Acute neonatal citrullinemia type I is a severe form of citrullinemia type 1 characterized biologically by hyperammonemia and clinically by progressive lethargy, poor feeding and vomiting, seizures and possible loss of consciousness, within one to a few days of birth, with variable signs of increased intracranial pressure. The condition can lead to significant neurologic deficits. The disease is Monarch Disease Ontology id MONDO_0016600 (acute neonatal citrullinemia type I). Also known as: acute neonatal citrullinemia type 1, classic citrullinemia type 1, classic citrullinemia type I.