A 34-year-old man has recurrent nocturnal confusion and episodes of lethargy. He spontaneously prefers protein-rich foods and avoids carbohydrates. Workup shows moderate hyperammonemia, elevated plasma citrulline, arginine, and lysine, and a high threonine to serine ratio. The underlying defect involves:
- A Deficiency of the aspartate-glutamate carrier citrin encoded by SLC25A13 ✓
- B Argininosuccinate synthetase gene mutation
- C Ornithine transcarbamylase gene mutation on the X chromosome
- D Carbamoyl phosphate synthetase-I promoter deletion
Correct answer: A. Deficiency of the aspartate-glutamate carrier citrin encoded by SLC25A13
Explanation
Adult-onset type II citrullinemia results from citrin deficiency, an autosomal recessive loss of the mitochondrial aspartate-glutamate carrier. Impaired aspartate export limits the second nitrogen source of the urea cycle, raising citrulline, arginine, and lysine. The self-imposed protein preference and carbohydrate aversion are characteristic clues. Option B describes citrullinemia type I, which presents in neonates rather than adults with this dietary pattern.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.