USMLE Step 1 Question of the Day
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A 10-month-old girl presents after a generalized seizure following an overnight fast during a viral gastroenteritis. She was full-term with normal development. She takes no medications, and family history is unremarkable. On exam, she is lethargic without hepatomegaly. Labs: glucose 38 mg/dL (70–99), beta-hydroxybutyrate 0.1 mmol/L (0.0–0.4), ammonia 86 µmol/L (15–45), AST 58 U/L (10–40), ALT 44 U/L (7–56). Urinalysis shows increased dicarboxylic acids. After IV dextrose, mental status rapidly improves. Newborn screening previously suggested an abnormal acylcarnitine profile, but confirmatory testing was missed.
Deficiency of which enzyme best explains this patient's hypoketotic hypoglycemia?