Metabolism USMLE Step 1 Practice Question
A 2-day-old female newborn presents with vomiting, tachypnea (RR 58/min), and progressive somnolence. Vital signs show HR 168/min, BP 65/40 mmHg, temperature 36.8°C, SpO2 98% on room air. Laboratory studies reveal plasma ammonia 480 μmol/L, blood urea nitrogen 8 mg/dL, and normal urinary orotic acid. Arterial blood gas demonstrates pH 7.48 with respiratory alkalosis. No hepatomegaly noted on examination. Which enzyme deficiency most likely explains these findings?
Answer choices
- AArgininosuccinate synthetase
- BCarbamoyl phosphate synthetase ICorrect answer
- COrnithine transcarbamylase
- DPyruvate carboxylase
- EFructose 1 phosphate aldolase
- FN-acetylglutamate synthase deficiency
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