Neuromuscular Disorders USMLE Step 1 Practice Question
A 6-month-old boy presents with developmental delay and inability to sit unsupported. Vital signs show HR 110 bpm, RR 28, temp 37°C, SpO2 98%. On exam, he has marked hypotonia, tongue fasciculations, and absent deep tendon reflexes. CK level is elevated at 800 U/L. He denies respiratory distress. Family history is unremarkable. Which of the following genetic abnormalities is most likely present?
Answer choices
- AMutation in PMP22
- BTrinucleotide repeat expansion in HTT
- CDeletion of dystrophin on X chromosome
- DMutation in GAA
- EDeletion of SMN1 geneCorrect answer
- FMutation in LMNA
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