The extreme interest which has been shown in the use of special diet in the attempt to control or prevent nervous system degeneration associated with phenylketonuria may be due to the obvious fact that at present no other practical approach to the problem exists. The rather widespread discussion of the difficulties associated with treatment of the phenylketonuric has led to more extensive testing for the disorder and concomitant more accurate and early diagnosis.
Transmitted as a recessive hereditary trait apparently linked with blondism,1 phenylketonuria results from the inborn failure of the organism to hydroxylate phenylalanine to tyrosine. The accumulated phenylalanine is partially deaminated in the kidney and excreted in the urine as phenylpyruvic acid, phenyllactic acid, and phenylacetic acid. The plasma concentration of phenylalanine in the normal human is approximately 1.4 mg. per 100 cc. Plasma levels of phenylalanine in the phenylpyruvic person are found to be 20 to