A rare and severe disorder of urea cycle metabolism most commonly characterized by either a neonatal-onset of severe hyperammonemia that occurs few days after birth and manifests with lethargy, vomiting, hypothermia, seizures, coma and death or a presentation outside the newborn period at any age with (sometimes) milder symptoms of hyperammonemia. The disease is due to mutations in the CPS1 gene (2p) that encodes carbamoyl-phosphate synthetase I (CPS1), an enzyme located in the mitochondrial matrix of hepatocytes and epithelial cells of intestinal mucosa that controls the first step of the urea cycle where ammonia is converted into carbamoyl-phosphate. Mutations in this gene lead to an interruption in the urea cycle and excess nitrogen is not converted to urea for excretion by the kidneys, leading to hyperammonemia. Inherited in an autosomal recessive manner. [from
SNOMEDCT_US]