Metabolism USMLE Step 1 Practice Question
A 7-year-old boy presents with declining school performance and progressive gait instability over 6 months. Vital signs show BP 108/65, HR 88, RR 20, temp 37°C, SpO2 98%. Examination reveals hyperpigmentation, lower extremity spasticity, and hyperreflexia; no fever noted. MRI demonstrates symmetric demyelination of parieto-occipital white matter. Plasma very-long-chain fatty acid levels are elevated. Accumulation of which substance most likely explains this leukodystrophy?
Answer choices
- AHomogentisic acid
- BVery long chain fatty acidsCorrect answer
- CGalactocerebroside
- DBranched chain amino acids
- EMethylmalonic acid
- FPhytanic acid (Refsum disease)
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