Tryptophan metabolism in a patient with phenylketonuria and scleroderma: a proposed explanation of the indole defect in phenylketonuria.

Phenylketonuria and severe focal scleroderma were observed in a white male child. This is the first instance in which the association of these two rare disorders has been reported. Studies carried out on this patient provide a possible explanation for the abnormalities of indole metabolism in phenylketonuria. On an unrestricted diet, when serum phenylalanine levels were elevated, excessive urinary excretion of indolic tryptophan metabolites was seen 18-24 hours after oral tryptophan loading, and tryptophan was demonstrable in the stool. This was not observed when the serum phenylalanine was within normal limits on a low phenylalanine diet. Impaired intestinal tryptophan absorption secondary to elevated serum phenylalanine, by providing tryptophan substrate for bacterial degradation to indolic compounds which are absorbed and excreted in the urine, may partially explain the abnormalities of indole metabolism in phenylketonuria.