A 6-month-old baby boy presents to his pediatrician for the evaluation of recurrent bacterial infections. He is currently well but has already been hospitalized multiple times due to his bacterial infections. His blood pressure is 103/67 mm Hg and heart rate is 74/min. Physical examination reveals light-colored skin and silver hair. On examination of a peripheral blood smear, large cytoplasmic vacuoles containing microbes are found within the neutrophils. What diagnosis do these findings suggest?
Q52
A 4-year-old boy is brought by his parents to his pediatrician’s office. His mother mentions that the child has been producing an increased number of foul stools recently. His mother says that over the past year, he has had 1 or 2 foul-smelling stools per month. Lately, however, the stools are looser, more frequent, and have a distinct odor. Over the past several years, he has been admitted 4 times with episodes of pneumonia. Genetic studies reveal a mutation on a specific chromosome that has led to a 3 base-pair deletion for the amino acid phenylalanine. Which of the following chromosomes is the defective gene responsible for this boy’s clinical condition?
Q53
A 14-year-old boy is brought to the physician by his parents for a well-child visit. The patient was born at 38 weeks' gestation via vaginal delivery and has been healthy. He attends a junior high school and is having difficulties keeping up with his classmates in many classes. He is at the 97th percentile for height and 50th percentile for weight. Vital signs are within normal limits. Cardiac examination shows a high-frequency midsystolic click that is best heard at the left fifth intercostal space. The patient has long extremities along with excess breast tissue bilaterally. He has no axillary hair. Genital examination shows reduced scrotal size and a normal sized penis. Which of the following tests is the most likely to diagnose the patient's underlying disorder?
Q54
A 2-year-old girl presents to the pediatrician with an itchy rash. Her mother reports that she has had a crusty rash on the face and bilateral upper extremities intermittently for the past 2 months. The child's past medical history is notable for 3 similar episodes of severely itchy rashes since birth. She has also had 2 non-inflamed abscesses on her arms over the past year. Her temperature is 98.9°F (37.2°C), blood pressure is 108/68 mmHg, pulse is 94/min, and respirations are 18/min. On exam, she appears uncomfortable and is constantly itching her face and arms. There is an eczematous rash on the face and bilateral upper extremities. Her face has thickened skin with a wide-set nose. This patient's condition is most likely caused by a mutation in which of the following genes?
Q55
A 2-year-old boy is brought to the physician because of a productive cough for 5 days. He has a history of recurrent lower respiratory tract infections and sinusitis treated with oral antibiotics. He frequently has loose stools that do not flush easily. He was born at 37 weeks' gestation and the neonatal period was complicated by meconium ileus. His immunizations are up-to-date. He is at the 15th percentile for height and at the 5th percentile for weight. His temperature is 37.1°C (98.8°F), pulse is 98/min, and respirations are 38/min. Pulse oximetry on room air shows an oxygen saturation of 95%. Examination shows bilateral nasal polyps. There are scattered inspiratory crackles heard in the thorax. Further evaluation of this patient is most likely to show which of the following?
Q56
A 4-week-old Caucasian baby presents for a routine checkup. The patient was born to a 28-year-old G1P1 woman at 38 weeks estimated gestational age by cesarean section secondary to breech presentation. The pregnancy was complicated by gestational diabetes, which the mother controlled with diet and exercise. Prenatal ultrasounds showed normal fetal anatomy. Both parents are nonsmokers. The vital signs include: temperature 37.0°C (98.6°F), blood pressure 85/45 mm Hg, pulse 140/min, respiratory rate 42/min, and oxygen saturation 99% on room air. Height, weight, and head circumference are within the 90th percentile. Positive Moro and Babinski reflexes are present. The cardiopulmonary examination is normal. While in the supine position, the left leg is visibly shortened relative to the right. When the left hip is abducted with pressure applied to the greater trochanter of the femur, there is a non-tender clunking sound elicited. There is asymmetry of the gluteal skin folds. A blue macule is noted over the sacral region. Which of the following is the most appropriate next step in the management of this patient?
Q57
A 5-year-old boy is brought to a pediatrician by his parents for evaluation of learning difficulties in school. He has short stature, a flat face, low-set ears, a large tongue, and a single line on the palm. He was born to his parents after 20 years of marriage. You ordered karyotyping which will likely reveal which of the following?
