Arginase deficiency is a rare autosomal recessive amino acid metabolism disorder characterized clinically by variable degrees of hyperammonemia, developing from about 3 years of age, and leading to progressive loss of developmental milestones and spasticity in the absence of treatment. The disease is arginase deficiency (Monarch Disease Ontology identifier MONDO_0008814). Also known as: argininemia, deficiency of canavanase, hyperargininemia.