A 4-year-old boy has progressive spastic diplegia, intellectual decline, and recurrent vomiting. Plasma ammonia is mildly elevated at 110 micromol/L, and plasma arginine is markedly increased. Urinary orotic acid is normal. The most likely diagnosis is:
- A Ornithine transcarbamylase deficiency
- B Arginase deficiency (argininemia) ✓
- C Citrullinemia type I
- D Argininosuccinate lyase deficiency
Correct answer: B. Arginase deficiency (argininemia)
Explanation
Arginase, the last urea cycle enzyme, hydrolyzes arginine to urea and ornithine. Its deficiency causes chronic rather than neonatal hyperammonemia, with the distinctive feature of progressive spasticity, plus elevated plasma arginine. OTC deficiency gives high orotic acid and low citrulline, killing option A. Citrullinemia and argininosuccinate lyase deficiency present with marked elevations of citrulline and argininosuccinate respectively, not isolated hyperargininemia, so options C and D fail the amino acid profile.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.