Chromosomal disorders US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Chromosomal disorders. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Chromosomal disorders US Medical PG Question 1: A 16-year-old girl is brought to the physician because she has not yet had her 1st period. She was born at 39 weeks gestation via spontaneous vaginal delivery. She is up to date on all vaccines and meeting all developmental milestones. She has no history of a serious illness and takes no medications. Physical examination shows underdeveloped breasts with scant pubic and axillary hair. Speculum examination shows a short vagina and no cervix. The remainder of the physical examination shows no abnormalities. Pelvic ultrasound shows no uterus. Which of the following is the most likely karyotype in this patient?
- A. 47,XXY
- B. 45,X
- C. 46,XY (Correct Answer)
- D. 46,XX/46,XY
- E. 46,XX
Chromosomal disorders Explanation: ***46,XY***
- This karyotype describes an individual who is genetically male but presents phenotypically as female, often seen in **androgen insensitivity syndrome (AIS)**.
- The patient's underdeveloped breasts, scant pubic/axillary hair, short vagina with no cervix, and absent uterus (on ultrasound) are classic signs of AIS, where **testosterone is produced but tissues are unresponsive** due to receptor defects, leading to female external genitalia development and lack of Müllerian structures.
*47,XXY*
- This karyotype is associated with **Klinefelter syndrome**, which affects males and typically presents with tall stature, small testes, gynecomastia, and infertility.
- It does not explain the absence of a uterus or Mullerian structures, nor the specific presentation of underdeveloped secondary sexual characteristics in a phenotypic female.
*45,X*
- This karyotype describes **Turner syndrome**, which presents with primary amenorrhea, short stature, webbed neck, and **streak gonads** (absent or non-functional ovaries).
- While it causes primary amenorrhea and underdeveloped secondary sexual characteristics, Turner syndrome patients typically have a **uterus** (though small) and do not have an absent cervix or a short vagina in the way described.
*46,XX/46,XY*
- This represents **gonadal mosaicism**, where an individual has cell lines with both male and female karyotypes.
- The clinical presentation can be highly variable, ranging from ambiguous genitalia to female or male phenotypes, but it does not specifically account for the precise combination of primary amenorrhea, absent uterus, and underdeveloped secondary sexual characteristics as seen in AIS.
*46,XX*
- This is the normal female karyotype. While it can be associated with primary amenorrhea in conditions such as **Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome** (agenesis of the uterus and upper vagina), it would be accompanied by normal breast and pubic/axillary hair development due to functional ovaries.
- The patient's underdeveloped breasts and scant pubic/axillary hair suggest a problem with androgen action, not simply Müllerian agenesis in an otherwise hormonally normal female.
Chromosomal disorders US Medical PG Question 2: A 5-year-old boy is brought to the physician because of behavioral problems. His mother says that he has frequent angry outbursts and gets into fights with his classmates. He constantly complains of feeling hungry, even after eating a full meal. He has no siblings, and both of his parents are healthy. He is at the 25th percentile for height and is above the 95th percentile for weight. Physical examination shows central obesity, undescended testes, almond-shaped eyes, and a thin upper lip. Which of the following genetic changes is most likely associated with this patient's condition?
- A. Mitotic nondisjunction of chromosome 21
- B. Mutation of FBN-1 gene on chromosome 15
- C. Microdeletion of long arm of chromosome 7
- D. Loss of paternal gene expression on chromosome 15 (Correct Answer)
- E. Deletion of Phe508 on chromosome 7
Chromosomal disorders Explanation: ***Loss of paternal gene expression on chromosome 15***
- The patient's symptoms, including **hyperphagia**, **obesity**, behavioral issues, short stature, and **hypogonadism** (undescended testes), are characteristic of **Prader-Willi syndrome**.
- Prader-Willi syndrome is most commonly caused by the **loss of paternal gene expression** from the **q11-q13 region of chromosome 15**, either due to a paternal deletion, maternal uniparental disomy, or a defect in the imprinting center.
*Microdeletion of long arm of chromosome 7*
- A microdeletion on the long arm of chromosome 7 (7q11.23) is associated with **Williams syndrome**, characterized by an **elfin facial appearance**, supravalvular aortic stenosis, and intellectual disability.
- This does not match the patient's symptoms of obesity, hyperphagia, or hypogonadism.
*Deletion of Phe508 on chromosome 7*
- A deletion of phenylalanine at position 508 (**ΔF508**) on chromosome 7 is the most common mutation in the **cystic fibrosis transmembrane conductance regulator (CFTR)** gene, causing **cystic fibrosis**.
