrome**, another chromosomal disorder caused by an extra copy of chromosome 13. - Like Trisomy 18, it is a distinct trisomy condition but not the correct terminology for Down syndrome. *Chromosomal disorder* - This is a **broad category** that includes Down syndrome but is not the specific medical term. - Many conditions, like Turner syndrome or Klinefelter syndrome, are also chromosomal disorders, but they are genetically and clinically distinct. *Genetic disorder* - This is an **even broader category** encompassing any disease caused by a genetic abnormality. - While Down syndrome is indeed a genetic disorder, this term is not specific enough to identify it.

Question 75: Which of the following is a characteristic feature of DiGeorge syndrome?

A. Hypoparathyroidism leading to tetany (Correct Answer)
B. Eczema
C. Normal B-cell function with T-cell deficiency
D. Partial T-cell deficiency
E. Hyperparathyroidism with hypercalcemia

Explanation: ***Hypoparathyroidism leading to tetany*** - DiGeorge syndrome is characterized by **thymic and parathyroid hypoplasia or aplasia**, due to a deletion on **chromosome 22q11.2**. - **Hypoparathyroidism** results in **hypocalcemia**, which can manifest as **tetany** (muscle spasms due to low calcium). - This is a classic and highly characteristic feature of DiGeorge syndrome. *Eczema* - While patients with immune deficiencies, including some with DiGeorge syndrome, can be prone to skin infections, **eczema** is not a primary or characteristic feature used for diagnosis. - Eczema is more commonly associated with other immune disorders like **Wiskott-Aldrich syndrome** or severe combined immunodeficiency, but not typically DiGeorge syndrome. *Normal B-cell function with T-cell deficiency* - DiGeorge syndrome is characterized by **T-cell deficiency** due to thymic abnormalities; however, B-cell function can be affected indirectly or through other mechanisms, making "normal B-cell function" not universally accurate. - While **T-cell deficiency** is a hallmark, the precise nature of B-cell involvement can vary, and often B-cell function is also impaired, albeit less directly. *Partial T-cell deficiency* - Although it's often described as a **partial T-cell deficiency**, a more precise characteristic is the **thymic hypoplasia or aplasia**, which directly impairs T-cell development. - The degree of T-cell deficiency can vary from mild to severe, but identifying the underlying cause of **hypoparathyroidism** is a more specific diagnostic feature. *Hyperparathyroidism with hypercalcemia* - This is the **opposite** of what occurs in DiGeorge syndrome. - DiGeorge syndrome presents with **hypoparathyroidism and hypocalcemia**, not hyperparathyroidism. - Hyperparathyroidism would cause elevated calcium levels, which is not seen in this condition.

Question 76: Alagille syndrome - which of the following statements is false?

A. Mutation in JAG 1 And Notch2 gene are seen
B. Autosomal Recessive Disease (Correct Answer)
C. Does not cause Autoimmune hepatitis
D. Valvular anomalies of heart are seen
E. Posterior embryotoxon is a characteristic ocular finding

Explanation: ***Autosomal Recessive Disease*** - Alagille syndrome is an **autosomal dominant** disorder, meaning only one copy of the mutated gene is needed to cause the condition. - The mode of inheritance is critical for genetic counseling and understanding disease patterns within families. *Mutation in JAG 1 And Notch2 gene are seen* - Alagille syndrome is primarily caused by mutations in the **JAG1 gene** (94% of cases), which encodes a ligand for the Notch receptor. - While less common, mutations in the **NOTCH2 gene** can also lead to Alagille syndrome, as both genes are part of the Notch signaling pathway essential for development. *Does not cause Autoimmune hepatitis* - Alagille syndrome is a multisystem disorder characterized by **cholestasis** due to bile duct paucity, which is distinct from autoimmune hepatitis. - Although both involve liver pathology, autoimmune hepatitis is an inflammatory process mediated by the immune system, and it is not a direct feature or cause of Alagille syndrome. *Valvular anomalies of heart are seen* - **Pulmonary artery stenosis** (peripheral or main) is the most common cardiac anomaly found in Alagille syndrome, occurring in over 90% of affected individuals. - Other cardiac defects, such as **tetralogy of Fallot**, are also observed, highlighting the syndrome's impact on cardiovascular development. *Posterior embryotoxon is a characteristic ocular finding* - **Posterior embryotoxon** (a prominent, anteriorly displaced Schwalbe line) is present in approximately **90% of patients** with Alagille syndrome. - This ocular finding is one of the five major diagnostic criteria for the syndrome, along with cholestasis, cardiac defects, skeletal abnormalities, and characteristic facial features.

Question 77: Which of the following is NOT a feature of CHARGE syndrome?

A. Esophageal Atresia (Correct Answer)
B. Congenital heart disease
C. Urinary tract defects
D. Eye Coloboma
E. Choanal Atresia

Explanation: ***Esophageal Atresia*** - While other **tracheoesophageal abnormalities** can occur in CHARGE syndrome, **esophageal atresia** is not typically considered one of the core diagnostic criteria. - The acronym CHARGE stands for a specific set of features, and esophageal atresia is not directly included, unlike **choanal atresia**. *Eye Coloboma* - **Coloboma** of the eye, particularly the iris or retina, is a **major diagnostic feature** of CHARGE syndrome. - This congenital malformation results from incomplete closure of the **choroid fissure** during development. *Congenital heart disease* - Various types of **congenital heart defects**, such as **tetralogy of Fallot** or an **atresia of the aortic valve**, are common in CHARGE syndrome. - These cardiac anomalies are a **major diagnostic criterion** and significantly impact patient management. *Choanal Atresia* - **Choanal atresia** represents the "A" in the CHARGE acronym and is a **major diagnostic criterion**. - This condition involves blockage of the nasal passages and is one of the most characteristic features of the syndrome. *Urinary tract defects* - **Genital and urinary abnormalities** are frequently observed in individuals with CHARGE syndrome. - These can include **hypoplastic genitalia** and **kidney abnormalities**, classifying as a **minor diagnostic feature**.

Question 78: All of the following are true about Down syndrome except for one.

A. Incidence of Robertsonian translocation is 1:1000 (Correct Answer)
B. Most common cause is trisomy 21
C. Mosaicism 21 has no association with maternal age
D. Extra chromosome is of maternal origin
E. Incidence increases with advanced maternal age

Explanation: **Incidence of Robertsonian translocation is 1:1000** - This statement is **not accurate** for Down syndrome. Robertsonian translocation accounts for only about **3-4% of Down syndrome cases**, not a general population incidence of 1:1000. - The vast majority of Down syndrome cases (~95%) are due to trisomy 21 from nondisjunction, not translocation. - This is the **correct answer** as it is the FALSE statement. *Extra chromosome is of maternal origin* - In approximately **90-95% of Down syndrome cases**, the extra copy of chromosome 21 originates from the mother due to **nondisjunction** during meiosis. - This maternal origin is strongly correlated with **advanced maternal age**. *Most common cause is trisomy 21* - **Trisomy 21** (due to meiotic nondisjunction) accounts for about **95% of all Down syndrome cases**, making it the most common genetic mechanism. - This results in three separate copies of chromosome 21 in all body cells. *Mosaicism 21 has no association with maternal age* - **Mosaic Down syndrome** occurs when nondisjunction happens *after fertilization* in early embryonic development, leading to a mixture of cells with normal and trisomic cells. - Because it is a **post-zygotic event**, its incidence is independent of **maternal age**, unlike full trisomy 21. *Incidence increases with advanced maternal age* - **TRUE statement** - The risk of Down syndrome (particularly trisomy 21) increases significantly with **maternal age**. - Risk is approximately 1:1500 at age 20, 1:1000 at age 30, 1:400 at age 35, and 1:100 at age 40. - This is due to increased risk of meiotic nondisjunction in older oocytes.

Question 79: Which of the following is not a typical symptom of Duchenne Muscular Dystrophy (DMD)?

A. Muscle pseudo hypertrophy
B. Muscle weakness
C. Tenderness in muscles (Correct Answer)
D. Cardiomyopathy
E. Gower's sign

Explanation: ***Tenderness in muscles*** - **Muscle tenderness** and pain are **not typical primary symptoms** of Duchenne Muscular Dystrophy (DMD); the disease is characterized by progressive muscle weakness without significant pain. - While some discomfort might arise from muscle spasms or joint issues, widespread tenderness is characteristic of inflammatory conditions, not DMD. *Muscle pseudo hypertrophy* - **Pseudohypertrophy**, particularly in the calves, is a **hallmark sign** of DMD, caused by the replacement of muscle tissue with fat and connective tissue, making the muscles appear larger but weaker. - This symptom reflects the underlying muscle degeneration in DMD. *Muscle weakness* - **Progressive muscle weakness** is the defining characteristic of DMD, typically starting in the proximal muscles and leading to significant functional impairment. - This weakness is due to the lack of **dystrophin**, which is crucial for muscle fiber integrity. *Cardiomyopathy* - **Cardiomyopathy** is a **common and serious complication** of DMD, affecting nearly all patients by adolescence or early adulthood due to the absence of dystrophin in cardiac muscle. - It often manifests as **dilated cardiomyopathy**, contributing significantly to morbidity and mortality. *Gower's sign* - **Gower's sign** is a **classic clinical manifestation** of DMD, where the child uses their hands to "walk up" their legs when rising from the floor due to proximal muscle weakness. - This sign typically appears early in the disease course and is a key diagnostic indicator.

Question 80: Which of the following is not typically associated with Treacher Collins syndrome?

A. Conductive deafness
B. Cleft palate
C. Mandibular hypoplasia
D. Choanal atresia (Correct Answer)
E. Malar hypoplasia

Explanation: Choanal atresia - While Treacher Collins syndrome involves various craniofacial anomalies, **choanal atresia** (blockage of the nasal airway) is **not a typical** or defining feature. - Choanal atresia is more commonly associated with conditions like **CHARGE syndrome** or isolated congenital defects. *Conductive deafness* - **Conductive deafness** is a common feature of Treacher Collins syndrome due to malformations of the **ossicles** and external ear structures. - The abnormal development of middle ear components prevents proper sound transmission, occurring in approximately **50% of cases**. *Cleft palate* - Although less frequent than other features, a **cleft palate** can occur in some individuals with Treacher Collins syndrome, especially in more severe cases. - It results from incomplete fusion of the palatal shelves during embryonic development, occurring in approximately **28-35% of cases**. *Mandibular hypoplasia* - **Mandibular hypoplasia** (underdevelopment of the jaw) is a **hallmark characteristic** of Treacher Collins syndrome, leading to a small chin and retrognathia. - This often contributes to feeding and breathing difficulties in affected individuals. *Malar hypoplasia* - **Malar hypoplasia** (underdevelopment of the cheekbones) is a **classic and defining feature** of Treacher Collins syndrome. - This results in flattened cheeks and contributes to the characteristic facial appearance of the condition.

