Hyperphenylalaninemia is due to defect in the enzyme:
a. Phenylalanine hydroxylase(Ref: Nelson's 20/e p 636-636)Deficiency of the enzyme phenylalanine hydroxylase or of its cofactor tetrahydrobiopterin (BH4) causes accumulation of phenylalanine in body fluids and in the brain.
Phenylalanine hydroxylase:
Tyrosinase
Homogentisic acid oxidase
Ornithine transcarbamylase
Inborn Errors of Metabolism