Phenylketonuria is due to deficiency of:

Ref. Textbook of Biochemistry for Medical Students. Page.300   Phenylketonuria
 Defect in Phenyl alanine Hydroxylase A variant, nonclassic PKU, is a result of a defective enzyme in tetrahydrobiopterin synthesis. Mental retardation Musty odor
 Microcephaly Diet low in phe
nyl-alanine Avoid aspartame
 Diet important during pregnancy to prevent complication in the kid