<prompt> Classical phenylketonuria is caused by a deficiency ofPhenylalanine transaminasePhenylalanine hydroxylaseTyrosine transaminaseTyrosine hydroxylase  <response>: 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. 