Metabolism USMLE Step 1 Practice Question
A 6-day-old male newborn presents with poor feeding, vomiting, and alternating hypotonia and hypertonia with intermittent opisthotonos. Vital signs reveal HR 148/min, RR 32/min, and temperature 37.2Ā°C. His urine has a characteristic sweet odor. Laboratory studies demonstrate elevated plasma branched-chain amino acids (leucine 850 Ī¼mol/L; normal <200), elevated urine branched-chain Ī±-ketoacids, and normal glucose. He denies seizure activity. Which enzyme deficiency is most likely responsible?
Answer choices
- AOrnithine transcarbamylase
- BPhenylalanine hydroxylase
- CTyrosinase
- DHomogentisate oxidase
- EBranched chain alpha ketoacid dehydrogenaseCorrect answer
- FMaple syrup urine disease branching enzyme
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