Summary

Carbamoyl phosphate synthetase 1 (CPS1; MIM *608307; E.C. 6.3.4.16) is the first rate-limiting enzyme of the urea cycle, an essential metabolic pathway for ammonia detoxification. CPS1 deficiency (CPS1-D) is characterized by severe hyperammonemia during disease exacerbations. During a metabolic crisis, children with CPS1-D are admitted with vomiting, altered mental status, and high serum levels of ammonia. Rapid normalization of ammonia level ameliorates neurological outcome [1,2]. The first-line treatment for hyperammonemia in these patients is ammonia scavengers in combination with citrulline or arginine and high-calorie supplementation while controlling protein intake [1].