Carbamoyl-phosphate synthetase 1 deficiency (CPS1D) is 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 Monarch Disease Ontology entry MONDO_0009376 (carbamoyl phosphate synthetase I deficiency disease). Also known as: CPS I deficiency, CPS1 deficiency, CPS1D, carbamoyl phosphate synthetase deficiency, carbamoyl-phosphate synthase deficiency disease, carbamoyl-phosphate synthetase I deficiency, carbamoyl-phosphate synthetase deficiency, carbamoylphosphate synthetase I deficiency.