Neurodegenerative Diseases USMLE Step 1 Practice Question
A 16-year-old boy presents with slowly progressive proximal muscle weakness over 3 years but remains ambulatory and plays modified sports. His maternal uncle had a similar disorder and survived into adulthood. Vital signs are normal (BP 120/78, HR 88, RR 16, Temp 37°C). Serum creatine kinase is elevated at 2,200 IU/L. Cardiac evaluation shows no involvement. Which of the following mutations is most likely present?
Answer choices
- AMitochondrial DNA deletion impairing oxidative phosphorylation
- BIn frame mutation in the dystrophin gene allowing partially functional proteinCorrect answer
- CNonsense mutation in the SMN1 gene
- DPaternal CAG repeat expansion in the androgen receptor gene
- EPostsynaptic acetylcholine receptor mutation
- FOut of frame mutation in the dystrophin gene resulting in premature stop codon
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