Genetic disorders US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Genetic disorders. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Genetic disorders US Medical PG Question 1: A 25-year-old man with a genetic disorder presents for genetic counseling because he is concerned about the risk that any children he has will have the same disease as himself. Specifically, since childhood he has had difficulty breathing requiring bronchodilators, inhaled corticosteroids, and chest physiotherapy. He has also had diarrhea and malabsorption requiring enzyme replacement therapy. If his wife comes from a population where 1 in 10,000 people are affected by this same disorder, which of the following best represents the likelihood a child would be affected as well?
- A. 0.01%
- B. 2%
- C. 0.5%
- D. 1% (Correct Answer)
- E. 50%
Genetic disorders Explanation: ***Correct Option: 1%***
- The patient's symptoms (difficulty breathing requiring bronchodilators, inhaled corticosteroids, and chest physiotherapy; diarrhea and malabsorption requiring enzyme replacement therapy) are classic for **cystic fibrosis (CF)**, an **autosomal recessive disorder**.
- For an autosomal recessive disorder with a prevalence of 1 in 10,000 in the general population, **q² = 1/10,000**, so **q = 1/100 = 0.01**. The carrier frequency **(2pq)** is approximately **2q = 2 × (1/100) = 1/50 = 0.02**.
- The affected man is **homozygous recessive (aa)** and will always pass on the recessive allele. His wife has a **1/50 chance of being a carrier (Aa)**. If she is a carrier, she has a **1/2 chance of passing on the recessive allele**.
- Therefore, the probability of an affected child = **(Probability wife is a carrier) × (Probability wife passes recessive allele) = 1/50 × 1/2 = 1/100 = 1%**.
*Incorrect Option: 0.01%*
- This percentage is too low and does not correctly account for the carrier frequency in the population and the probability of transmission from a carrier mother.
*Incorrect Option: 2%*
- This represents approximately the carrier frequency (1/50 ≈ 2%), but does not account for the additional 1/2 probability that a carrier mother would pass on the recessive allele.
*Incorrect Option: 0.5%*
- This value would be correct if the carrier frequency were 1/100 instead of 1/50, which does not match the given population prevalence.
*Incorrect Option: 50%*
- **50%** would be the risk if both parents were carriers of an autosomal recessive disorder (1/4 chance = 25% for affected, but if we know one parent passes the allele, conditional probability changes). More accurately, 50% would apply if the disorder were **autosomal dominant** with one affected parent, which is not the case here.
Genetic disorders US Medical PG Question 2: A 23-year-old woman and her husband come to a genetic counselor because she is concerned about the chance of having an inherited defect if they had a child. Family history reveals no significant family history in her husband; however, her sister had a son who has seizures, failure to thrive, and neurodegeneration. She does not remember the name of the disease but remembers that her nephew had sparse, brittle hair that kinked in odd directions. She does not think that any other members of her family including her sister's husband have had this disorder. If this couple had a son, what is the most likely chance that he would have the same disorder that affected the patient's nephew?
- A. 100%
- B. 12.5%
- C. 25% (Correct Answer)
- D. 50%
- E. Close to 0%
Genetic disorders Explanation: ***25%***
- The nephew's symptoms of **seizures, failure to thrive, neurodegeneration**, and **sparse, brittle, kinky hair** are highly indicative of **Menkes disease**, an **X-linked recessive** disorder.
- Since the patient's sister had an affected son, the sister is an **obligate carrier** of the mutation.
- The patient and her sister share the same parents, so their mother must be a carrier (or have the mutation).
- The patient herself has a **50% chance of being a carrier**.
- **If the patient is a carrier**, each son has a **50% chance** of being affected.
- **Overall probability**: 0.5 (chance patient is carrier) × 0.5 (chance son inherits mutation) = **0.25 = 25%**.
*Close to 0%*
- This would only be correct if the patient had no chance of being a carrier, which is not the case given her family history.
- Her sister's affected son confirms the mutation is present in the maternal lineage.
*100%*
- This would only occur if the patient were definitely a carrier AND all male offspring inherited the mutation, or if the disorder were autosomal dominant with complete penetrance.
- For **X-linked recessive** disorders, even carrier mothers only pass the mutation to 50% of sons on average.
*12.5%*
- This percentage might represent additional generational steps or compound probabilities not relevant to this direct parent-child scenario.
- The correct calculation for this scenario is 50% × 50% = 25%.
*50%*
- This would be correct if we knew with certainty that the patient is a carrier.
- However, since we only know her sister is a carrier, the patient has a 50% chance of being a carrier herself, making the overall risk 25%.
- This is a common error in genetic counseling calculations—forgetting to account for the uncertain carrier status of the at-risk individual.
Genetic disorders US Medical PG Question 3: A 30-year-old man is brought into the emergency room for complaints of acute onset chest pain and shortness of breath. He has a history of mental retardation and lives at home with his adoptive parents. His parents inform you that he has not seen a doctor since he was adopted as child and that he currently takes no medications. The patient's temperature is 99.1°F (37.3°C), pulse is 108/min, blood pressure is 125/70 mmHg, respirations are 25/min, and oxygen saturation is 92% on 2L nasal cannula. Physical exam is notable for a tall, thin individual with high-arched feet and mild pectus excavatum. There is mild asymmetry in the lower extremities with discomfort to dorsiflexion of the larger leg. Lung auscultation reveals no abnormalities. What is the most appropriate next step in management?
