Gas-liquid chromatography of phenylalanine and its metabolites in serum and urine of various hyperphenylalaninemic subjects, their relatives, and controls.

Phenylalanine and its metabolites were determined in serum and urine of phenylketonuric subjects and in subjects with milder hyperphenylalaninemia in whom blood phenylalanine concentrations were usually less than 200 mg/liter. Metabolite concentrations were related to serum phenylalanine, and in hyperphenylalaninemic subjects were between those for treated and untreated phenylketonuric subjects. Phenyllactic and phenylpyruvic acids were excreted by all of the mild hyperphenylalaninemic subjects except for the youngest (one-year-old twins) and the only subject with a serum phenylalanine of less than 100 mg/liter. Serum and urinary metabolites of heterozygotes of both conditions were similar before and after a phenylalanine load. The similar pattern of metabolites in phenylketonuric and mild hyperphenylalaninemic subjects reinforces the belief that the latter have some phenylalanine hydroxylase activity, and that this is the essential difference between the two groups.