Q58
A 9-month-old female infant is brought in by her mother to the pediatrician because she is concerned that her daughter is not growing normally. On physical exam, the head circumference is 95th percentile and the height is 5th percentile. The child has disproportionate growth such that both the upper and lower extremities show a rhizomelic pattern of shortening, but the axial skeleton appears to be normal. The child appears to have normal intelligence, but has delayed motor milestones; specifically, she is not able to roll or sit up by herself. Which of the following best describes the mode of inheritance for this disorder?
Q59
A 17-year-old boy is brought to the pediatrician by his mother for an initial visit. He recently immigrated from Cambodia. Through an interpreter, the patient reports 6 months of mild exertional dyspnea. He denies chest pain or palpitations. His medical history is unremarkable and he has never had any surgeries. His family history is significant for hypertension and diabetes. His father died of tuberculosis. The patient’s vaccination history is unknown. His temperature is 98°F (36.7°C), blood pressure is 113/71 mmHg, and pulse is 82/min. His BMI is 24 kg/m^2. Physical examination shows a well-nourished, cooperative boy without any grossly dysmorphic features. Cardiac auscultation reveals a grade II systolic ejection murmur along the left upper sternal border and a mid-diastolic rumble along the left sternal border. S1 is normal and the splitting of S2 does not change with inspiration. Which of the following is the most likely diagnosis?
Q60
An 11-month-old boy is brought to the emergency department because of intermittent episodes of inconsolable crying for 4 hours. The parents report that the patient does not appear to be in discomfort between episodes, and moves and plays normally. The episodes have occurred at roughly 15-minute intervals and have each lasted a few minutes before subsiding. He has also vomited 3 times since these episodes began. The first vomitus appeared to contain food while the second and third appeared pale green in color. The patient was born at term and has been healthy. His immunizations are up-to-date. He has no history of recent travel. His older brother has Crohn's disease. The patient is at 50th percentile for height and 60th percentile for weight. He does not appear to be in acute distress. His temperature is 37.1°C (98.8°F), pulse is 125/min, respirations are 36/min, and blood pressure is 85/40 mm Hg. During the examination, the patient begins to cry and draws his knees up to his chest. Shortly thereafter, he passes stool with a mixture of blood and mucous; the patient's discomfort appears to resolve. Abdominal examination shows a sausage-shaped abdominal mass in the right upper quadrant. Which of the following is the most appropriate next step in the management of this patient?
Congenital defects US Medical PG Practice Questions and MCQs
Question 51: A 6-month-old baby boy presents to his pediatrician for the evaluation of recurrent bacterial infections. He is currently well but has already been hospitalized multiple times due to his bacterial infections. His blood pressure is 103/67 mm Hg and heart rate is 74/min. Physical examination reveals light-colored skin and silver hair. On examination of a peripheral blood smear, large cytoplasmic vacuoles containing microbes are found within the neutrophils. What diagnosis do these findings suggest?
A. Leukocyte adhesion deficiency-1
B. Common variable immunodeficiency
C. Acquired immunodeficiency syndrome
D. Chediak-Higashi syndrome (Correct Answer)
E. Congenital thymic aplasia
Explanation: **Chediak-Higashi syndrome**
- The presence of **recurrent bacterial infections**, **light-colored skin and silver hair**, and **large cytoplasmic vacuoles within neutrophils** is pathognomonic for Chediak-Higashi syndrome.
- This condition is an **autosomal recessive disorder** characterized by impaired lysosomal trafficking, affecting phagocyte function and melanosome formation.
*Leukocyte adhesion deficiency-1*
- This disorder is characterized by **recurrent bacterial infections** due to a defect in integrins, preventing neutrophils from adhering to endothelial cells and migrating to infection sites.
- However, it typically presents with **delayed umbilical cord separation** and lacks the distinctive features of light-colored skin/silver hair and giant cytoplasmic granules.
*Common variable immunodeficiency*
- This condition is characterized by **recurrent bacterial infections** due to low levels of immunoglobulins, leading to impaired B-cell function.
- It typically presents later in childhood or adulthood and does not involve abnormalities in skin pigmentation or neutrophil morphology.
