Defective 5-Hydroxylation of Tryptophan in Phenylketonuria. ∗

Abstract

Summary

Untreated phenylketonuric patients excreted less serotonin and less 5-HIAA in their urine than did patients with mongolism. They also excreted less than a normal adult. The difference between phenylketonurics and the control subjects was accentuated after oral administration of tryptophan. When 5-HTP was given by mouth, the phenylketonuric subjects excreted relatively large amounts of serotonin. After their serum phenylalanine concentrations had been reduced to a normal level by the use of a low-phenylalanine diet, phenylketonurics spontaneously excreted normal amounts of serotonin and 5-HIAA. A reversible defect in the 5-hydroxylation of tryptophan thus seems primarily responsible for the decreased production of serotonin in phenylketonuria.