Question 81: In which condition is the presence of an extra pair of ribs sometimes observed?

A. Down syndrome
B. Turner syndrome (Correct Answer)
C. Holt-Oram syndrome
D. Fibrous dysplasia
E. Klinefelter syndrome

Explanation: ***Turner syndrome*** - **Turner syndrome** (45,X) is often associated with skeletal abnormalities, including an extra pair of ribs (cervical ribs) in some cases. - Other common skeletal features include **short stature**, a **shield chest**, and **cubitus valgus**. *Down syndrome* - **Down syndrome** (trisomy 21) is characterized by specific facial features, intellectual disability, and congenital heart defects. - While it can manifest with various skeletal anomalies, an extra pair of ribs is not a characteristic feature. *Klinefelter syndrome* - **Klinefelter syndrome** (47,XXY) is characterized by hypogonadism, tall stature, gynecomastia, and learning difficulties. - Skeletal features may include long limbs and decreased bone density, but cervical ribs are not typically associated with this condition. *Holt-Oram syndrome* - **Holt-Oram syndrome** is a genetic disorder affecting heart and limb development, specifically the upper limbs (thumb abnormalities, phocomelia). - It does not typically involve the presence of an extra pair of ribs. *Fibrous dysplasia* - **Fibrous dysplasia** is a bone disorder where normal bone is replaced by fibrous tissue, leading to weakened bone and fractures. - It is a localized bone condition and does not involve the presence of supernumerary ribs.

Question 82: What is the name of the syndrome associated with the deletion of chromosome 22?

A. Down syndrome
B. Di George syndrome (Correct Answer)
C. Turner syndrome
D. Klinefelter syndrome
E. Prader-Willi syndrome

Explanation: ***Di George syndrome*** - Di George syndrome, also known as **22q11.2 deletion syndrome**, is caused by a deletion on the long arm of chromosome 22. - This syndrome is associated with varied clinical features, including **congenital heart defects**, **thymic hypoplasia** (leading to immune deficiencies), **hypocalcemia** due to parathyroid hypoplasia, and characteristic facial features. *Down syndrome* - Down syndrome is caused by a **trisomy of chromosome 21**, meaning there's an extra copy of chromosome 21. - It is characterized by intellectual disability, distinctive facial features, and developmental delays, and is not associated with chromosome 22 deletion. *Turner syndrome* - Turner syndrome is a chromosomal condition affecting females, characterized by the partial or complete absence of one of the **X chromosomes (45, X0)**. - It leads to short stature, ovarian dysfunction, and characteristic physical features, unrelated to chromosome 22. *Klinefelter syndrome* - Klinefelter syndrome is a chromosomal disorder in males resulting from an extra **X chromosome (47, XXY)**. - Individuals often experience hypogonadism, reduced fertility, and abnormal body proportions, which is distinct from a deletion on chromosome 22. *Prader-Willi syndrome* - Prader-Willi syndrome is caused by a **deletion of paternal chromosome 15q11-q13** or maternal uniparental disomy. - It presents with hypotonia, hyperphagia, obesity, intellectual disability, and hypogonadism, unrelated to chromosome 22 deletion.

Question 83: What is the chance of a child being a carrier of cystic fibrosis if both parents are carriers?

A. 50% (Correct Answer)
B. 80%
C. 25%
D. 70%
E. 75%

Explanation: ***50%*** - When both parents are **carriers** for an **autosomal recessive** condition like cystic fibrosis, they each carry one normal allele (F) and one mutated allele (f). - A Punnett square (Ff x Ff) shows the offspring genotypes will be 25% FF (unaffected, non-carrier), **50% Ff (unaffected carrier)**, and 25% ff (affected with cystic fibrosis). *25%* - This percentage represents the chance of a child inheriting **two copies of the mutated allele (ff)** and thus being affected with cystic fibrosis. - It does not represent the chance of being an unaffected carrier. *75%* - This represents the probability of a child being **unaffected** (either non-carrier or carrier combined: 25% FF + 50% Ff). - It does not specifically represent the carrier probability alone, which is 50%. *70%* - This percentage is not consistent with the genetic probabilities of an autosomal recessive inheritance pattern. - It does not reflect a standard outcome for carrier probabilities in this scenario. *80%* - This percentage is not consistent with the genetic probabilities of an autosomal recessive inheritance pattern. - It does not reflect a standard outcome for carrier probabilities in this scenario.

Question 84: Which of the following is not a characteristic of Fragile X syndrome?

A. Large nose (Correct Answer)
B. Large ear
C. Large testis
D. Large head
E. Long narrow face

Explanation: **Large nose** - **Large nose** is generally not considered a characteristic feature of **Fragile X syndrome**. - While individuals with Fragile X syndrome have distinct facial features, a prominent or large nose is not typically among them. *Large head* - **Macrocephaly** (large head circumference) is a recognized physical feature in many individuals with **Fragile X syndrome**. - This characteristic often becomes more apparent in infancy and childhood. *Large ear* - **Large, prominent ears** are a very common and classic physical characteristic observed in individuals with **Fragile X syndrome**. - This feature is often noted during developmental assessments. *Large testis* - **Macro-orchidism** (enlarged testes) is a hallmark physical characteristic of **Fragile X syndrome** in post-pubertal males. - This is a highly specific finding and a key diagnostic pointer for the syndrome in adolescent and adult males. *Long narrow face* - **Long, narrow face** with a prominent forehead and jaw is a typical facial feature of **Fragile X syndrome**. - This characteristic facial appearance is part of the recognizable phenotype of the syndrome.

Question 85: Which is the most common genetic cause of mental retardation?

A. Tuberous sclerosis
B. Cri-du-chat syndrome
C. Fragile X syndrome (Correct Answer)
D. Angelman syndrome
E. Down syndrome

Explanation: ***Fragile X syndrome*** - This is the most common **inherited cause** of **intellectual disability** and the second most common overall genetic cause after **Down syndrome**. - It is caused by an expansion of the **CGG trinucleotide repeat** in the **FMR1 gene** on the X chromosome, leading to reduced or absent **Fragile X Mental Retardation Protein (FMRP)**. - In the context of **inherited** genetic causes (following Mendelian inheritance patterns), Fragile X is the most prevalent. *Down syndrome* - This is the most common **overall genetic cause** of intellectual disability, occurring in approximately **1 in 700 live births**. - It is caused by **trisomy 21** (an extra copy of chromosome 21), typically due to nondisjunction during meiosis. - While it is a genetic cause, it is usually a **de novo chromosomal abnormality** rather than an inherited condition, which distinguishes it from Fragile X syndrome. *Tuberous sclerosis* - This is a neurocutaneous disorder characterized by **non-malignant tumors** in multiple organs, including the brain, skin, and kidneys. - While it can cause intellectual disability, it is not the most common genetic cause; its prevalence is lower than Fragile X syndrome. *Cri-du-chat syndrome* - This syndrome is caused by a **deletion** on the **short arm of chromosome 5** and is characterized by a distinctive **cat-like cry** in infancy, intellectual disability, and microcephaly. - While it causes intellectual disability, it is rarer than Fragile X syndrome. *Angelman syndrome* - This syndrome is a neurodevelopmental disorder typically caused by a **deletion or mutation** on the maternal copy of **chromosome 15q11-q13**, or **paternal uniparental disomy**. - It presents with severe developmental delay, **ataxia**, **seizures**, and a happy demeanor, but it is less common than Fragile X syndrome as a genetic cause of mental retardation.

Question 86: Which of the following is NOT a characteristic of LEOPARD syndrome?

A. Growth retardation
B. ECG changes
C. Hypertelorism
D. Hypergonadism (Correct Answer)
E. Lentigines

Explanation: ***Hypergonadism*** - **LEOPARD syndrome** is characterized by **hypogonadism** (underdevelopment or dysfunction of the gonads) and delayed puberty, not hypergonadism. - The acronym LEOPARD stands for multiple clinical features which include **L**entigines, **E**CG conduction abnormalities, **O**cular hypertelorism, **P**ulmonary stenosis, **A**bnormal genitalia, **R**etardation of growth, and **D**eafness. *Growth retardation* - **Retardation of growth** is a defining characteristic of LEOPARD syndrome, often manifesting as short stature. - This is part of the "R" in the LEOPARD acronym, indicating a failure to achieve normal growth milestones. *ECG changes* - **ECG conduction abnormalities** (such as prolonged PR interval, bundle branch block, or Wolff-Parkinson-White syndrome) are primary diagnostic features. - These cardiac issues can be significant and contribute to the morbidity associated with the syndrome. *Hypertelorism* - **Ocular hypertelorism**, meaning widely spaced eyes, is a common facial dysmorphism found in individuals with LEOPARD syndrome. - This feature is represented by the "O" in the LEOPARD acronym, along with other craniofacial anomalies. *Lentigines* - **Lentigines** are multiple pigmented macules (small, flat, darkened spots) that are the hallmark dermatologic feature of LEOPARD syndrome. - These represent the "L" in the LEOPARD acronym and are typically present from early childhood, increasing in number with age.

Question 87: Which of the following features is NOT typically associated with Fragile X syndrome?

A. Enlarged testes
B. Prominent facial features
C. Small ears (Correct Answer)
D. Intellectual disability
E. Microcephaly

Explanation: ***Small ears*** - **Small ears** are not a typical feature of Fragile X syndrome; individuals often have **large, prominent ears**. - This question asks for the feature *not* typically associated with the syndrome. *Intellectual disability* - **Intellectual disability**, particularly in males, is the most common and defining feature of Fragile X syndrome. - It usually ranges from **mild to severe**, affecting cognitive function and adaptive skills. *Enlarged testes* - **Macroorchidism** (enlarged testes) is a characteristic physical finding in postpubertal males with Fragile X syndrome. - This symptom becomes apparent after puberty and is an important diagnostic clue. *Prominent facial features* - **Prominent facial features** are typical, including a **long face**, **prominent jaw (prognathism)**, and **large, prominent ears**. - These features become more noticeable with age. *Microcephaly* - **Microcephaly** (abnormally small head) is not typically associated with Fragile X syndrome. - Individuals with Fragile X generally have **normal or slightly increased head circumference**, not microcephaly.

