Biochemical basis of hypopigmentation:
Phenylalanine is competitive inhibitor of tyrosinase (key enzyme in melanin synthesis).
PKU
The most common deficiency is in phenylalanine hydroxylase (autosomal recessive) resulting in the classic picture of PKU.
Deficiency of dihydropteridine
reductase and 6-pyruvoyl-tetrahydropterin synthase, enzymes
necessary for the biosynthesis of tetrahydrobiopterin will also cause PKU. If unrecognized, the child will develop profound
mental retardation and impairment of cerebral function.
Treatment consists of dietary modifications with
limitation of phenylalanine intake and supplementation
of tyrosine.
The diagnosis of PKU and initiation of diet
modification needs to be implemented prior to 3 weeks of age to prevent mental retardation