*Acquired immunodeficiency syndrome*
- **AIDS** is caused by the **Human Immunodeficiency Virus (HIV)** and leads to a progressive decline in CD4+ T cells, resulting in opportunistic infections.
- While it causes recurrent infections, the clinical presentation in a **6-month-old infant** with silver hair and giant neutrophil granules is not consistent with AIDS unless there's a strong perinatal exposure history, which is not mentioned.
*Congenital thymic aplasia*
- Also known as **DiGeorge syndrome**, this condition involves **T-cell immunodeficiency** due to hypoplasia or aplasia of the thymus, leading to recurrent viral, fungal, and parasitic infections.
- It is also associated with **hypocalcemia** and **congenital heart defects**, but it does not present with recurrent bacterial infections combined with light skin/silver hair and giant neutrophil granules.
Question 52: A 4-year-old boy is brought by his parents to his pediatrician’s office. His mother mentions that the child has been producing an increased number of foul stools recently. His mother says that over the past year, he has had 1 or 2 foul-smelling stools per month. Lately, however, the stools are looser, more frequent, and have a distinct odor. Over the past several years, he has been admitted 4 times with episodes of pneumonia. Genetic studies reveal a mutation on a specific chromosome that has led to a 3 base-pair deletion for the amino acid phenylalanine. Which of the following chromosomes is the defective gene responsible for this boy’s clinical condition?
A. Chromosome 4
B. Chromosome 7 (Correct Answer)
C. Chromosome 22
D. Chromosome 17
E. Chromosome 15
Explanation: ***Chromosome 7***
- This patient's symptoms (recurrent pneumonia, foul-smelling stools/steatorrhea) are classic for **cystic fibrosis (CF)**. The most common mutation in CF is a **3-base pair deletion for phenylalanine** (ΔF508), located on the **CFTR gene** on **chromosome 7**.
- The cystic fibrosis transmembrane conductance regulator (CFTR) gene, which is defective in CF, is found on **the long arm (q) of chromosome 7** at position 31.2.
*Chromosome 4*
- **Chromosome 4** is associated with genetic disorders such as **Huntington's disease** and **Wolf-Hirschhorn syndrome**, which do not match the clinical presentation of recurrent pneumonia and steatorrhea.
- Huntington's disease involves trinucleotide repeats and primarily affects neurological function later in life.
*Chromosome 22*
- **Chromosome 22** is implicated in conditions like **DiGeorge syndrome** (22q11.2 deletion syndrome) and certain leukemias, none of which present with the described gastrointestinal and pulmonary symptoms.
- DiGeorge syndrome is characterized by cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, and hypocalcemia.
*Chromosome 17*
- **Chromosome 17** is associated with diseases such as **Neurofibromatosis type 1** and **hereditary breast and ovarian cancer** (BRCA1 gene), which are inconsistent with the patient's symptoms.
- Neurofibromatosis type 1 primarily involves the skin, nervous system, and bones, with manifestations like café-au-lait spots and neurofibromas.
*Chromosome 15*
- **Chromosome 15** is linked to disorders like **Prader-Willi syndrome** and **Angelman syndrome**, which are distinct neurodevelopmental disorders not characterized by recurrent respiratory infections and malabsorption.
- These syndromes result from genomic imprinting defects and present with intellectual disability, developmental delay, and specific physical features.
Question 53: A 14-year-old boy is brought to the physician by his parents for a well-child visit. The patient was born at 38 weeks' gestation via vaginal delivery and has been healthy. He attends a junior high school and is having difficulties keeping up with his classmates in many classes. He is at the 97th percentile for height and 50th percentile for weight. Vital signs are within normal limits. Cardiac examination shows a high-frequency midsystolic click that is best heard at the left fifth intercostal space. The patient has long extremities along with excess breast tissue bilaterally. He has no axillary hair. Genital examination shows reduced scrotal size and a normal sized penis. Which of the following tests is the most likely to diagnose the patient's underlying disorder?
A. Urinalysis
B. Southern blot
C. Slit-lamp examination
D. Karyotyping (Correct Answer)
E. Serum IGF-1 measurement
Explanation: ***Karyotyping***
- The patient's presentation with **tall stature**, **long extremities**, **gynecomastia**, **small testes**, and **learning difficulties** is highly suggestive of **Klinefelter syndrome (47,XXY)**.