Question 88: A child with microcephaly, blue eyes, fair skin, and intellectual disability is likely to have:

A. Phenylketonuria (PKU) (Correct Answer)
B. Homocystinuria
C. Tyrosinosis
D. Alkaptonuria
E. Maple syrup urine disease

Explanation: ***Phenylketonuria (PKU)*** - PKU is an **autosomal recessive** metabolic disorder where the body cannot break down **phenylalanine** due to a deficiency in the enzyme **phenylalanine hydroxylase**. - Accumulation of phenylalanine causes **neurotoxicity**, leading to **microcephaly**, **intellectual disability**, seizures, and a characteristic **fair skin** and **blue eyes** due to reduced melanin production. *Homocystinuria* - This is an **autosomal recessive** disorder of methionine metabolism, leading to the accumulation of **homocysteine** in the blood and urine. - Clinical features include **ectopia lentis** (dislocated ocular lenses), skeletal abnormalities, **thromboembolism**, and developmental delay, but typically not microcephaly with fair skin and blue eyes as primary features. *Tyrosinosis* - Refers to a group of disorders (Types I, II, and III) involving the metabolism of **tyrosine**. - Manifestations vary but can include **liver disease** (Type I), **ocular and skin lesions** (Type II), and **neurological symptoms** (Type III), but the specific constellation of microcephaly, fair skin, and blue eyes is not characteristic. *Alkaptonuria* - This is an **autosomal recessive** disorder caused by a deficiency of the enzyme **homogentisate 1,2-dioxygenase**, leading to the accumulation of homogentisic acid. - Key features include **dark urine** (blackens on standing), **ochronosis** (dark pigmentation of cartilage and connective tissue, especially in the ears and sclera), and **osteoarthritis**, but not microcephaly or the described pigmentary changes. *Maple syrup urine disease* - This is an **autosomal recessive** disorder of branched-chain amino acid metabolism (leucine, isoleucine, valine) due to deficiency of **branched-chain alpha-keto acid dehydrogenase**. - Clinical features include **sweet maple syrup odor** of urine and cerumen, **encephalopathy**, feeding difficulties, and developmental delay, but not the characteristic fair skin and blue eyes seen in PKU.

Question 89: Cystic hygroma is associated with which of the following syndromes?

A. Turner syndrome (Correct Answer)
B. Klinefelter syndrome
C. Marfan syndrome
D. Down syndrome
E. Patau syndrome

Explanation: ***Turner syndrome*** - **Cystic hygroma** is a common Fetal anomaly associated with **Turner syndrome (45,X)**, which is characterized by a single X chromosome. - The cystic hygroma in Turner syndrome is thought to arise from abnormal development of the **lymphatic system**, leading to large lymphatic cysts, particularly in the neck. *Klinefelter syndrome* - **Klinefelter syndrome (47,XXY)** is characterized by an extra X chromosome in males and is typically associated with **testicular atrophy**, **gynecomastia**, and tall stature. - It is **not commonly associated** with cystic hygroma. *Marfan syndrome* - **Marfan syndrome** is an autosomal dominant disorder affecting **connective tissue**, primarily impacting the skeletal, ocular, and cardiovascular systems. - It is characterized by **tall stature**, **arachnodactyly**, **lens dislocation**, and **aortic root dilation**, but not cystic hygroma. *Down syndrome* - **Down syndrome (Trisomy 21)** is characterized by an extra copy of chromosome 21 and is associated with distinct facial features, **intellectual disability**, and various congenital anomalies. - While other anomalies like **duodenal atresia** and **congenital heart defects** (e.g., AVSD) are common, **cystic hygroma is not a primary association** of Down syndrome; it is more characteristic of Turner syndrome. *Patau syndrome* - **Patau syndrome (Trisomy 13)** is characterized by an extra copy of chromosome 13 and is associated with severe intellectual disability, **cleft lip/palate**, **polydactyly**, **holoprosencephaly**, and congenital heart defects. - Cystic hygroma is **not a typical feature** of Patau syndrome.

Question 90: Which of the following is a feature of Patau syndrome (Trisomy 13)?

A. Holoprosencephaly
B. Polydactyly (Correct Answer)
C. Cleft lip
D. Rocker bottom foot
E. Clenched fists with overlapping fingers

Explanation: ***Polydactyly*** - **Polydactyly** (extra fingers or toes) is a classic and highly characteristic feature of **Patau syndrome (Trisomy 13)**, occurring in approximately 75% of cases. - Among the options listed, polydactyly is the most consistently present and recognizable physical marker that distinguishes Patau syndrome in clinical practice. - It represents a peripheral limb malformation that is readily identifiable at birth. *Holoprosencephaly* - **Holoprosencephaly** is indeed a severe and common brain malformation in Patau syndrome (occurring in ~70% of cases). - However, it is a central nervous system defect requiring neuroimaging for diagnosis, not an externally visible physical examination finding. - While highly significant clinically, it is not as immediately apparent as polydactyly during initial physical examination. *Cleft lip* - **Cleft lip and palate** occur frequently in Patau syndrome (60-80% of cases) and are important features. - However, cleft lip is also common in many other conditions (isolated defects, other syndromes) and is less specific to Patau syndrome than polydactyly. - It does not distinguish Patau syndrome as reliably as polydactyly does. *Rocker bottom foot* - **Rocker bottom foot** (prominent heel with rounded sole) is a characteristic deformity more strongly associated with **Edwards syndrome (Trisomy 18)**, not Patau syndrome. - While foot abnormalities can occur in Patau syndrome, the classic rocker bottom foot is a marker for Trisomy 18. *Clenched fists with overlapping fingers* - **Clenched fists with overlapping fingers** (typically with index finger overlapping the third finger and fifth finger overlapping the fourth) is a classic finding in **Edwards syndrome (Trisomy 18)**. - This is not a characteristic feature of Patau syndrome (Trisomy 13).

Question 91: A 10-year-old female patient diagnosed with Down's syndrome, having a mosaicism variety. Often, the IQ of such patients lies in the range of:

A. IQ 50-70 (Correct Answer)
B. IQ 140-170
C. IQ 120-139
D. IQ 25-50
E. IQ 70-85

Explanation: ***IQ 50-70*** - Patients with **mosaic Down syndrome** have a **milder phenotype** compared to those with standard trisomy 21 because only a proportion of their cells carry the extra chromosome 21. - The IQ typically falls in the **50-70 range**, which corresponds to **mild intellectual disability**, making this the most common range for mosaic Down syndrome. - This is **higher than standard trisomy 21** (which typically shows IQ 25-50), reflecting the less severe cognitive impairment in the mosaic form. *IQ 25-50* - This range represents **moderate intellectual disability** and is the typical IQ range for **standard trisomy 21 Down syndrome** (non-mosaic). - While some individuals with mosaic Down syndrome may fall into this range, it is **not the most common** presentation for the mosaic variety, which generally shows milder impairment. *IQ 70-85* - This range represents **borderline intellectual functioning** rather than intellectual disability. - While mosaic Down syndrome has milder symptoms than full trisomy 21, most individuals still demonstrate mild intellectual disability (IQ 50-70) rather than borderline functioning. *IQ 140-170* - This IQ range indicates **very superior intelligence** or **gifted** level, which is not seen in individuals with Down syndrome, regardless of whether it is mosaic or standard trisomy 21. - All forms of Down syndrome involve some degree of **intellectual disability**. *IQ 120-139* - This range indicates **superior intelligence**, which is inconsistent with any form of Down syndrome. - Even with mosaicism reducing severity, intellectual disability is still present and the IQ does not reach normal or above-average ranges.

Question 92: Second most common cause of chromosomal abnormality causing mental retardation

A. Fragile X syndrome
B. Patau syndrome
C. Edward syndrome (Correct Answer)
D. Down syndrome
E. Klinefelter syndrome

Explanation: ***Edward syndrome*** - Edward syndrome, or **Trisomy 18**, is the second most common autosomal trisomy after Down syndrome, and a significant cause of **mental retardation** and severe developmental abnormalities. - It involves an extra copy of chromosome 18, leading to a high mortality rate, with most affected individuals not surviving beyond the first year of life. *Fragile X syndrome* - This is the most common inherited cause of **intellectual disability** and the second most common genetic cause overall after Down syndrome. - It is caused by a mutation in the **FMR1 gene** on the X chromosome, not a chromosomal abnormality in terms of numerical or large structural changes. *Patau syndrome* - Patau syndrome, or **Trisomy 13**, is a less common but very severe chromosomal abnormality, typically leading to early mortality. - While it causes profound intellectual disability, its incidence is lower than Edward syndrome. *Down syndrome* - Down syndrome, or **Trisomy 21**, is the most common chromosomal abnormality and the leading genetic cause of **intellectual disability**. - It is caused by an extra copy of chromosome 21, resulting in characteristic physical features and developmental delays. *Klinefelter syndrome* - Klinefelter syndrome (47,XXY) is a sex chromosome abnormality affecting males, with an incidence of approximately 1 in 500-1,000 male births. - While it may be associated with mild learning difficulties or cognitive impairment, it is not primarily known for causing significant intellectual disability and is less common as a cause of mental retardation compared to the major autosomal trisomies.

Question 93: A 12-year-old child presents with intellectual disability, a large face, a prominent jaw, large ears, and macroorchidism. Which genetic condition is most likely diagnosed?

A. McCune-Albright syndrome
B. Down syndrome
C. Klinefelter syndrome
D. Fragile X syndrome (Correct Answer)
E. Prader-Willi syndrome

Explanation: ***Fragile X syndrome*** - This syndrome is characterized by **intellectual disability**, a distinctive **large face, prominent jaw, large ears**, and **macroorchidism** (enlarged testes) in males. - It is caused by a **CGG trinucleotide repeat expansion** in the *FMR1* gene on the X chromosome, leading to reduced or absent fragile X mental retardation protein (FMRP). *McCune-Albright syndrome* - This syndrome is characterized by a triad of **fibrous dysplasia of bone**, **café-au-lait spots**, and **precocious puberty**, which are not described in the child's presentation. - It is caused by a **somatic mutation** in the *GNAS* gene, affecting various endocrine functions. *Down syndrome* - Down syndrome is associated with distinct facial features such as **upslanting palpebral fissures**, **epicanthal folds**, and a **flat nasal bridge**, along with intellectual disability, but not the specific features of a large face, prominent jaw, large ears, or macroorchidism. - It is primarily caused by **trisomy 21**, an extra copy of chromosome 21. *Klinefelter syndrome* - Klinefelter syndrome (47, XXY) typically presents in males with **tall stature**, **infertility**, and **hypogonadism** (small testes), rather than macroorchidism. - While intellectual disability can occur, the characteristic facial and testicular features described point away from Klinefelter syndrome. *Prader-Willi syndrome* - This syndrome presents with **intellectual disability**, **hypotonia**, **hyperphagia** leading to obesity, and **hypogonadism** (small testes and underdeveloped genitalia), not macroorchidism. - It is caused by deletion or loss of function of genes on the **paternal chromosome 15q11-q13** region.

