Hyperphenylalanemia Without Phenylketonuria

Abstract

THE WIDESPREAD screening for phenylketonuria (PKU) among newborn infants has led to the recognition that not all instances of hyperphenylalanemia is caused by phenylketonuria.^1-5 At the present time, relatively little is known about the distribution of true PKU and of hyperphenylalanemia without PKU in newborns with elevated phenylalanine but normal tyrosine values in serum. Even less is known about the duration of this latter form of hyperphenylalanemia and whether these increased levels are harmful to mental development. Other than carrying out a long-term controlled study on the value of the lowphenylalanine diet in all infants with hyperphenylalanemia, which would be difficult to justify, the problem can be answered in part by examining the following: (1) the frequency of hyperphenylalanemia in the general population with normal intelligence; (2) the frequency of hyperphenylalanemia in the mentally-retarded population in institutions; and (3) the clinical and laboratory findings during early infancy of all