Phenylpyruvic oligophrenia is an inherited disease characterized clinically by mental deficiency and the presence of phenylpyruvic acid in the urine. The phenylketonuria is a manifestation of an inborn error in the metabolism of phenylalanine.1 In normal persons this amino acid is almost entirely converted to tyrosine, a small amount only being converted to phenylpyruvic acid and phenyllactic acid. In phenylpyruvic oligophrenia, however, the conversion to tyrosine is largely blocked and the main metabolic pathway is by way of phenylpyruvic acid. This latter conversion occurs in the kidney and is apparently a slow process, since high levels of phenylalanine are reached in the plasma and cerebrospinal fluid.
It has been suggested that the mental defect in phenylpyruvic oligophrenia is due to intoxication by the accumulated phenylalanine or by an unidentified metabolite. Support for this viewpoint comes from recent reports from England of improved mental status in four patients with phenylpyruvic