- Cystic fibrosis is an **autosomal recessive disorder** requiring mutations in both alleles (inherited from both parents), and primarily affects the exocrine glands, leading to lung disease, pancreatic insufficiency, and infertility, which are unrelated to the patient's presentation.
*Mutation of FBN-1 gene on chromosome 15*
- A mutation in the **FBN1 gene** on chromosome 15 (15q21.1) causes **Marfan syndrome**, which is a connective tissue disorder.
- Marfan syndrome presents with tall stature, long limbs (**arachnodactyly**), lens dislocation, and aortic root dilation, none of which are described in this patient.
*Mitotic nondisjunction of chromosome 21*
- Mitotic nondisjunction of chromosome 21 can lead to **mosaic Down syndrome**, but **trisomy 21** (due to meiotic nondisjunction) is the most common cause of Down syndrome.
- Down syndrome is associated with characteristic facial features, intellectual disability, and congenital heart defects, which are distinct from the symptoms presented.
Chromosomal disorders US Medical PG Question 3: A 19-year-old male from rural West Virginia presents to his family medicine doctor to discuss why he is having trouble getting his wife pregnant. On exam, he is 6 feet 2 inches with a frail frame and broad hips for a male his size. He is noted to have mild gynecomastia, no facial hair, and small, underdeveloped testes. He claims that although he has a lower libido than most of his friends, he does have unprotected sex with his wife. His past medical history is notable for developmental delay and difficulties in school. What is the most likely chromosomal abnormality in this patient?
- A. Trisomy 13
- B. 45: XO
- C. Trisomy 21
- D. 47: XYY
- E. 47: XXY (Correct Answer)
Chromosomal disorders Explanation: ***47: XXY***
- The patient's presentation with **infertility**, small testes, **gynecomastia**, eunuchoid body habitus (tall, frail frame, broad hips), lack of facial hair, and **developmental delay** are classic features of **Klinefelter syndrome (47, XXY)**.
- This chromosomal abnormality leads to primary **hypogonadism** due to the presence of an extra X chromosome in males.
*Trisomy 13*
- Trisomy 13, or **Patau syndrome**, is characterized by severe developmental anomalies, including **cleft lip and palate**, polydactyly, and severe neurological defects.
- Infants with Trisomy 13 rarely survive beyond the first year and do not present with the described signs of hypogonadism or gynecomastia in adolescence.
*45: XO*
- **45, XO** or **Turner syndrome** affects females and is characterized by **short stature**, primary amenorrhea, webbed neck, and **gonadal dysgenesis (streak gonads)**.
- This karyotype is incompatible with a male phenotype and the symptoms described.
*Trisomy 21*
- Trisomy 21, or **Down syndrome**, is associated with distinct facial features, intellectual disability, and congenital heart defects.
- While individuals with Down syndrome may have fertility issues, they do not typically present with the specific combination of **gynecomastia**, eunuchoid habitus, and **small testes** seen in this patient.
*47: XYY*
- **47, XYY syndrome** is associated with increased height and potentially some learning difficulties, but typically does not cause the significant **hypogonadism**, **gynecomastia**, or **small testes** seen in this patient.
- Men with 47, XYY usually have normal sexual development and fertility, though some may experience learning disabilities or behavioral problems.
Chromosomal disorders US Medical PG Question 4: A 36-year-old G4P0A3 woman presents at the prenatal diagnostic center at 18 weeks of gestation for the scheduled fetal anomaly scan. The patient's past medical history reveals spontaneous abortions. She reports that her 1st, 2nd, and 3rd pregnancy losses occurred at 8, 10, and 12 weeks of gestation, respectively. Ultrasonography indicates a female fetus with cystic hygroma (measuring 4 cm x 5 cm in size) and fetal hydrops. Which of the following karyotypes does her fetus most likely carry?
- A. 45 X0 (Correct Answer)
- B. Monosomy 18
- C. Trisomy 13
- D. Trisomy 21
- E. Monosomy 13
Chromosomal disorders Explanation: ***45 X0***
- The presence of **cystic hygroma** and **fetal hydrops** strongly suggests **Turner syndrome (45, X0)**, as these are classic sonographic findings.
- The history of **recurrent early pregnancy losses** is also consistent with chromosomal aneuploidies, with 45, X0 being a common cause of such losses.
*Monosomy 18*
- **Monosomy 18** is a very rare and usually lethal chromosomal abnormality, typically resulting in **early miscarriage**.
- Its clinical presentation, if live-born, is distinct and does not primarily feature **cystic hygroma** or **hydrops** as the main diagnostic clues.
*Trisomy 13*
- **Trisomy 13 (Patau syndrome)** is associated with severe malformations, including **cleft lip/palate**, **polydactyly**, and **holoprosencephaly**.