- **Karyotyping** is the definitive diagnostic test for Klinefelter syndrome as it identifies the presence of an extra X chromosome.
*Urinalysis*
- This test is used to detect various kidney and urinary tract conditions and would not identify a **chromosomal abnormality**.
- While it can reveal issues like **proteinuria** or **hematuria**, these are not consistent with the primary presenting symptoms.
*Southern blot*
- This technique detects specific **DNA sequences** and is used for conditions like **fragile X syndrome** or **gene deletions**, but it is not the primary diagnostic tool for **aneuploidies** like Klinefelter syndrome.
- Karyotyping provides a broader overview of the entire **chromosome set**, which is necessary to identify an extra chromosome.
*Slit-lamp examination*
- This examination is used to visualize the eyes and is relevant for conditions like **Marfan syndrome** (**ectopia lentis**) or other ocular abnormalities, which are not the primary concern here.
- There are no symptoms presented that would suggest the need for a **slit-lamp examination**.
*Serum IGF-1 measurement*
- **Insulin-like growth factor 1 (IGF-1)** is measured to assess **growth hormone levels** and diagnose conditions like **acromegaly** or **dwarfism**.
- While the patient is tall, his other features (gynecomastia, small testes, learning difficulties) point strongly to a **chromosomal disorder** rather than a primary growth hormone abnormality.
Question 54: A 2-year-old girl presents to the pediatrician with an itchy rash. Her mother reports that she has had a crusty rash on the face and bilateral upper extremities intermittently for the past 2 months. The child's past medical history is notable for 3 similar episodes of severely itchy rashes since birth. She has also had 2 non-inflamed abscesses on her arms over the past year. Her temperature is 98.9°F (37.2°C), blood pressure is 108/68 mmHg, pulse is 94/min, and respirations are 18/min. On exam, she appears uncomfortable and is constantly itching her face and arms. There is an eczematous rash on the face and bilateral upper extremities. Her face has thickened skin with a wide-set nose. This patient's condition is most likely caused by a mutation in which of the following genes?
A. STAT3 (Correct Answer)
B. IL-12 receptor
C. WAS
D. LYST
E. Adenosine deaminase
Explanation: ***STAT3***
- The patient's presentation with recurrent **abscesses**, widespread eczematous rash, and characteristic facial features (thickened skin, wide-set nose) is highly suggestive of **Job syndrome**, also known as hyper-IgE syndrome.
- Job syndrome is an autosomal dominant primary immunodeficiency caused by mutations in the **STAT3 gene**, leading to impaired Th17 cell function and recurrent infections, particularly with *Staphylococcus aureus*.
*IL-12 receptor*
- Mutations in the **IL-12 receptor** lead to a predisposition to infections with intracellular bacteria and mycobacteria (e.g., disseminated atypical mycobacterial infections, salmonella) due to impaired Th1 immune response.
- This condition is not typically associated with recurrent abscesses, eczematous rashes, or the specific facial features seen in this patient.
*WAS*
- Mutations in the **WAS gene** cause Wiskott-Aldrich syndrome, characterized by the triad of **thrombocytopenia** (leading to bleeding diathesis), **eczema**, and recurrent infections.
- While eczema is present in the patient, the absence of thrombocytopenia and the presence of recurrent abscesses and specific facial features make Wiskott-Aldrich syndrome less likely.
*LYST*
- Mutations in the **LYST gene** cause Chédiak-Higashi syndrome, an autosomal recessive disorder characterized by partial **oculocutaneous albinism**, recurrent pyogenic infections, and neurological abnormalities.
- The patient's presentation does not include albinism or significant neurological findings, nor the giant lysosomes characteristic of this syndrome.
*Adenosine deaminase*
- Deficiency of **adenosine deaminase (ADA)** leads to severe combined immunodeficiency (SCID), a profound impairment of both T and B cell immunity.
- Patients typically present with severe, life-threatening infections, chronic diarrhea, and failure to thrive early in life, a much more severe and generalized immunodeficiency than described in this patient.
