<prompt> Enzyme defect in Classic PhenylketonuriaPhenylalanine hydroxylaseDihydrobiopterin reductaseFumarylacetoacetate hydrolaseHomogentisate oxidase  <response>: Hyperphenylalaninemias arise from defects in phenylalanine hydroxylase type I, classic phenylketonuria PKU, frequency 1 in 10,000 bihs, in dihydrobiopterin reductase types II and III, or in dihydrobiopterin biosynthesis types IV and V.Ref: Harper;s Biochemistry; 30th edition; Chapter 29 Catabolism of the Carbon Skeletons of Amino Acids 