Question 94: Webbing of the neck, an increased carrying angle, and a low posterior hairline are characteristics of –

A. Klinefelter syndrome
B. Turner syndrome (Correct Answer)
C. Cri du chat syndrome
D. Noonan syndrome
E. Down syndrome

Explanation: ***Turner syndrome*** - **Webbed neck** (pterygium colli), increased **carrying angle** (cubitus valgus), and a **low posterior hairline** are classic physical features of Turner syndrome, a chromosomal disorder. - These features result from the **partial or complete monosomy of the X chromosome**, specifically 45,XO karyotype. *Klinefelter syndrome* - Characterized by a **47, XXY karyotype** in males, leading to features like **tall stature**, hypogonadism, and gynecomastia. - Does not typically present with a webbed neck, increased carrying angle, or a low posterior hairline. *Cri du chat syndrome* - Caused by a **deletion on the short arm of chromosome 5** (5p-). - Its hallmark features include a **high-pitched cry** resembling a cat's meow, microcephaly, and intellectual disability, not the physical characteristics described. *Noonan syndrome* - An autosomal dominant disorder with overlapping features with Turner syndrome, but it affects both males and females and is associated with **normal chromosomes**. - While it can present with a webbed neck and low posterior hairline, it does not involve the characteristic **monosomy X** seen in Turner syndrome. *Down syndrome* - Caused by **trisomy 21** (three copies of chromosome 21). - Characterized by distinctive features including **flat facial profile**, upslanting palpebral fissures, single palmar crease, and intellectual disability. - Does not typically present with webbed neck, increased carrying angle, or low posterior hairline.

Question 95: Which one of the following is a distinguishing feature of Edwards' syndrome?

A. Holoprosencephaly
B. Rocker bottom feet (Correct Answer)
C. Hypotonia
D. Hypotelorism
E. Simian crease

Explanation: ***Rocker bottom feet*** - **Rocker bottom feet** (pes valgus) are a classic and distinguishing skeletal anomaly in infants with **Edwards' syndrome** (Trisomy 18). - This malformation is characterized by a prominent heel and a convex sole, resembling the base of a rocking chair. *Hypotonia* - **Hypotonia** (decreased muscle tone) is a common feature in many genetic syndromes, including **Down syndrome**, but is less specific to **Edwards' syndrome**. - While infants with Edwards' syndrome may exhibit some hypotonia, it is not a hallmark differentiating feature. *Hypotelorism* - **Hypotelorism** refers to closely set eyes, often associated with conditions like **holoprosencephaly**. - It is not a characteristic feature of **Edwards' syndrome**; facial dysmorphisms in Edwards' syndrome typically include a small mouth and micrognathia. *Holoprosencephaly* - **Holoprosencephaly** is a severe brain malformation where the forebrain fails to divide into two cerebral hemispheres, almost exclusively found in **Patau's syndrome (Trisomy 13)** due to its association with midline defects. - This condition is not typically associated with **Edwards' syndrome**. *Simian crease* - A **simian crease** (single transverse palmar crease) is a characteristic feature of **Down syndrome (Trisomy 21)**, not Edwards' syndrome. - This distinctive palm crease is present in approximately 45% of individuals with Down syndrome but is not associated with Edwards' syndrome.

Question 96: What is the chance of a child having cystic fibrosis if both parents are carriers of the disease?

A. 75%
B. 25% (Correct Answer)
C. 50%
D. 0%
E. 100%

Explanation: ***50%*** - If one parent is affected by cystic fibrosis (CF), they are **homozygous for the CFTR mutation**, while the normal parent is likely **homozygous for the normal allele**. - Each child has a **50% chance** of inheriting the **mutated allele** from the affected parent, resulting in an **autosomal recessive** inheritance pattern [1]. *70%* - This percentage does not reflect the inheritance probabilities associated with **autosomal recessive traits** [1], such as cystic fibrosis. - In heterozygous and normal arrangements, the calculation does not support a **70%** inheritance chance of the disease. *80%* - Similarly, an **80% chance** is inaccurate as cystic fibrosis requires two mutated alleles for the disease to manifest [1]. - The inheritance pattern does not allow for a higher than **50% chance** when one parent is normal. *25%* - A **25% chance** applies if both parents were carriers of the CFTR mutation [1]. However, with only one affected parent, this percentage does not apply. - The maximum **chance of inheritance** from one affected and one normal parent is accurately stated as **50%**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 53-54.

Question 97: What is the current appropriate term for Down syndrome?

A. Down syndrome (Correct Answer)
B. Intellectual disability
C. Cognitive impairment
D. Mental retardation
E. Mongolism

Explanation: ***Down syndrome*** - This is the **most appropriate and current term** for the genetic condition caused by the presence of all or part of an extra 21st chromosome, as it is named after **John Langdon Down**, who first described the condition. - The term is precise, respectful, and widely accepted in the **medical and scientific communities** and among advocacy groups. *Intellectual disability* - This is a **general term** used to describe a broad range of conditions characterized by significant limitations in both intellectual functioning and adaptive behavior. - While individuals with Down syndrome often have intellectual disability, it is not the specific name of the **syndrome itself**. *Cognitive impairment* - This term refers to any **decline or deficit in cognitive function**, such as memory, thinking, and reasoning. - It is a **broader descriptive term** and does not specifically identify the genetic condition of Down syndrome. *Mental retardation* - This term is **outdated and considered offensive**, having been replaced in medical and legal contexts by "intellectual disability." - Using this term is no longer appropriate given the **stigma and negative connotations** associated with it. *Mongolism* - This is a **historical term** that was used in the past to describe Down syndrome, coined by John Langdon Down himself. - The term is now **considered obsolete and offensive** due to its racial connotations and is no longer used in medical or professional contexts.

Question 98: What is the most likely diagnosis in an infant who presents with recurrent fractures and multiple bony deformities?

A. Achondroplasia
B. Rickets
C. Osteogenesis imperfecta (Correct Answer)
D. Ehlers-Danlos syndrome
E. Osteopetrosis

Explanation: ***Osteogenesis imperfecta*** - This genetic disorder is characterized by **fragile bones** due to defects in **type I collagen**, leading to recurrent fractures and bony deformities. - Other classic features include **blue sclera**, **dentinogenesis imperfecta**, and **hearing loss**, all stemming from collagen abnormalities. *Achondroplasia* - This is a common cause of **dwarfism** due to a genetic mutation affecting **cartilage formation**, primarily impacting long bone growth. - While it causes short stature and distinct facial features, **recurrent fractures** are not its primary clinical manifestation. *Ehlers-Danlos syndrome* - This group of genetic disorders affects **connective tissues**, resulting in **joint hypermobility**, **skin hyperextensibility**, and tissue fragility. - While it can lead to complications like joint dislocations and vascular issues, **recurrent bony fractures** are not its hallmark; rather, it's connective tissue fragility that is key. *Rickets* - This condition is caused by a **deficiency of vitamin D, calcium, or phosphate**, leading to impaired bone mineralization and bone softening. - It presents with **bowed legs**, **rachitic rosary**, and bone pain, but typically not **recurrent fractures** from fragile bones in infancy, unless severe and prolonged. *Osteopetrosis* - Also known as **marble bone disease**, this genetic disorder causes **abnormally dense bones** due to defective osteoclast function. - While bones are dense, they are paradoxically **brittle and prone to fractures**, but the classic presentation includes **bone sclerosis on X-ray**, **hepatosplenomegaly**, and **cranial nerve compression**, rather than multiple bony deformities typical of osteogenesis imperfecta.

Question 99: Baby born at 30 weeks to an 18-year-old primigravida weighing 2 kg, who died after 48 hours, with Apgar scores of 5 and 8 at 1 and 5 minutes, respectively. On autopsy, bilateral enlarged kidneys with multiple radially arranged cysts were found. Which of the following findings is expected to be associated with this?

A. Congenital absence of ureter
B. Hepatic cyst and fibrosis (Correct Answer)
C. Congenital brain malformation
D. Congenital anorectal malformation
E. Congenital cardiac malformation

Explanation: ***Hepatic cyst and fibrosis*** - The description of **bilateral enlarged kidneys with multiple radially arranged cysts** in a preterm infant is classic for **Autosomal Recessive Polycystic Kidney Disease (ARPKD)**. - **Hepatic cysts** and **congenital hepatic fibrosis** are highly characteristic extrarenal manifestations of ARPKD due to shared developmental origins of the kidney and liver bile ducts. - This is the most common and clinically significant association with ARPKD. *Congenital absence of ureter* - This condition is known as **renal agenesis** or **ureteral atresia**, which typically presents with absent or severely undeveloped kidneys, not enlarged cystic kidneys. - While it can lead to kidney failure, the anatomical findings described (enlarged, radially cystic kidneys) are inconsistent with a primary ureteral agenesis. *Congenital brain malformation* - While some genetic syndromes with renal involvement can have brain anomalies, **ARPKD** is not primarily associated with typical congenital brain malformations. - The primary systemic complications of ARPKD involve the **liver** and sometimes the **lungs** (due to oligohydramnios-induced pulmonary hypoplasia). *Congenital anorectal malformation* - This malformation is typically associated with various genetic syndromes or other developmental defects, but it is **not a characteristic finding** in ARPKD. - ARPKD's primary pathology is confined to the kidneys and liver. *Congenital cardiac malformation* - While cardiac anomalies are common congenital defects, they are **not specifically associated with ARPKD**. - ARPKD is primarily a disease of the kidneys and liver, with the main extrarenal manifestation being hepatic fibrosis and cysts.