- A. Chest radiograph
- B. Serum blood test
- C. Genetic testing
- D. Angiogram
- E. Electrocardiogram (Correct Answer)
Genetic disorders Explanation: ***Correct: Electrocardiogram***
- **Acute chest pain** mandates an immediate **ECG** as the first diagnostic test to rule out **ST-elevation myocardial infarction (STEMI)**, which requires emergent intervention (PCI or thrombolysis).
- While this patient's presentation is highly suspicious for **pulmonary embolism (PE)** given the **unilateral leg swelling with pain on dorsiflexion** (suggestive of DVT), **tachycardia**, **tachypnea**, and **hypoxemia**, the ECG remains the most appropriate initial step per ACLS protocols for chest pain.
- ECG can also show findings suggestive of PE (sinus tachycardia, S1Q3T3 pattern, right heart strain) and help differentiate cardiac from pulmonary etiologies.
- The **Marfanoid features** (tall, thin, pectus excavatum, high-arched feet) raise concern for **aortic dissection**, which ECG can help evaluate alongside clinical assessment.
*Incorrect: Chest radiograph*
- Chest X-ray is critical in the workup and would typically be ordered simultaneously with or immediately after ECG in this patient with suspected PE.
- CXR helps exclude pneumothorax, pneumonia, and can show classic PE findings (Westermark sign, Hampton's hump), though it is often normal in PE.
- In the context of Marfan syndrome, CXR can reveal a widened mediastinum suggesting aortic dissection.
- However, ECG takes precedence as the immediate first step for any acute chest pain presentation.
*Incorrect: Serum blood test*
- Laboratory tests including **cardiac troponins** (for MI), **D-dimer** (for PE), and **CBC** are important but take time to result.
- D-dimer would be useful in this moderate-to-high probability PE case, but imaging (CT pulmonary angiography) would be more appropriate given the high clinical suspicion.
- Blood tests do not provide the immediate actionable information needed as the first diagnostic step in acute chest pain.
*Incorrect: Genetic testing*
- While the patient's phenotype suggests **Marfan syndrome** or another connective tissue disorder, genetic testing is an outpatient diagnostic tool for long-term management.
- It provides no immediate utility in the acute management of chest pain and respiratory distress.
- Genetic counseling and testing would be appropriate after stabilization and initial workup.
*Incorrect: Angiogram*
- **CT pulmonary angiography** would be the definitive test for PE diagnosis after initial ECG and CXR, but is not the immediate first step.
- **Cardiac catheterization** would be indicated if ECG showed STEMI or if there was high suspicion for ACS after initial workup.
- **CT aortography** might be needed if aortic dissection is suspected based on initial findings.
- Angiography is an invasive or advanced imaging procedure performed after non-invasive screening tests guide the diagnosis.
Genetic disorders US Medical PG Question 4: A 3-year-old is brought to the pediatrician by his mother because she is concerned about recent changes to his behavior. She states that he has seemed to regress in his motor development and has been having occasional brief episodes of uncontrollable shaking. During the subsequent work up, a muscle biopsy is obtained which demonstrates red ragged fibers and a presumptive diagnosis of a genetic disease made. The mother asks if her other son will be affected. What should be the physician's response?
- A. There is a 50% chance he will be affected
- B. There is a 100% chance he will be affected, and the severity will be the same
- C. There is a 25% chance he will be affected
- D. There is a 100% chance he will be affected, but the severity may be different (Correct Answer)
- E. He will be unaffected
Genetic disorders Explanation: ***There is a 100% chance he will be affected, but the severity may be different***
- The patient's symptoms (motor regression, seizures, red ragged fibers on muscle biopsy) are classic for a **mitochondrial disorder**, which are inherited via **maternal inheritance**.
- All children of an affected mother will inherit the affected mitochondria; however, the **heteroplasmy** (proportion of mutated mitochondria inherited) can vary, leading to different disease severities.
*There is a 50% chance he will be affected*
- This inheritance pattern is typical for **autosomal dominant** disorders, or occasionally X-linked disorders in males.
- Mitochondrial disorders do not follow autosomal dominant inheritance, as they are exclusively inherited from the mother.
*There is a 100% chance he will be affected, and the severity will be the same*
- While there is a 100% chance of inheriting the mutated mitochondria from an affected mother, the **phenotypic expression and severity can vary widely** due to heteroplasmy.
- The proportion of mutated mitochondria can differ in various tissues and between offspring, leading to variable clinical manifestations.
*There is a 25% chance he will be affected*
- This represents the risk of inheritance for an **autosomal recessive** disorder when both parents are carriers.
- Mitochondrial inheritance does not follow an autosomal recessive pattern.
*He will be unaffected*
- This would only be true if the mother's mitochondrial DNA were not affected or if the inheritance pattern allowed for some children to be completely spared, which is not the case for mitochondrial disorders.
- Since the mother is the carrier of the mitochondrial mutation, all her children will inherit the mutated mitochondria.
Genetic disorders US Medical PG Question 5: 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
Genetic 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.
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