Metabolism USMLE Step 1 Practice Question
A 17-year-old male presents with acute left flank pain and gross hematuria. Vital signs show BP 128/82 mmHg, HR 92 bpm, RR 16, temp 37.2°C, SpO2 98%. Urinalysis reveals hexagonal crystals and 3+ blood. Serum creatinine is 0.9 mg/dL. He denies fever and reports recurrent kidney stones since age 8 with no prior UTIs. Urine pH is 5.2. Which metabolic pathway defect most likely explains his presentation?
Answer choices
- ACystathionine beta synthase deficiency
- BDeficiency of homogentisate oxidase
- CDefect in uric acid transporter URAT1
- DRenal proximal tubular transporter defect for cystine, ornithine, lysine, and arginineCorrect answer
- EDeficiency of xanthine oxidase
- FPrimary hyperoxaluria from glyoxylate aminotransferase deficiency causing calcium oxalate nephrolithiasis
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