Question 100: Goldenhar's complex includes:

A. Branchial cleft anomaly
B. Cardiac defects (Correct Answer)
C. Cystic hygroma
D. Esophageal atresia
E. Hemifacial microsomia

Explanation: ***Cardiac defects*** - **Goldenhar's complex**, also known as **oculo-auriculo-vertebral (OAV) spectrum**, is a congenital condition characterized by developmental anomalies primarily affecting the **first and second pharyngeal arches**. - While its manifestations can vary, **cardiac defects** are a recognized component, with a prevalence of about **15-30%** in affected individuals. - Common cardiac defects include **ventricular septal defects (VSD)**, **atrial septal defects (ASD)**, **tetralogy of Fallot**, and **coarctation of the aorta**. *Hemifacial microsomia* - **Hemifacial microsomia** is actually the **most common feature** of Goldenhar's complex, affecting the mandible, maxilla, and other facial structures on one side. - However, when listing individual components, hemifacial microsomia is considered the **primary facial manifestation** rather than a separate "inclusion" in the complex—it essentially defines the syndrome. - Other classic features include **ear anomalies** (microtia, preauricular tags), **epibulbar dermoids**, and **vertebral anomalies**. *Cystic hygroma* - A **cystic hygroma** is a type of **lymphatic malformation** that typically presents as soft, compressible masses, most commonly in the neck or axilla. - It is not considered a primary or defining feature of **Goldenhar's complex**, although it can occur in various genetic syndromes. *Branchial cleft anomaly* - **Branchial cleft anomalies** result from incomplete obliteration of the **branchial arches** during embryonic development, leading to cysts, sinuses, or fistulas in the neck. - While Goldenhar's complex involves anomalies of the pharyngeal arches, the term "branchial cleft anomaly" usually refers to a distinct set of malformations, and it is not typically grouped under the primary diagnostic criteria for **Goldenhar's complex**. *Esophageal atresia* - **Esophageal atresia** is a congenital condition where the **esophagus** ends in a blind pouch, preventing food from reaching the stomach. - This malformation is often associated with the **VACTERL association** (Vertebral, Anorectal, Cardiac, Tracheoesophageal, Renal, Limb anomalies) but is not a characteristic component of **Goldenhar's complex**.

Question 101: A child with a small head, minor anomalies of the face including a thin upper lip, growth delay, and developmental disability can have all of the following, except:

A. A teratogenic syndrome
B. A Mendelian syndrome
C. A polygenic syndrome (Correct Answer)
D. A chromosomal syndrome
E. A mitochondrial syndrome

Explanation: ***A polygenic syndrome*** - **Polygenic syndromes** involve multiple genes and environmental factors, typically leading to a range of complex traits rather than a distinct set of **major and minor anomalies** as described. - The specific presentation with a small head, facial dysmorphology, growth delay, and developmental disability is generally indicative of a more singular genetic or environmental insult. *A chromosomal syndrome* - Many **chromosomal syndromes**, such as **Down syndrome** or **cri du chat syndrome**, are characterized by a combination of minor facial anomalies, microcephaly, growth delays, and developmental disabilities. - These conditions result from an abnormal number or structure of chromosomes, leading to a wide range of affected genes and developmental pathways. *A teratogenic syndrome* - **Teratogenic syndromes**, like **Fetal Alcohol Syndrome (FAS)**, are caused by exposure to specific environmental agents during prenatal development. - FAS, for instance, classically presents with **microcephaly**, a **thin upper lip**, short palpebral fissures, growth restriction, and CNS dysfunction leading to developmental disabilities. *A Mendelian syndrome* - **Mendelian syndromes** are caused by mutations in a single gene and can manifest with features such as minor anomalies, microcephaly, growth delays, and developmental disability. - Examples include syndromes like **Fragile X syndrome** or **Noonan syndrome**, which fit the general description of the child's presentation. *A mitochondrial syndrome* - **Mitochondrial disorders** can present with developmental disabilities, growth delays, and dysmorphic features due to impaired cellular energy production. - Examples include **MELAS** and **Leigh syndrome**, which can manifest with neurological impairment and developmental delays in childhood.

Question 102: What is the most common chromosomal syndrome?

A. Fragile X syndrome
B. Trisomy 17
C. Trisomy 21 (Correct Answer)
D. Trisomy 13
E. Trisomy 18

Explanation: ***Trisomy 21*** - **Trisomy 21**, also known as Down syndrome, is the most common chromosomal disorder, occurring in approximately 1 in 700 live births. - It is characterized by the presence of an **extra copy of chromosome 21**, leading to intellectual disability and distinctive physical features. *Fragile X syndrome* - **Fragile X syndrome** is the most common inherited cause of intellectual disability, but it is not a chromosomal aneuploidy. - It is caused by a **mutation in the FMR1 gene** on the X chromosome, leading to an expanded CGG repeat. *Trisomy 17* - **Trisomy 17** is generally considered a **lethal chromosomal abnormality**, with most affected fetuses not surviving to term. - It is not a common condition and is rarely seen in live births, unlike Trisomy 21. *Trisomy 18* - **Trisomy 18**, or Edwards syndrome, is the second most common autosomal trisomy, occurring in approximately 1 in 5,000 live births. - It is associated with severe intellectual disability and multiple congenital anomalies, with most infants dying within the first year of life. - While more common than Trisomy 13, it is still significantly less common than Trisomy 21. *Trisomy 13* - **Trisomy 13**, or Patau syndrome, is a severe chromosomal disorder associated with **multiple congenital malformations** and a very poor prognosis, with most infants dying within the first days or weeks of life. - It is less common than Trisomy 21, occurring in approximately 1 in 16,000 live births.

Question 103: Megalencephaly is commonly seen in which condition?

A. Canavan disease
B. Alexander disease
C. Sotos syndrome (Correct Answer)
D. Autism spectrum disorders
E. Fragile X syndrome

Explanation: ***Sotos syndrome*** - **Sotos syndrome** is a genetic disorder characterized by **overgrowth** in childhood, including **macrocrania** (large head circumference) or megalencephaly. - Other features often include a **distinctive facial appearance**, developmental delays, and a high risk of certain tumors. *Canavan disease* - **Canavan disease** is an inherited neurodegenerative disorder that mainly affects the brain's **white matter**. - While it can cause macrocephaly, its primary features are **severe developmental delay**, hypotonia, and **spongiform degeneration** of the brain, not simply generalized megalencephaly as a defining characteristic in the growth pattern. *Alexander disease* - **Alexander disease** is a rare, fatal neurological disorder characterized by the destruction of **myelin** in the brain. - It involves the accumulation of **Rosenthal fibers** and often presents with macrocephaly, but the underlying mechanisms and clinical presentation are primarily driven by **leukodystrophy** rather than an overgrowth syndrome. *Fragile X syndrome* - **Fragile X syndrome** is the most common inherited cause of **intellectual disability** and autism spectrum disorder. - While some individuals may have **macrocephaly**, megalencephaly is not a consistent or defining feature of the syndrome. - The condition is primarily characterized by **cognitive impairment**, behavioral challenges, and distinctive facial features. *Autism spectrum disorders* - While some individuals with **autism spectrum disorders** may have larger head circumferences or even megalencephaly, it is not a universally present or defining feature of the condition. - **Autism** is primarily characterized by challenges in social interaction, communication, and restricted/repetitive behaviors, and megalencephaly is a less specific association.

Question 104: Which of the following is a characteristic feature of Turner's syndrome?

A. Secondary amenorrhea
B. Cognitive impairment
C. Lymphedema of hands and feet (Correct Answer)
D. Presence of XY genotype
E. Tall stature

Explanation: ***Lymphedema of hands and feet*** - **Lymphedema** of the hands and feet, particularly at birth, is a classic feature of **Turner's syndrome** due to impaired lymphatic development. - This symptom results from a **congenital absence or hypoplasia of lymphatic vessels**. *Secondary amenorrhea* - While most individuals with Turner syndrome experience **primary amenorrhea** (absence of menstruation by age 15) due to gonadal dysgenesis, secondary amenorrhea is not the characteristic presentation. - **Primary ovarian insufficiency** leads to absent or very delayed puberty. *Cognitive impairment* - Individuals with Turner syndrome typically have **normal intelligence** but may experience specific neurocognitive challenges, such as difficulties with visual-spatial processing and nonverbal skills. - **Global cognitive impairment** is not a characteristic feature of the syndrome. *Presence of XY genotype* - Turner syndrome is characterized by the absence of all or part of one X chromosome, typically resulting in a **45, X0 karyotype**. - The presence of an **XY genotype** is characteristic of males and would rule out Turner syndrome. *Tall stature* - **Short stature** is one of the most consistent features of Turner syndrome, present in nearly all affected individuals. - Adult height without growth hormone treatment typically ranges from 143-145 cm (4'8"-4'9"). - Tall stature would be inconsistent with Turner syndrome diagnosis.

Question 105: A child presents with hepatomegaly and bilateral lenticular opacities. Deficiency of which enzyme is least likely to cause these features?

A. Galactose-1-phosphate uridyl transferase
B. UDP-galactose-4-epimerase
C. Galactokinase
D. Lactase (Correct Answer)
E. Phosphoglucomutase

Explanation: ***Lactase*** - **Lactase deficiency** primarily causes **lactose intolerance**, leading to gastrointestinal symptoms like bloating and diarrhea due to undigested lactose. - It does not typically result in the accumulation of galactose metabolites that cause **hepatomegaly** or **lenticular opacities** (cataracts). - This is the **least likely** enzyme deficiency to cause the clinical presentation described. *Galactose-1-phosphate uridyl transferase* - Deficiency of this enzyme causes **Classic Galactosemia (Type I)**, leading to the accumulation of **galactose-1-phosphate**. - This accumulation is highly toxic and causes severe symptoms including **hepatomegaly**, **jaundice**, and **cataracts**. *UDP-galactose-4-epimerase* - Deficiency of this enzyme causes **Galactosemia Type III**, impairing the conversion of UDP-galactose to UDP-glucose, leading to the accumulation of **galactose-1-phosphate**. - This can result in a broad spectrum of symptoms, including **hepatomegaly** and **cataracts**. *Galactokinase* - **Galactokinase deficiency (Galactosemia Type II)** leads to the accumulation of **galactose** in the blood and tissues. - The most prominent clinical feature is **infantile cataracts**, which result from the conversion of galactose to **galactitol** in the lens via aldose reductase. **Hepatomegaly** is less common but can occur. *Phosphoglucomutase* - **Phosphoglucomutase deficiency** causes a congenital disorder of glycosylation (CDG) that can present with **hepatomegaly** and various other systemic manifestations. - While cataracts are not the most prominent feature, the enzyme plays a role in galactose metabolism, and deficiency can lead to metabolic disturbances affecting multiple organ systems.

Question 106: Cherry red spot is seen in all except what?

