Classical phenylketonuria is caused by a deficiency of
Classical phenylketonuria (hyperphenylalaninemia type I) → Deficiency of phenylalanine hydroxylase.
Atypical phenylketonuria (hyperphenylalaninemia type II and III) → Defect in dihydrobiopterin reductase.
Hyperphenylalaninemia type IV and V → Defect in dihydrobiopterin synthesis.
Phenylalanine transaminase
Phenylalanine hydroxylase
Tyrosine transaminase
Tyrosine hydroxylase