Metabolism USMLE Step 1 Practice Question
A 2-week-old boy presents with poor feeding and lethargy. Vital signs show HR 145 bpm, RR 32/min, BP 68/42 mmHg, temperature 37.2°C. Laboratory studies reveal high anion gap metabolic acidosis (pH 7.21, HCO3 12 mEq/L), ketonemia, hyperammonemia (156 μmol/L), and elevated methylmalonic acid. Serum glucose is normal. He denies vomiting. Which of the following deficiencies best explains these findings?
Answer choices
- ADihydrofolate reductase deficiency
- BOrnithine transcarbamylase deficiency
- CBiotin deficiency only
- DVitamin B12 deficiency or methylmalonyl CoA mutase deficiencyCorrect answer
- EThiamine deficiency
- FPyruvate dehydrogenase deficiency
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