Question 55: A 2-year-old boy is brought to the physician because of a productive cough for 5 days. He has a history of recurrent lower respiratory tract infections and sinusitis treated with oral antibiotics. He frequently has loose stools that do not flush easily. He was born at 37 weeks' gestation and the neonatal period was complicated by meconium ileus. His immunizations are up-to-date. He is at the 15th percentile for height and at the 5th percentile for weight. His temperature is 37.1°C (98.8°F), pulse is 98/min, and respirations are 38/min. Pulse oximetry on room air shows an oxygen saturation of 95%. Examination shows bilateral nasal polyps. There are scattered inspiratory crackles heard in the thorax. Further evaluation of this patient is most likely to show which of the following?
A. Elevated prothrombin time (Correct Answer)
B. Decreased residual volume on spirometry
C. Cytoplasmic anti-neutrophil cytoplasmic antibodies
D. Metabolic acidosis
E. Glutamic acid decarboxylase antibodies
Explanation: ***Elevated prothrombin time***
- This patient's presentation is highly suggestive of **cystic fibrosis**, characterized by recurrent respiratory infections, **malabsorption** (loose, foul-smelling stools, failure to thrive), and a history of **meconium ileus**.
- **Malabsorption** in cystic fibrosis leads to deficiencies of **fat-soluble vitamins** (A, D, E, K). **Vitamin K deficiency** impairs the synthesis of clotting factors II, VII, IX, and X, leading to a **prolonged prothrombin time (PT)**.
*Decreased residual volume on spirometry*
- Patients with cystic fibrosis often develop **obstructive lung disease** due to thick mucus, leading to **air trapping** and subsequent **increased residual volume** on spirometry, not decreased.
- Decreased residual volume is typically associated with **restrictive lung diseases**, which are not characteristic of early cystic fibrosis.
*Cytoplasmic anti-neutrophil cytoplasmic antibodies*
- **c-ANCA** (cytoplasmic anti-neutrophil cytoplasmic antibodies) are associated with **granulomatosis with polyangiitis (Wegener's)**, a vasculitic condition, and are not typically found in cystic fibrosis.
- While cystic fibrosis can cause chronic inflammation, the specific autoantibodies for vasculitis are not characteristic.
*Metabolic acidosis*
- While severe lung disease can lead to **respiratory acidosis** (due to CO2 retention), metabolic acidosis is not a primary or typical feature of cystic fibrosis itself.
- In cases of severe dehydration or other complications, metabolic acidosis could occur, but it's not a defining characteristic of the chronic disease.
*Glutamic acid decarboxylase antibodies*
- **Glutamic acid decarboxylase (GAD) antibodies** are markers for **Type 1 diabetes mellitus**, an autoimmune condition affecting pancreatic beta cells.
- While diabetes can be a complication of cystic fibrosis (cystic fibrosis-related diabetes), GAD antibodies are not a direct finding in cystic fibrosis itself, nor are they the most immediate or common complication at this age.
Question 56: A 4-week-old Caucasian baby presents for a routine checkup. The patient was born to a 28-year-old G1P1 woman at 38 weeks estimated gestational age by cesarean section secondary to breech presentation. The pregnancy was complicated by gestational diabetes, which the mother controlled with diet and exercise. Prenatal ultrasounds showed normal fetal anatomy. Both parents are nonsmokers. The vital signs include: temperature 37.0°C (98.6°F), blood pressure 85/45 mm Hg, pulse 140/min, respiratory rate 42/min, and oxygen saturation 99% on room air. Height, weight, and head circumference are within the 90th percentile. Positive Moro and Babinski reflexes are present. The cardiopulmonary examination is normal. While in the supine position, the left leg is visibly shortened relative to the right. When the left hip is abducted with pressure applied to the greater trochanter of the femur, there is a non-tender clunking sound elicited. There is asymmetry of the gluteal skin folds. A blue macule is noted over the sacral region. Which of the following is the most appropriate next step in the management of this patient?
A. Observation with follow-up in 6 months
B. Magnetic resonance image (MRI) of the lumbosacral spine
C. Ultrasound of the hips (Correct Answer)
D. Ultrasound of the lumbosacral spine
E. X-ray of the hips
Explanation: **Ultrasound of the hips**
- The clinical findings of **leg length discrepancy**, **asymmetrical gluteal folds**, and a **palpable clunk** (consistent with an **Ortolani sign**) are highly suggestive of **developmental dysplasia of the hip (DDH)**.
