Neuromuscular Disorders USMLE Step 1 Practice Question
A 17-year-old boy presents with severe muscle cramps and dark urine following intense basketball practice. Vital signs show BP 118/76, HR 102, RR 18, temp 37.2°C, SpO2 98%. Serum creatine kinase is 850 U/L with myoglobin detected in urine. He denies proximal weakness or family history of similar episodes. Symptoms resolve after brief rest, allowing him to resume activity at reduced intensity without recurrence. Which enzyme deficiency best explains this clinical presentation?
Answer choices
- AAcid maltase deficiency
- BHexosaminidase A deficiency
- CMuscle glycogen phosphorylase deficiencyCorrect answer
- DOrnithine transcarbamylase deficiency
- EGalactocerebrosidase deficiency
- FPhosphofructokinase deficiency (GSD type VII, Tarui disease)
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