A. Niemann-Pick disease
B. GM1 Gangliosidosis
C. Tay-Sachs disease
D. Gaucher's disease (Correct Answer)
E. Sialidosis

Explanation: ***Gaucher's disease*** - This condition is characterized by a deficiency of the enzyme **glucocerebrosidase**, leading to the accumulation of **glucocerebrosides** in macrophages. - While it can manifest with **hepatosplenomegaly**, bone abnormalities, and neurological symptoms (in severe forms), it **does not typically present with a cherry-red spot** in the retina. *Niemann-Pick disease* - This **lysosomal storage disorder** is caused by a deficiency of **sphingomyelinase**, leading to the accumulation of **sphingomyelin** in various tissues. - A **cherry-red spot** is a classic ophthalmological finding, especially in Type A, due to sphingomyelin accumulation in retinal ganglion cells. *GM1 Gangliosidosis* - This is a rare, inherited disorder caused by a deficiency in the enzyme **beta-galactosidase**, leading to the accumulation of **GM1 gangliosides**. - A **cherry-red spot** can be observed in the retina, along with progressive neurological deterioration and skeletal abnormalities. *Tay-Sachs disease* - This severe **lysosomal storage disease** results from a deficiency of **hexosaminidase A**, causing the accumulation of **GM2 gangliosides** in neurons. - A **cherry-red spot** in the macula is a hallmark finding, as the surrounding retinal ganglion cells become engorged with gangliosides while the foveola remains clear. *Sialidosis* - This **lysosomal storage disorder** is caused by a deficiency of **neuraminidase (sialidase)**, leading to the accumulation of **sialylated glycopeptides and oligosaccharides**. - A **cherry-red spot** is a characteristic finding, particularly in Type I (cherry-red spot myoclonus syndrome), along with myoclonus, seizures, and progressive visual impairment.

Question 107: All the following are characteristic features of Turner syndrome except:

A. Cubitus valgus
B. Webbing of Neck
C. Umbilical Hernia (Correct Answer)
D. Coarctation of Aorta
E. Short stature

Explanation: ***Umbilical Hernia*** - While various **congenital anomalies** can occur in individuals with Turner syndrome, an **umbilical hernia** is not considered a characteristic or commonly associated feature. - The other options represent classic physical findings frequently observed in Turner syndrome. *Cubitus valgus* - This is a common orthopedic finding in Turner syndrome, characterized by an **increased carrying angle** at the elbow. - It results from the skeletal dysplasias associated with the **45,X karyotype**. *Webbing of Neck* - **Pterygium colli**, or webbing of the neck, is a classic and highly recognizable feature of Turner syndrome. - It is caused by **lymphatic abnormalities** during fetal development. *Coarctation of Aorta* - **Cardiovascular malformations**, particularly **coarctation of the aorta** and **bicuspid aortic valve**, are common and serious complications of Turner syndrome. - These conditions require careful monitoring and intervention due to their potential impact on health. *Short stature* - **Short stature** is one of the most universal features of Turner syndrome, present in over **95% of cases**. - Average adult height without growth hormone treatment is approximately **143-145 cm (4'8"-4'9")**. - Results from haploinsufficiency of the **SHOX gene** on the X chromosome.

Question 108: The Simian crease is commonly seen in Down syndrome. In which other condition is it also commonly observed?

A. Klinefelter syndrome
B. Trisomy 13
C. Down syndrome
D. Trisomy 18 (Correct Answer)
E. Cri du chat syndrome

Explanation: ***Trisomy 18 (Edwards syndrome)*** - A **single palmar crease (Simian crease)** is commonly observed in Edwards syndrome, along with other distinctive hand features including **overlapping fingers** and **clenched fists** - Edwards syndrome presents with multiple congenital anomalies including **rocker-bottom feet**, **cardiac defects**, and severe intellectual disability - Like Down syndrome, it is a chromosomal trisomy disorder with characteristic dermatoglyphic findings *Klinefelter syndrome* - Klinefelter syndrome (47,XXY) is characterized by **hypogonadism**, **tall stature**, **gynecomastia**, and **infertility** - Simian crease is **not** a characteristic feature of this sex chromosome disorder - Physical features are primarily related to hypogonadism rather than dysmorphic hand features *Trisomy 13 (Patau syndrome)* - Patients with Trisomy 13 present with severe midline defects including **holoprosencephaly**, **cleft lip/palate**, and **polydactyly** - Hand abnormalities typically include **polydactyly** and **flexion deformities**, but Simian crease is not a prominent feature - Associated with very poor prognosis with most infants dying within the first year *Cri du chat syndrome* - This 5p deletion syndrome is characterized by a distinctive **cat-like cry** in infancy due to laryngeal abnormalities - Features include **microcephaly**, **intellectual disability**, and distinctive facial features - Simian crease is not a common or characteristic finding in this syndrome *Down syndrome* - Cannot be the answer as the question stem already states Simian crease is common in Down syndrome - The **single palmar crease** occurs in approximately **45% of individuals with Down syndrome (Trisomy 21)** - Other characteristic features include epicanthal folds, upward slanting palpebral fissures, flat nasal bridge, and intellectual disability

Question 109: What is the inheritance pattern of Crouzon syndrome?

A. Autosomal recessive
B. X-linked recessive
C. Mitochondrial
D. Autosomal dominant (Correct Answer)
E. X-linked dominant

Explanation: ***Autosomal dominant*** - Crouzon syndrome is caused by a mutation in the **FGFR2 gene**, which is inherited in an **autosomal dominant pattern**. - This means only one copy of the mutated gene is needed for an individual to be affected, and there is a 50% chance of passing it to offspring. *Autosomal recessive* - Autosomal recessive conditions require **two copies of the mutated gene** (one from each parent) for the disease to manifest. - While some craniosynostosis syndromes are autosomal recessive, Crouzon syndrome is not. *X-linked recessive* - **X-linked recessive disorders** primarily affect males, as they only have one X chromosome. - Crouzon syndrome affects both males and females equally, ruling out X-linked inheritance. *X-linked dominant* - **X-linked dominant disorders** affect both males and females but often show more severe manifestations in males. - Crouzon syndrome does not follow an X-linked pattern and is not associated with the X chromosome. *Mitochondrial* - **Mitochondrial inheritance** involves genes within the mitochondrial DNA, passed exclusively from the mother to all her children. - This pattern of inheritance does not match the observed transmission of Crouzon syndrome.

Question 110: Simian crease is not seen in which of the following?

A. Trisomy 13
B. Noonan syndrome
C. Down
D. Atopic dermatitis (Correct Answer)
E. Trisomy 18

Explanation: ***Atopic dermatitis*** - **Atopic dermatitis** is a chronic inflammatory skin condition characterized by **eczematous lesions** and **itching**, and does not involve congenital hand abnormalities. - A **Simian crease** (single palmar crease) is a feature associated with certain chromosomal disorders, not skin conditions. *Down* - **Down syndrome** (Trisomy 21) is strongly associated with the presence of a **Simian crease**, along with other distinctive facial and physical features. - This chromosomal anomaly affects development and often results in characteristic dermatoglyphic patterns. *Trisomy 13* - **Trisomy 13** (Patau syndrome) is a severe chromosomal disorder that frequently presents with a **Simian crease** as one of its many congenital abnormalities. - Other features include **polydactyly**, **cleft lip/palate**, and severe intellectual disability. *Trisomy 18* - **Trisomy 18** (Edwards syndrome) is another severe chromosomal disorder commonly associated with a **Simian crease**. - Other features include **clenched fists with overlapping fingers**, **rocker-bottom feet**, and severe intellectual disability. *Noonan syndrome* - While not as classically associated as Down or Trisomy 13, **Noonan syndrome** can sometimes include a **Simian crease** among its varied developmental features. - It is a genetic condition characterized by distinctive facial features, **short stature**, and heart defects, rather than a chromosomal anomaly.

Question 111: A one-year-old child, who was previously normal, is suffering from copious nasal discharge, coarse facial features, a large tongue, a bulging head, and a flattened nose. He is also experiencing an enlarged spleen and liver. What is the most likely diagnosis?

A. Hypothyroidism
B. Proteus syndrome
C. Hurler syndrome (Correct Answer)
D. Beckwith-Wiedemann syndrome
E. Hunter syndrome

Explanation: ***Hurler syndrome*** - Characterized by **mucopolysaccharidosis**, leading to features like **coarse facial features**, **enlarged tongue**, and **bulging head** [1]. - The presence of **hepatosplenomegaly** and respiratory symptoms like nasal discharge aligns well with this metabolic disorder [1]. *Proteus syndrome* - Primarily presents with **overgrowth** of tissues and is often associated with **skin lesions**, which are not described in this case. - Does not typically involve **systemic symptoms** like liver and spleen enlargement or respiratory distress as seen here. *Hypothyroidism* - Would lead to **growth retardation** and features like **dry skin** or **goiter**, but not the **coarse facial features** or nasopharyngeal symptoms. - Cannot satisfactorily explain the **hepatosplenomegaly** and characteristic facial features present in this child. *Beckwith widman syndrome* - Mainly marked by **organomegaly**, **macroglossia**, and **abdominal wall defects**, but coarse features is not a significant finding. - The symptoms of **respiratory distress** and facial changes do not correlate with this syndrome's typical presentation. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 163-164.

Question 112: An infant with intolerance to breast milk, vomiting, and diarrhea develops cataracts. Which of the following is the most likely diagnosis?

A. Galactosemia (Correct Answer)
B. Fabry disease
C. Lowe syndrome
D. Congenital hypoglycemia
E. Homocystinuria

Explanation: **Galactosemia** - **Galactosemia** is an inborn error of metabolism where the body is unable to process **galactose**, leading to its build-up. - Symptoms such as **vomiting**, **diarrhea**, **failure to thrive** (intolerance to breast milk containing lactose, which is broken down into glucose and galactose), and **cataracts** are classic signs of galactosemia in infants. *Lowe syndrome* - Also known as **oculocerebrorenal syndrome**, Lowe syndrome is an X-linked disorder characterized by **congenital cataracts**, **renal tubular dysfunction**, and **intellectual disability**. - While cataracts are present, it primarily presents with **kidney and brain abnormalities**, not predominantly with GI symptoms like vomiting and diarrhea upon feeding. *Fabry disease* - **Fabry disease** is an X-linked lysosomal storage disorder caused by a deficiency of the enzyme **alpha-galactosidase A**. - It is characterized by **neuropathic pain**, **angiokeratomas**, **renal disease**, and **cardiac involvement**, and is not typically associated with infantile vomiting, diarrhea, or early onset cataracts from breast milk intolerance. *Homocystinuria* - **Homocystinuria** is an inherited disorder of methionine metabolism due to **cystathionine beta-synthase deficiency**. - It presents with **lens dislocation** (ectopia lentis), **intellectual disability**, **skeletal abnormalities** (marfanoid habitus), and **thromboembolism**, typically becoming apparent in later infancy or childhood, not with acute feeding intolerance and GI symptoms in early infancy. *Congenital hypoglycemia* - **Congenital hypoglycemia** refers to abnormally low blood glucose levels at birth or shortly after. - Symptoms include **poor feeding**, **lethargy**, **irritability**, and **seizures**, but it is not typically associated with cataracts or specific intolerance to breast milk causing vomiting and diarrhea as seen in metabolic disorders.

Question 113: All of the following are seen in RASopathies except which of the following?