- An **ultrasound of the hips** is the most appropriate initial diagnostic imaging modality for DDH in infants younger than 4-6 months because their femoral heads are primarily cartilaginous and not yet ossified, making X-rays less informative.
*Observation with follow-up in 6 months*
- Given the strong clinical signs of **DDH**, simple observation is **inappropriate** as early diagnosis and treatment are crucial to prevent long-term complications such as avascular necrosis and degenerative joint disease.
- Delaying diagnosis could lead to more invasive treatments and worse outcomes.
*Magnetic resonance image (MRI) of the lumbosacral spine*
- An MRI of the lumbosacral spine would be indicated for spinal cord abnormalities or other neurological concerns, which are **not suggested** by the patient's symptoms or physical examination findings.
- The present clinical picture points directly to a hip pathology.
*Ultrasound of the lumbosacral spine*
- An ultrasound of the lumbosacral spine is typically used to investigate **spinal dysraphism** or other spinal anomalies if there are cutaneous markers (e.g., sacral dimple, hairy patch) suggesting a spinal problem.
- While a **blue macule (Mongolian spot)** is noted, it is a benign finding and **not an indication** for spinal imaging in the absence of other neurological signs or deeper dimples/sinuses.
*X-ray of the hips*
- X-rays are **not effective** for diagnosing DDH in infants younger than 4-6 months because the **femoral head** is largely **cartilaginous** and not well-visualized on plain radiographs.
- X-rays become more useful after the femoral head ossification center develops, typically around 4-6 months of age.
Question 57: A 5-year-old boy is brought to a pediatrician by his parents for evaluation of learning difficulties in school. He has short stature, a flat face, low-set ears, a large tongue, and a single line on the palm. He was born to his parents after 20 years of marriage. You ordered karyotyping which will likely reveal which of the following?
A. 47, XXX
B. 47, XY, +18
C. 47, XXY
D. 45, XO
E. 47, XY, +21 (Correct Answer)
Explanation: ***47, XY, +21***
- The patient's presentation with **short stature**, a **flat face**, **low-set ears**, a **large tongue**, a **single palmar crease (Simian crease)**, and **learning difficulties** are classic diagnostic features of **Down syndrome**.
- **Down syndrome** is caused by the presence of an extra copy of chromosome 21, leading to a karyotype of **47, XY, +21** (if male) or 47, XX, +21 (if female). The mention of the parents' age (born after 20 years of marriage implies an older maternal age) is a significant risk factor for Down syndrome.
*47, XXX*
- This karyotype describes **Triple X syndrome**, which affects females. Individuals usually present with normal appearance, learning difficulties, and often do not have distinct physical features like those described in the case.
- The patient is a 5-year-old boy, immediately ruling out Triple X syndrome.
*47, XY, +18*
- This karyotype indicates **Edwards syndrome (Trisomy 18)**. While it presents with developmental delay and distinctive physical features, these typically include a **rocker-bottom feet**, **clenched hands**, and other severe abnormalities often leading to early demise.
- The specific features described in the patient, such as a **flat face** and **single palmar crease**, are not characteristic of Edwards syndrome.
*47, XXY*
- This karyotype describes **Klinefelter syndrome**, which affects males. This condition is characterized by **tall stature**, **hypogonadism**, and often **learning difficulties**, but the patient's features like **short stature**, **flat face**, and **single palmar crease** are not consistent with Klinefelter syndrome.
- The phenotype of Klinefelter syndrome becomes more evident in adolescence and adulthood.
*45, XO*
- This karyotype describes **Turner syndrome**, which affects females. Features include **short stature**, **webbed neck**, and **gonadal dysgenesis**.
- The patient is a 5-year-old boy, which rules out Turner syndrome.
Question 58: A 9-month-old female infant is brought in by her mother to the pediatrician because she is concerned that her daughter is not growing normally. On physical exam, the head circumference is 95th percentile and the height is 5th percentile. The child has disproportionate growth such that both the upper and lower extremities show a rhizomelic pattern of shortening, but the axial skeleton appears to be normal. The child appears to have normal intelligence, but has delayed motor milestones; specifically, she is not able to roll or sit up by herself. Which of the following best describes the mode of inheritance for this disorder?
