Phenylketonuria (PKU) is the most common inborn error of amino acid metabolism and is characterized by mild to severe mental disability in untreated patients. The disease is phenylketonuria (Monarch Disease Ontology id MONDO_0009861). Also known as: PAH deficiency, PKU, hyperphenylalaninemia, non-PKU mild, phenylalanine hydroxylase deficiency, phenylalaninemia.