"Type I phenylketonuria" is caused by a deficiency of
High-Yield Explanation
Hyperphenylalaninemias arise from defects in phenylalanine hydroxylase, EC 1.14.16.1 (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