A. Mitochondrial pattern of inheritance
B. X-linked recessive
C. Autosomal recessive
D. X-linked dominant
E. Autosomal dominant (Correct Answer)
Explanation: **Autosomal dominant**
- The clinical presentation with **rhizomelic dwarfism**, normal intelligence, and macrocephaly is highly suggestive of **achondroplasia**, which is inherited in an **autosomal dominant** pattern.
- Achondroplasia is caused by a mutation in the **fibroblast growth factor receptor 3 (FGFR3)** gene, which inhibits chondrocyte proliferation in the growth plate, leading to disproportionate short stature.
*Mitochondrial pattern of inheritance*
- This pattern is characterized by transmission only through the **mother** to all offspring, and typically affects tissues with high energy demands like muscle and brain due to impaired oxidative phosphorylation.
- The presented symptoms of disproportional dwarfism are not characteristic of common mitochondrial disorders.
*X-linked recessive*
- This pattern primarily affects **males**, with carrier mothers passing the trait to sons, and affected males not passing it to their sons.
- The described condition affects a female infant and the pattern of inheritance does not align with typical X-linked recessive disorders.
*Autosomal recessive*
- This pattern requires **two copies of the mutated gene** for the disease to manifest, meaning both parents are usually asymptomatic carriers.
- While some forms of dwarfism can be autosomal recessive, the specific clinical features and prevalence of achondroplasia point towards an autosomal dominant inheritance.
*X-linked dominant*
- This pattern affects both males and females, but often more severely in males, and affected fathers pass the trait to **all their daughters** but none of their sons.
- The symptoms described do not fit the typical presentation or inheritance pattern of X-linked dominant disorders, which are generally rarer for forms of skeletal dysplasia.
Question 59: A 17-year-old boy is brought to the pediatrician by his mother for an initial visit. He recently immigrated from Cambodia. Through an interpreter, the patient reports 6 months of mild exertional dyspnea. He denies chest pain or palpitations. His medical history is unremarkable and he has never had any surgeries. His family history is significant for hypertension and diabetes. His father died of tuberculosis. The patient’s vaccination history is unknown. His temperature is 98°F (36.7°C), blood pressure is 113/71 mmHg, and pulse is 82/min. His BMI is 24 kg/m^2. Physical examination shows a well-nourished, cooperative boy without any grossly dysmorphic features. Cardiac auscultation reveals a grade II systolic ejection murmur along the left upper sternal border and a mid-diastolic rumble along the left sternal border. S1 is normal and the splitting of S2 does not change with inspiration. Which of the following is the most likely diagnosis?
A. Atrial septal defect (Correct Answer)
B. Ventricular septal defect
C. Hypertrophic cardiomyopathy
D. Rheumatic heart disease
E. Bicuspid aortic valve
Explanation: ***Atrial septal defect***
- The patient presents with a **grade II systolic ejection murmur at the left upper sternal border** (pulmonic area due to increased flow across the pulmonic valve) and a **mid-diastolic rumble at the left sternal border** (tricuspid area due to increased flow across the tricuspid valve).
- The **fixed splitting of S2** (splitting of S2 that does not change with inspiration) is a classic auscultatory finding for an ASD due to persistent delay in pulmonic valve closure caused by a continuous overload of the right ventricle.
*Ventricular septal defect*
- The murmur of a VSD is typically a **holosystolic murmur** best heard at the **lower left sternal border**, not a systolic ejection murmur at the upper left sternal border.
- While VSDs can cause pulmonary overflow and a diastolic rumble, the **fixed splitting of S2** is characteristic of an ASD, not a VSD.
*Hypertrophic cardiomyopathy*
- HCM typically presents with a **harsh systolic murmur** that **increases with Valsalva maneuver** and decreases with squatting, reflecting dynamic outflow tract obstruction.
- It does not usually present with a mid-diastolic rumble or fixed splitting of S2.
*Rheumatic heart disease*
- Rheumatic heart disease often leads to **mitral stenosis**, which would present with a **loud S1** and an **opening snap** followed by a mid-diastolic rumble. Aortic involvement can also occur.
