tokens: A missense mutation has been identified in the human phenylalanine hydroxylase [ PAH ; phenylalanine 4 - monooxygenase ; L - phenylalanine , tetrahydrobiopterin oxygen oxidoreductase ( 4 - hydroxylating ) , EC 1 . 14 . 16 . 1 ] gene in a Chinese patient with classic phenylketonuria ( PKU ) .