Letters to the Editor

Dr. Dancis's letter underlines the complexities encountered in studying the various metabolic alterations resulting from a derangement of the internal environment as seen in phenylketonuria. It is a clinical fact that phenylketonuric individuals have diluted hair and iris pigmentation and that this defect is reversible by restriction in phenylalanine intake or supplementation of a normal diet by tyrosine. The inhibition by phenylalanine of tyrosinase derived from embryonic skin (Saunders, et al.), mushrooms (Dancis and Balis), or mammalian melanoma (Miyamoto and Fitzpatrick) suggests but one of several possible sites at which melanin formation may be inhibited in the phenylketonuric patient.