Metabolism USMLE Step 1 Practice Question
A 3 day old male newborn develops progressive lethargy, poor feeding, and tachypnea. He becomes difficult to arouse but has no hepatomegaly. Laboratory studies show markedly elevated ammonia, low blood urea nitrogen, respiratory alkalosis, and increased urinary orotic acid. Which of the following enzyme deficiencies is the most likely cause?
Answer choices
- ACarbamoyl phosphate synthetase I
- BMethylmalonyl CoA mutase
- COrnithine transcarbamylaseCorrect answer
- DArginase
- EArgininosuccinate lyase
- FN-acetylglutamate synthase
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.