- While it can cause fetal hydrops and other structural anomalies, **cystic hygroma** is not its most characteristic or common sonographic marker in the way it is for Turner syndrome.
*Trisomy 21*
- **Trisomy 21 (Down syndrome)** is characterized by **nuchal translucency** and **cardiac defects**, but **cystic hygroma** and **hydrops** are less common and less severe than in Turner syndrome.
- The constellation of findings in this case points more strongly to Turner syndrome.
*Monosomy 13*
- **Monosomy 13** is an extremely rare and usually **lethal** chromosomal anomaly, often leading to early spontaneous abortion.
- It would typically result in more severe generalized developmental defects rather than the specific combination of **cystic hygroma** and **hydrops** seen here.
Chromosomal disorders US Medical PG Question 5: A 1-week-old baby is brought to the pediatrician’s office for a routine checkup. On examination, she is observed to have microcephaly with a prominent occiput. She also has clenched fists and rocker-bottom feet with prominent calcanei. A cardiac murmur is evident on auscultation. Based on the clinical findings, a diagnosis of nondisjunction of chromosome 18 is suspected. The pediatrician orders a karyotype for confirmation. He goes on to explain to the mother that her child will face severe growth difficulties. Even if her daughter progresses beyond a few months, she will not be able to reach developmental milestones at the appropriate age. In addition to the above, which of the following is most likely a consequence of this genetic disturbance?
- A. Supravalvular aortic stenosis
- B. Alzheimer’s disease
- C. Macroglossia
- D. Cutis aplasia
- E. Death within the first year of life (Correct Answer)
Chromosomal disorders Explanation: ***Death within the first year of life***
- This patient has Trisomy 18, also known as Edwards syndrome, which is characterized by a high mortality rate, with **90-95% of affected infants dying within the first year** due to severe congenital anomalies, especially cardiac defects.
- **Rocker-bottom feet**, **clenched fists with overlapping fingers**, **microcephaly with a prominent occiput**, and **congenital heart defects** (such as ventricular septal defects or patent ductus arteriosus) are classic features of Trisomy 18.
*Cutis aplasia*
- **Cutis aplasia** (a congenital absence of skin) is a characteristic symptom of **Trisomy 13 (Patau syndrome)**, not Trisomy 18.
- While both are chromosomal abnormalities, their specific phenotypic presentations differ, making cutis aplasia less likely in this case.
*Macroglossia*
- **Macroglossia** (an enlarged tongue) is a common feature of **Down syndrome (Trisomy 21)**.
- It is not typically associated with Trisomy 18, which presents with distinct facial and oral features.
*Alzheimer’s disease*
- Individuals with **Down syndrome (Trisomy 21)** have an increased risk of developing **early-onset Alzheimer's disease**, often by middle age.
- This is due to the triplication of the **APP gene**, located on chromosome 21, which is involved in amyloid-beta plaque formation.
*Supravalvular aortic stenosis*
- **Supravalvular aortic stenosis** (narrowing of the aorta above the aortic valve) is a characteristic cardiac finding in **Williams syndrome**, a microdeletion syndrome involving chromosome 7.
- Williams syndrome is also associated with elfin facies, intellectual disability, and a friendly personality, none of which align with this patient's presentation.
Chromosomal disorders US Medical PG Question 6: A 9-year-old boy is brought to the physician because his parents are concerned that he has been unable to keep up with his classmates at school. He is at the 4th percentile for height and at the 15th percentile for weight. Physical examination shows dysmorphic facial features. Psychologic testing shows impaired intellectual and adaptive functions. Genetic analysis shows a deletion of the long arm of chromosome 7. Which of the following is the most likely additional finding in this patient?
- A. Absent thymus gland
- B. Supravalvular aortic stenosis (Correct Answer)
- C. Brushfield spots on the iris
- D. Testicular enlargement
- E. Hand flapping movements
Chromosomal disorders Explanation: ***Supravalvular aortic stenosis***
- The clinical presentation, including **dysmorphic facial features**, **growth restriction**, and **intellectual disability**, coupled with a **deletion on the long arm of chromosome 7**, is highly suggestive of **Williams syndrome**.
- **Supravalvular aortic stenosis** is a classic cardiovascular finding in **Williams syndrome**, present in about 75% of affected individuals.
*Absent thymus gland*
- An absent thymus gland is characteristic of **DiGeorge syndrome**, which is caused by a **deletion on chromosome 22q11**.
- This patient's genetic analysis indicates a deletion on **chromosome 7**, not chromosome 22.
