disease responds to sapropterin phenylketonuria tetrahydrobiopterin-responsive hyperphenylalaninemia/phenylketonuria https://www.malacards.org/card/tetrahydrobiopterin_responsive_hyperphenylalaninemia_phenylketonuria tetrahydrobiopterin-responsive HPA/PKU BH4-responsive hyperphenylalaninemia/phenylketonuria Orphanet:293284 MONDO:0017389 BH4-responsive HPA/PKU GARD:0021166 MEDGEN:1842546 NANDO:2201077 UMLS:C5679945 Tetrahydrobiopterin-responsive hyperphenylalaninemia/ phenylketonuria (BH4-responsive hyperphenylalaninemia/ phenylketonuria) is a form of phenylketonuria (PKU), an inborn error of amino acid metabolism, characterized by mild to moderate symptoms of PKU including impaired cognitive function, seizures, and behavioral and developmental disorders, and a marked reduction and normalization of elevated phenylalanine concentrations after oral loading with tetrahydrobiopterin (BH4; sapropterin dihydrochloride), an essential cofactor of phenylalanine hydroxylase. NANDO:1200787