A. Sparse curly hair
B. Distinct craniofacial features
C. Keratosis pilaris
D. Desquamation of skin (Correct Answer)
E. Palmoplantar hyperkeratosis

Explanation: ***Desquamation of skin*** - **Desquamation (skin peeling)** is generally not considered a characteristic feature of RASopathies. - While various skin issues can occur, widespread desquamation is more typical of other conditions like **ichthyosis** or severe inflammatory dermatoses. - This is the **correct answer** as it is NOT typically seen in RASopathies. *Sparse curly hair* - **Sparse, curly, or unruly hair** is a common dermatological finding across various RASopathies, including **Noonan syndrome** and **Costello syndrome**. - It results from the dysregulation of the **RAS/MAPK signaling pathway**, which plays a crucial role in hair follicle development. *Distinct craniofacial features* - Many RASopathies are characterized by **distinct craniofacial dysmorphisms**, such as broad forehead, hypertelorism, downward-slanting palpebral fissures, and low-set ears. - These features vary between specific syndromes (e.g., **Noonan syndrome**, **Costello syndrome**, **CFC syndrome**) but are a hallmark of the group. *Keratosis pilaris* - **Keratosis pilaris**, characterized by small, rough bumps (often on the upper arms, thighs, and buttocks), is a frequently observed dermatologic manifestation in several RASopathies. - It is thought to be related to the underlying **RAS/MAPK pathway dysfunction**, which influences keratinization and follicular development. *Palmoplantar hyperkeratosis* - **Palmoplantar hyperkeratosis** (thickening of skin on palms and soles) is a prominent feature of **Costello syndrome**, one of the RASopathies. - It typically develops in early childhood and is considered a characteristic dermatologic manifestation of this condition. - This feature helps distinguish Costello syndrome from other RASopathies.

Question 114: If a baby has a XX or XY genotype, normal internal gonads, but ambiguous external genitalia, it is called?

A. True hermaphrodite
B. Disorder of Sex Development (DSD) (Correct Answer)
C. Intersex (outdated term)
D. Any of the above
E. Pseudohermaphrodite

Explanation: ***Disorder of Sex Development (DSD)*** - This is the **current preferred medical terminology** that encompasses conditions where there is a discrepancy between chromosomal sex, gonadal sex, and anatomical sex. - The scenario described—normal XX or XY genotype and normal internal gonads with **ambiguous external genitalia**—fits the definition of a DSD. - This **umbrella term** has replaced older terminology and is the most appropriate answer in modern medical practice. *True hermaphrodite* - A true hermaphrodite, now referred to as **ovotesticular DSD**, possesses both ovarian and testicular tissue simultaneously. - The question specifies **normal internal gonads** (either ovaries or testes, not both), which excludes this diagnosis. *Intersex (outdated term)* - While "intersex" was historically used to describe individuals with atypical sexual characteristics, it is now considered an **outdated and less precise** term in medical contexts. - "Disorder of Sex Development" is the preferred and more comprehensive medical classification. *Pseudohermaphrodite* - This was the **classical medical term** for exactly this presentation: normal chromosomal sex and appropriate internal gonads but ambiguous external genitalia. - Examples include 46,XX DSD with virilization (e.g., **congenital adrenal hyperplasia**) or 46,XY DSD with undervirilization (e.g., **androgen insensitivity syndrome**). - This term has been **replaced by DSD terminology** in modern medical practice to avoid stigmatizing language. *Any of the above* - While multiple terms have been used historically, **DSD is the most accurate and currently accepted medical term** for this specific presentation. - Therefore, this option is incorrect as it suggests all answers are equally valid.

Question 115: A 6-month-old child presented with multiple episodes of seizures over the past 2.5 months. The child was admitted to the ward and had frequent episodes of hypoglycemia, which precipitated the seizures. On examination, hepatosplenomegaly, short stature, thin extremities, and a doll-like facies were noted. Laboratory findings revealed hyperuricemia, lactic acidosis, and hyperlipidemia. Which enzyme deficiency is responsible for this disorder?

A. Glucose-6-phosphatase (Correct Answer)
B. Acid maltase
C. Phosphofructokinase deficiency
D. Debranching enzyme deficiency
E. Branching enzyme

Explanation: ***Glucose-6-phosphatase*** - This enzyme deficiency leads to **Von Gierke's disease (Type I glycogen storage disease)**, characterized by severe **fasting hypoglycemia** due to the inability to release glucose from glycogen stores or perform gluconeogenesis. - The accumulation of glucose-6-phosphate shunts substrates towards **lactic acid**, **uric acid**, and **lipid** synthesis, explaining the **lactic acidosis, hyperuricemia, hyperlipidemia**, and resultant **hepatosplenomegaly** and **doll-like facies**. *Acid maltase* - This refers to **Pompe disease (Type II glycogen storage disease)**, which primarily affects **cardiac and skeletal muscles**, leading to **cardiomyopathy** and muscle weakness. - While it involves glycogen storage, **hypoglycemia** and the metabolic derangements seen in the patient (e.g., hyperuricemia, lactic acidosis) are **not characteristic features**. *Phosphofructokinase deficiency* - This is **Tarui disease (Type VII glycogen storage disease)**, a rare disorder affecting **muscle and red blood cells**, causing **exercise intolerance**, muscle pain, and hemolytic anemia. - While it affects glycolysis, it **does not typically present with severe hypoglycemia** or the specific metabolic characteristics like hyperuricemia and lactic acidosis noted in the child. *Debranching enzyme deficiency* - This is **Cori disease (Type III glycogen storage disease)**, which results in milder hypoglycemia, hepatomegaly, and myopathy. - The deficiency leads to the accumulation of **glycogen with short outer branches**, but the severe and persistent metabolic derangements (marked lactic acidosis, hyperuricemia) and consistent severe hypoglycemia described are **less characteristic** than in Von Gierke's disease. *Branching enzyme* - This is **Andersen disease (Type IV glycogen storage disease)**, a rare disorder characterized by **progressive liver cirrhosis** and **hepatosplenomegaly** starting in infancy. - Unlike Von Gierke's disease, it **does not present with hypoglycemia** as the primary feature, and the metabolic profile (hyperuricemia, lactic acidosis, hyperlipidemia) is **not typical**.

Question 116: Which of the following is not a usual feature of Noonan syndrome?

A. Webbed neck
B. Short stature
C. Infertility
D. Intellectual disability (Correct Answer)
E. Pulmonary stenosis

Explanation: ***Intellectual disability*** - While some individuals with **Noonan syndrome** may have mild learning difficulties, **significant intellectual disability** is not a typical or defining feature of the condition. - The spectrum of cognitive abilities in Noonan syndrome ranges from normal to mild learning challenges. *Webbed neck* - A **webbed neck** due to excess skin folds is a common dysmorphic feature in Noonan syndrome, similar to Turner syndrome. - This is an important diagnostic clue, contributing to the characteristic gestalt of the syndrome. *Infertility* - Both males and females with Noonan syndrome can experience **infertility** or subfertility, often due to gonadal dysfunction such as **cryptorchidism** in males and ovarian insufficiency in females. - **Cryptorchidism** (undescended testes) is particularly common and can impact fertility. *Short stature* - **Short stature** is a very common and characteristic feature of Noonan syndrome, often evident from childhood. - Growth hormone deficiency can contribute to the growth failure seen in these individuals. *Pulmonary stenosis* - **Pulmonary stenosis** is the most common cardiac defect in Noonan syndrome, occurring in approximately **50-60%** of affected individuals. - Other cardiac abnormalities may include hypertrophic cardiomyopathy and atrial septal defects.

Question 117: Which condition is primarily associated with an abnormality of the X chromosome?

A. Turner's syndrome (Correct Answer)
B. Edward syndrome
C. Patau syndrome
D. Klinefelter syndrome
E. Down syndrome

Explanation: ***Turner's syndrome*** - **Turner's syndrome** is a genetic condition caused by the **absence of all or part of one X chromosome** in females (45, XO). - This X chromosome abnormality leads to characteristics such as **short stature**, ovarian dysgenesis, and a webbed neck. *Edward syndrome* - **Edward syndrome** is caused by the presence of an extra copy of chromosome 18 (trisomy 18), not an X chromosome abnormality. - It is associated with severe developmental delays, micrognathia, and **rocker-bottom feet**. *Patau syndrome* - **Patau syndrome** results from an extra copy of chromosome 13 (trisomy 13), not an abnormality of the X chromosome. - It is characterized by severe intellectual disability, **cleft lip and palate**, and polydactyly. *Down syndrome* - **Down syndrome** is caused by an extra copy of chromosome 21 (trisomy 21), not an X chromosome abnormality. - It is the most common chromosomal disorder, characterized by intellectual disability, **characteristic facial features**, and increased risk of congenital heart defects. *Klinefelter syndrome* - **Klinefelter syndrome** is a genetic condition in males with an extra X chromosome (47, XXY), which is an X chromosome abnormality, but it is not the **primary** condition *exclusively* associated with an X abnormality among the given choices, as Turner's is due to a *missing* X chromosome. - This condition leads to characteristics such as **tall stature**, underdeveloped testes, and gynecomastia.

Question 118: A four-year-old child presents with a large face, large jaw, large ears, and macroorchidism. What is the most likely diagnosis?

A. Down syndrome
B. Cri du chat syndrome
C. Fragile X syndrome (Correct Answer)
D. McCune-Albright syndrome
E. Klinefelter syndrome

Explanation: ***Fragile X syndrome*** - This syndrome is characterized by **macroorchidism** (enlarged testes) and distinct facial features such as a **large face**, **prominent jaw**, and **large ears**. - It is an X-linked dominant disorder caused by a **FMR1 gene mutation** leading to an increased number of CGG trinucleotide repeats. *Down syndrome* - Characterized by **upslanting palpebral fissures**, **epicanthic folds**, a **flat nasal bridge**, and a **single palmar crease**, which are not described here. - While associated with intellectual disability, it does not present with macroorchidism or the specific facial features mentioned. *Cri du chat syndrome* - This syndrome is known for a distinctive **high-pitched cry** resembling a cat's meow in infancy, along with **microcephaly** and **hypertelorism**. - It results from a deletion on the **short arm of chromosome 5** and does not typically present with macroorchidism or a large jaw. *McCune-Albright syndrome* - This syndrome is characterized by a triad of **fibrous dysplasia of bone**, **café-au-lait spots** (irregularly shaped hyperpigmented skin lesions), and **precocious puberty**. - It is caused by a somatic mutation in the **GNAS gene** and does not involve the specific facial features or macroorchidism described. *Klinefelter syndrome* - This syndrome (47,XXY) presents with **tall stature**, **gynecomastia**, and **small, firm testes** (not macroorchidism), typically noted after puberty. - Patients may have mild developmental delay but lack the distinctive facial features (large jaw, large ears) seen in this case.

