Phenylketonuria

Phenylketonuria (PKU), inborn error of metabolism, characterized by a virtual absence of phenylalanine hydroxylase activity and an elevation of plasma phenylalanine, that frequently results in mental retardation. Early and well-maintained treatment, which consists in limiting the phenylalanine intake of the child so that the essential amino acid requirement is met but not exceeded, makes normal development possible and prevents involvement of the central nervous system. Treatment must be intiated during the first days of life to prevent mental retardation. Some clinicians believe that treatment must be continued for life; others think that it can be terminated when myelinization of the brain is virtually complete, at about five years of age.