USMLE Step 1 Question of the Day
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A 9-month-old boy has recurrent vomiting and lethargy shortly after the introduction of fruit purees and juices. He was previously healthy; family history is negative. On exam, he is irritable with palpable hepatomegaly. Labs: glucose 48 mg/dL (70–99), phosphate 2.0 mg/dL (2.5–4.5), AST 132 U/L (10–40), ALT 118 U/L (7–56), bicarbonate 19 mEq/L (22–29). Urinalysis is positive for reducing substances. Symptoms improve with IV dextrose and strict avoidance of dietary fructose and sucrose.
Deficiency of which enzyme best explains this patient's presentation?
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