Question 119: Which of the following statements is true regarding Turner syndrome?

A. Individuals typically have normal height and growth patterns.
B. Intelligence is typically normal. (Correct Answer)
C. Breast development is typically normal and occurs at the expected age.
D. Individuals have normal functioning ovaries throughout their reproductive years.
E. Cardiovascular anomalies are rarely associated with the condition.

Explanation: ***Intelligence is typically normal*** - Individuals with **Turner syndrome** generally have **normal intelligence** but may experience specific **neurocognitive deficits**, such as difficulties with visual-spatial tasks or nonverbal learning. - While they may require **specialized educational support** for these challenges, their overall cognitive abilities usually fall within the average range. *Individuals typically have normal height and growth patterns* - A hallmark feature of Turner syndrome is **short stature**, which is due to the haploinsufficiency of the **SHOX gene**. - **Growth hormone therapy** is often initiated in childhood to improve adult height outcomes. *Breast development is typically normal and occurs at the expected age* - Due to **gonadal dysgenesis** (non-functional ovaries), individuals with Turner syndrome experience **primary amenorrhea** and **lack of breast development** unless estrogen replacement therapy is initiated. - **Estrogen deficiency** prevents the typical pubertal changes associated with feminization. *Individuals have normal functioning ovaries throughout their reproductive years* - A defining characteristic of Turner syndrome is **gonadal dysgenesis**, meaning the ovaries are non-functional **streak gonads**. - This leads to **infertility** and **primary ovarian insufficiency** from birth, requiring hormone replacement for secondary sexual characteristic development. *Cardiovascular anomalies are rarely associated with the condition* - **Cardiovascular defects** occur in approximately **30-50%** of individuals with Turner syndrome, making them a common and clinically significant feature. - The most frequent cardiac anomalies include **bicuspid aortic valve** (30%), **coarctation of the aorta** (10-15%), and **aortic dilation**. - Regular **cardiovascular screening** with echocardiography is recommended throughout life due to increased risk of aortic dissection.

Question 120: Sweat chlorides are increased in:

A. Cystic fibrosis (Correct Answer)
B. Addison's disease
C. Conn's syndrome
D. Phaeochromocytoma
E. Hypothyroidism

Explanation: ***Cystic fibrosis*** - **Cystic fibrosis** is characterized by a defect in the **cystic fibrosis transmembrane conductance regulator (CFTR) protein**, which is responsible for chloride transport. - This defect leads to impaired reabsorption of chloride in sweat glands, resulting in characteristically **elevated sweat chloride levels** (usually >60 mEq/L), which is the basis for the **sweat chloride test** used for diagnosis. *Addison's disease* - **Addison's disease** (adrenal insufficiency) primarily affects mineralocorticoid and glucocorticoid production, leading to **hyponatremia** and **hyperkalemia**, but not directly affecting sweat chloride concentration in a diagnostically significant way. - Patients may experience dehydration and salt craving, but their sweat chloride levels are not used for diagnosis. *Conn's syndrome* - **Conn's syndrome** is characterized by primary **hyperaldosteronism**, leading to sodium retention and potassium excretion, often causing **hypertension** and **hypokalemia**. - It does not involve a defect in sweat gland chloride transport and therefore does not cause increased sweat chlorides. *Phaeochromocytoma* - A **phaeochromocytoma** is a tumor of the adrenal medulla that secretes excessive **catecholamines**, leading to symptoms like **hypertension**, palpitations, and sweating. - While excessive sweating can occur due to sympathetic overactivity, the chloride concentration in the sweat itself is not diagnostically elevated. *Hypothyroidism* - **Hypothyroidism** is characterized by decreased thyroid hormone production, leading to symptoms like **fatigue**, **weight gain**, **cold intolerance**, and **dry skin**. - It does not affect chloride transport in sweat glands and does not cause elevated sweat chloride levels.

Question 121: A 2-year-old child is brought by parents with a history of seizures and developmental delay, and he has multiple hypopigmented macules over the back. What is the most probable diagnosis?

A. Neurofibromatosis type 1
B. Tuberous sclerosis (Correct Answer)
C. Sturge weber's syndrome
D. Linear Sebaceous nevus syndrome
E. Hypomelanosis of Ito

Explanation: ***Tuberous sclerosis*** - The classic triad of **seizures**, **developmental delay**, and **hypopigmented macules** (ash-leaf spots) is highly suggestive of tuberous sclerosis. - This condition is an **autosomal dominant neurocutaneous disorder** characterized by the formation of **hamartomas** in various organs, including the brain, skin, kidneys, and heart. *Neurofibromatosis type 1* - Characterized by **multiple café-au-lait spots**, **axillary/inguinal freckling**, and **neurofibromas**. - While seizures and developmental delay can occur, the presence of **hypopigmented macules** points away from NF1. *Sturge weber's syndrome* - Presents with a **port-wine stain** (facial cutaneous angioma) in the distribution of the trigeminal nerve. - Associated with **leptomeningeal angioma**, leading to seizures and neurological deficits, but not with hypopigmented macules. *Linear Sebaceous nevus syndrome* - Involves a **large sebaceous nevus** (usually on the face or scalp) in association with **CNS abnormalities** (e.g., seizures, developmental delay) and other systemic findings. - The hallmark skin lesion is a **yellow-orange, waxy nevus**, not hypopigmented macules. *Hypomelanosis of Ito* - Characterized by **hypopigmented whorled streaks or patches** along the lines of Blaschko. - Can be associated with seizures and developmental delay, but the key distinguishing feature is the **bilateral whorled pattern** rather than discrete oval ash-leaf spots seen in tuberous sclerosis.

Question 122: Duchenne muscular dystrophy is inherited as:

A. Autosomal dominant
B. Autosomal recessive
C. X-linked recessive (Correct Answer)
D. X-linked dominant
E. Mitochondrial inheritance

Explanation: ***X-linked recessive*** - Duchenne muscular dystrophy is primarily due to mutations in the **dystrophin gene**, located on the X chromosome, leading to X-linked recessive inheritance [1]. - Males are predominantly affected due to the presence of a single X chromosome, while females are carriers and may show mild symptoms [2]. *Autosomal dominant* - This mode of inheritance involves only one copy of a mutated gene for the condition to manifest, which is not the case for Duchenne muscular dystrophy. - Autosomal dominant disorders typically have a **vertical inheritance pattern**, unlike the skipped generations seen with X-linked recessive traits [2]. *X-linked dominant* - In X-linked dominant conditions, both males and females can be affected, which contrasts with the severe male predominance observed in Duchenne muscular dystrophy cases. - Female carriers of X-linked dominant disorders often experience more severe symptoms, which is not typical for this condition where females are usually asymptomatic carriers. *Autosomal recessive* - Autosomal recessive disorders require both copies of a gene to be mutated for the condition to be expressed, differing from the one-gene involvement in X-linked recessive disorders. - Conditions that follow this pattern often arise in families with a history of consanguinity, which is not the primary inheritance scenario for Duchenne muscular dystrophy. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1244-1245. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, p. 151.

Question 123: Which of the following conditions is characterized by webbing of the neck, short stature, increased carrying angle, low posterior hairline, primary amenorrhea, and short fourth metacarpal?

A. Klinefelter syndrome
B. Turner syndrome (Correct Answer)
C. Cri-du-chat syndrome
D. Noonan syndrome
E. Down syndrome

Explanation: ***Turner syndrome*** - Characterized by **webbing of the neck**, **short stature**, and **primary amenorrhea**, which are classic features of Turner syndrome [1][2]. - The presence of a **short fourth metacarpal** is also a specific skeletal manifestation associated with this condition. - **Short stature** in Turner syndrome is specifically explained by haploinsufficiency of the SHOX gene [1]. *Noonan syndrome* - Presents with features like **short stature** and **cardiac anomalies**, but lacks the specific manifestations of neck webbing and primary amenorrhea. - Typically associated with facial dysmorphisms, such as **widely spaced eyes** and a **distinctive appearance** which are not mentioned here. *Klinefelter syndrome* - Characterized by **47,XXY** karyotype leading to **gynecomastia** and **testicular atrophy**, rather than symptoms like webbed neck or short stature. - Men with this syndrome usually display **delayed or incomplete puberty**, not primary amenorrhea. *Cri-du-chat syndrome* - Primarily associated with a **distinctive high-pitched cry** and developmental delays, rather than physical traits like webbed neck or short fourth metacarpal. - Symptoms are more related to **chromosomal deletion** and do not include amenorrhea or features typical of Turner syndrome. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 175-177. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 173-174.

Question 124: Which of the following statements is true regarding cystic fibrosis?

A. Can present with meconium ileus in newborns. (Correct Answer)
B. Negative sweat test is diagnostic
C. Caused by mutations in the BRCA gene
D. Has equal incidence across all ethnic populations
E. Is inherited in an autosomal dominant pattern

Explanation: ***Can present with meconium ileus in newborns*** - **Meconium ileus**, an obstruction of the small intestine by thickened meconium, is a classic initial presentation of **cystic fibrosis (CF)** in about 10-20% of affected newborns. - This symptom arises due to the **thick, sticky secretions** in the intestines, a hallmark of CF's impact on exocrine glands. *Negative sweat test is diagnostic* - A **negative sweat test** (salt concentration less than 30 mmol/L for infants, or 40 mmol/L for older children/adults) typically *rules out* cystic fibrosis, rather than confirming it. - A **positive sweat test** (typically >60 mmol/L chloride) is indicative of CF, but needs to be confirmed with **genetic testing**. *Caused by mutations in the BRCA gene* - Cystic fibrosis is caused by mutations in the **CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) gene**, which is responsible for chloride ion transport. - **BRCA genes** (BRCA1 and BRCA2) are associated with an increased risk of breast and ovarian cancers, and are completely unrelated to CF. *Has equal incidence across all ethnic populations* - CF has a **variable incidence** across different ethnic populations; it is most common in individuals of **Northern European descent**. - It is relatively rare in populations of African and Asian descent, demonstrating a clear ethnic predisposition rather than equal incidence. *Is inherited in an autosomal dominant pattern* - Cystic fibrosis is inherited in an **autosomal recessive pattern**, not autosomal dominant. - This means both parents must be carriers (or affected) for a child to have the disease; each pregnancy has a **25% chance** of producing an affected child when both parents are carriers. - In autosomal dominant conditions, only one mutated gene copy is needed to cause disease, which is not the case for CF.

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Inborn Errors of Metabolism

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Mitochondrial Disorders

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Multifactorial Inheritance Disorders

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Newborn Screening

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Single Gene Disorders

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