*Brushfield spots on the iris*
- **Brushfield spots** are characteristic of **Down syndrome** (**trisomy 21**).
- The genetic finding of a **deletion on chromosome 7** rules out Down syndrome as the underlying cause.
*Testicular enlargement*
- **Testicular enlargement** is a hallmark feature of **Fragile X syndrome**, a genetic condition caused by an **FMR1 gene mutation** on the X chromosome.
- This patient's symptoms and genetic findings of a **chromosome 7 deletion** are not consistent with Fragile X syndrome.
*Hand flapping movements*
- **Hand flapping** is a common repetitive behavior observed in individuals with **autism spectrum disorder** and is also seen in some other genetic conditions like **Rett syndrome**.
- While individuals with Williams syndrome may have unique behavioral profiles, hand flapping is not a specific or typical feature of the syndrome, and the genetic finding points to Williams syndrome.
Chromosomal disorders US Medical PG Question 7: A 6-year-old male presents to the pediatrician with seizures. His mother reports that the patient has had two seizures lasting about 30 seconds each over the last three days. She reports that the patient has previously had seizures a few times per year since he was 12 months of age. The patient’s past medical history is otherwise notable for intellectual disability. He rolled over at 14 months of age and walked at 24 months of age. The patient’s mother denies any family history of epilepsy or other neurologic diseases. The patient is in the 3rd percentile for height and the 15th percentile for weight. On physical exam, he has a happy demeanor with frequent smiling. The patient has strabismus and an ataxic gait accompanied by flapping of the hands. He responds intermittently to questions with one-word answers. This patient is most likely to have which of the following genetic abnormalities?
- A. Chromosomal macrodeletion on chromosome 5
- B. Maternal uniparental disomy of chromosome 15
- C. Imprinting defect on chromosome 11
- D. Trinucleotide repeat disorder
- E. Paternal uniparental disomy of chromosome 15 (Correct Answer)
Chromosomal disorders Explanation: ***Paternal uniparental disomy of chromosome 15***
- The patient's presentation with **intellectual disability**, **seizures**, developmental delay (rolling over at 14 months, walking at 24 months), **ataxic gait**, **happy demeanor** with frequent smiling, and hand flapping are classic features of **Angelman syndrome**.
- **Angelman syndrome** requires loss of function of the maternal UBE3A gene on chromosome 15, which is paternally imprinted (meaning only the maternal copy is active).
- **Paternal uniparental disomy** means both copies of chromosome 15 come from the father, resulting in no functional maternal UBE3A gene, causing Angelman syndrome.
- Other causes include maternal deletion of 15q11-q13 (most common), imprinting defects, and UBE3A mutations.
*Maternal uniparental disomy of chromosome 15*
- This causes **Prader-Willi syndrome**, not Angelman syndrome.
- When both chromosome 15s come from the mother, there is no paternal contribution, and paternally expressed genes are lost.
- Prader-Willi presents with **neonatal hypotonia**, **feeding difficulties**, later **hyperphagia** and **obesity**, which are not seen in this patient.
*Imprinting defect on chromosome 11*
- This is associated with **Beckwith-Wiedemann syndrome**, which presents with **macroglossia**, **omphalocele**, **hemihyperplasia**, and increased tumor risk.
- The clinical presentation is distinctly different from this patient's features.
*Trinucleotide repeat disorder*
- Includes conditions such as **Fragile X syndrome**, **Huntington's disease**, and **Myotonic dystrophy**.
- Fragile X syndrome can cause intellectual disability and seizures but typically presents with **macroorchidism** (in post-pubertal males), long face, large ears, and **autistic features** rather than the happy demeanor seen here.
*Chromosomal macrodeletion on chromosome 5*
- This is characteristic of **Cri du Chat syndrome** (5p deletion).
- Presents with a distinctive **cat-like cry**, **microcephaly**, widely spaced eyes, and severe intellectual disability, which do not match this patient's presentation.
Chromosomal disorders US Medical PG Question 8: 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)
Chromosomal disorders 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.
Chromosomal disorders US Medical PG Question 9: A 15-year-old boy is brought to the physician by his mother for a well-child examination. He recently stopped attending his swim classes. The patient is at the 97th percentile for height and the 50th percentile for weight. Examination shows decreased facial hair, bilateral breast enlargement, and long extremities. Genital examination shows scant pubic hair, small testes, and a normal-sized penis. Further evaluation is most likely to show which of the following karyotypes?
- A. 45,XO/46,XX
- B. 45,XO
- C. 47,XYY
- D. 46,XX/46,XY
- E. 47,XXY (Correct Answer)
Chromosomal disorders Explanation: ***47,XXY***
- The patient's presentation with **tall stature**, **gynecomastia**, **small testes**, and **scant pubic hair** is characteristic of **Klinefelter syndrome**, which is caused by a **47,XXY karyotype**.
