USMLE Step 1 Question of the Day
Test your knowledge with a hand-picked multiple-choice question.
A 3-year-old girl is evaluated for recurrent episodes of lethargy and rapid breathing during viral illnesses or after overnight fasting. She has no chronic medications and normal development; there is no hepatomegaly between episodes. During an episode, she is tachypneic but otherwise well-appearing. Labs: glucose 42 mg/dL (70–99), lactate 6.2 mmol/L (0.5–2.2), beta-hydroxybutyrate 4.0 mmol/L (0.0–0.4), bicarbonate 17 mEq/L (22–29), AST 38 U/L (10–40), ALT 29 U/L (7–56). Between episodes, labs normalize. Episodes are prevented with frequent feeding and avoidance of prolonged fasting.
Deficiency of which enzyme in gluconeogenesis most likely underlies this presentation?
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