[Phenylalanine metabolites in hyperphenylalaninemic children]

Phenylalanine and its organic acid derivatives, phenylacetate, mandelic, o-hydroxy-phenylacetate, phenyllactate and phenylpyruvate are increased due to the enzymatic block in the normal pathway of phenylalanine metabolism in phenylketonuric and hyperphenylalaninemic patients. These organic acids are neurotoxic and whether they are responsible for behavior and learning problems in hyperphenylalaninemic children remains to be seen. The purpose of the present study was to evaluate: 1) variations of the organic acid derivatives of phenylalanine during dietary treatment and 2) the usefulness of its determination to further adjust the phenylketonuric diet. Twenty-eight children, ages 4 months to 16 years, were studied. On the same day, the level of phenylalanine in the plasma and phenylalanine metabolites in freshly collected urine samples were tested. Phenylalanine metabolites were detected in some patients with blood phenylalanine levels below 242 microM/L and they rose as levels of blood phenylalanine increased with the phenylpyruvic acid being the highest when blood phenylalanine levels were greater than 424 microM/L. These compounds are usually not detected in normal urine. However, we have or learning problems, thus we do not make further adjustments in the PKU diet on the basis of phenylalanine metabolites.