- **Hypogonadism** in Klinefelter syndrome leads to **decreased testosterone production**, explaining the lack of facial hair and undeveloped secondary sexual characteristics.
*45,XO/46,XX*
- This mosaic karyotype is associated with **Turner syndrome**, which primarily affects females and presents with features like **short stature**, **gonadal dysgenesis**, and **webbed neck**.
- Males with this karyotype are rare and would not exhibit the typical features described, such as **gynecomastia** and eunuchoid body habitus.
*45,XO*
- This is the classic karyotype for **Turner syndrome**, which is exclusively found in phenotypic females.
- Individuals with 45,XO present with **short stature**, **streak gonads**, and a lack of secondary sexual characteristics, none of which align with the male patient's symptoms.
*47,XYY*
- Individuals with **XYY syndrome** (Jacob syndrome) are typically **tall** but usually have **normal sexual development** and **fertility**.
- This karyotype does not explain the **gynecomastia**, **small testes**, or **decreased facial hair** seen in the patient.
*46,XX/46,XY*
- This karyotype indicates **gonadal mosaicism**, also known as **ovotesticular disorder of sex development (DSD)** or **chimerism**, where an individual has both ovarian and testicular tissue.
- While it can present with ambiguous genitalia and mixed secondary sexual characteristics, the specific constellation of **tall stature**, **gynecomastia**, and **small testes** is more indicative of Klinefelter syndrome.
Chromosomal disorders US Medical PG Question 10: A newborn male is evaluated in the hospital nursery two hours after birth. The patient was born at 39 weeks of gestation to a 30-year-old primigravid via vaginal delivery. The patient’s mother received routine prenatal care, and the pregnancy was uncomplicated. The patient’s anatomy ultrasound at 20 weeks of gestation was unremarkable. The patient’s mother denies any family history of genetic diseases. The patient’s Apgar scores were notable for poor muscle tone at both one and five minutes of life. The patient’s birth weight is 2.6 kg (5 lb 11 oz), which is at the 5th percentile. His height and head circumference are in the 15th and 3rd percentile, respectively. On physical exam, the patient has a wide nasal bridge, downslanting palpebral fissures, and widely spaced eyes. He has good respiratory effort with a high-pitched cry. This patient is most likely to have experienced a deletion on which of the following chromosomes?
- A. 4p
- B. 5q
- C. 7q
- D. 15q
- E. 5p (Correct Answer)
Chromosomal disorders Explanation: ***5p***
- The constellation of findings, including **low birth weight**, **microcephaly**, **hypotonia**, **widely spaced eyes**, **downslanting palpebral fissures**, **wide nasal bridge**, and a **high-pitched cry**, is highly characteristic of **Cri-du-chat syndrome**.
- **Cri-du-chat syndrome** is caused by a **deletion of the short arm of chromosome 5 (5p)**.
*4p*
- A deletion on **4p** is associated with **Wolf-Hirschhorn syndrome**, which presents with **microcephaly**, a distinct **"Greek helmet" facial appearance**, and often severe intellectual disability, which are not perfectly aligned with all features described.
- While there can be overlapping features like growth restriction and developmental delay, the specific craniofacial features and the characteristic cry of Cri-du-chat are not typical for Wolf-Hirschhorn syndrome.
*5q*
- A deletion on **5q** is associated with various conditions, including some forms of **myelodysplastic syndromes** (particularly 5q- syndrome), which are hematologic disorders and not typically presenting with the described birth defects.
- While deletions can occur on the long arm of chromosome 5, they do not cause Cri-du-chat syndrome; that is specifically a 5p deletion.
*7q*
- Deletions on **7q** are associated with conditions like **Williams syndrome** (a microdeletion on 7q11.23, characterized by "elfin" facies, supravalvular aortic stenosis, and unique personality traits) or **Silver-Russell syndrome** (associated with some 7q deletions, causing growth restriction and characteristic facial features).
- The described presentation does not match the typical features of conditions linked to 7q deletions.
*15q*
- Deletions on **15q** are linked to conditions such as **Prader-Willi syndrome** (paternal deletion of 15q11-q13, causing hypotonia, feeding difficulties in infancy followed by hyperphagia, and intellectual disability) and **Angelman syndrome** (maternal deletion or mutation on 15q11-q13, presenting with severe intellectual disability, ataxia, and inappropriate laughter).
- The clinical features presented do not align with the characteristic presentation of either Prader-Willi or Angelman syndrome.
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