- While a mid-diastolic rumble is present, the absence of a history of rheumatic fever, a systolic ejection murmur at the pulmonic area, and fixed S2 splitting makes ASD more likely.
*Bicuspid aortic valve*
- A bicuspid aortic valve can cause an **early systolic ejection click** and a **systolic ejection murmur** at the **right upper sternal border** (aortic area) if stenosis is present.
- It does not typically cause a mid-diastolic rumble or fixed splitting of S2 unless severe aortic regurgitation or coexisting lesions are present, which are not suggested here.
Question 60: An 11-month-old boy is brought to the emergency department because of intermittent episodes of inconsolable crying for 4 hours. The parents report that the patient does not appear to be in discomfort between episodes, and moves and plays normally. The episodes have occurred at roughly 15-minute intervals and have each lasted a few minutes before subsiding. He has also vomited 3 times since these episodes began. The first vomitus appeared to contain food while the second and third appeared pale green in color. The patient was born at term and has been healthy. His immunizations are up-to-date. He has no history of recent travel. His older brother has Crohn's disease. The patient is at 50th percentile for height and 60th percentile for weight. He does not appear to be in acute distress. His temperature is 37.1°C (98.8°F), pulse is 125/min, respirations are 36/min, and blood pressure is 85/40 mm Hg. During the examination, the patient begins to cry and draws his knees up to his chest. Shortly thereafter, he passes stool with a mixture of blood and mucous; the patient's discomfort appears to resolve. Abdominal examination shows a sausage-shaped abdominal mass in the right upper quadrant. Which of the following is the most appropriate next step in the management of this patient?
A. MRI of the abdomen
B. Air enema
C. X-ray of the abdomen
D. Ultrasound of the abdomen (Correct Answer)
E. Stool cultures
F. Exploratory laparotomy
Explanation: ***Ultrasound of the abdomen***
- This patient presents with classic signs and symptoms of **intussusception**, including **intermittent colicky abdominal pain** (drawing knees to chest), **bilious vomiting**, **currant jelly stools** (blood and mucus), and a **sausage-shaped mass** in the right upper quadrant.
- **Ultrasound** is the **first-line diagnostic test** for suspected intussusception, showing the characteristic **target sign** (donut sign) on transverse view and **pseudokidney sign** on longitudinal view.
- While clinical findings are highly suggestive, **imaging confirmation is required** before attempting therapeutic reduction to rule out lead points or complications.
- After ultrasound confirms the diagnosis, **air or contrast enema** can be used for therapeutic reduction.
*Air enema*
- Air enema (pneumatic reduction) is an **appropriate therapeutic intervention** for intussusception, but it is typically performed **after ultrasound confirmation** of the diagnosis.
- It is both diagnostic and therapeutic, with success rates of 80-90% for uncomplicated cases.
- However, the question asks for the **most appropriate NEXT step**, which is imaging confirmation first.
*MRI of the abdomen*
- While MRI can visualize abdominal structures, it is **not the usual first-line diagnostic modality** for intussusception.
- It is **more time-consuming** and less readily available in an emergency setting compared to ultrasound.
- MRI would be unnecessary when ultrasound can rapidly confirm the diagnosis.
*X-ray of the abdomen*
- An **X-ray of the abdomen** can show signs of obstruction (e.g., dilated bowel loops, air-fluid levels, paucity of gas in right lower quadrant) but is **not sensitive or specific enough** to diagnose intussusception definitively.
- It does not offer therapeutic benefit, and **ultrasound** is the preferred initial imaging modality (sensitivity ~98-100%).
*Stool cultures*
- **Stool cultures** are used to identify bacterial or viral pathogens causing **gastroenteritis**, which would not explain the classic findings like a sausage-shaped mass or currant jelly stools.
- They would not be appropriate for managing acute abdominal obstruction with clear physical examination findings.
*Exploratory laparotomy*
- **Exploratory laparotomy** is a surgical procedure reserved for cases where **non-operative reduction fails**, there are signs of **perforation or peritonitis**, or there is **irreducible intussusception**.
- It is an **invasive procedure** and not the initial management step when the patient is hemodynamically stable without signs of perforation.
