A Case of Phenylketonuria with Borderline Intelligence

Abstract

Phenylketonuria (phenylpyruvic oligophrenia), an hereditary molecular disease in man, is important as a type of mental deficiency whose genetics and biochemistry are sufficiently well-understood to indicate rational approaches to therapy. The condition is transmitted by an autosomal recessive gene which produces no known related mental signs in the heterozygous carriers (e. g., the parents of these patients).¹ The affected persons lack activity of a liver enzyme which normally oxidizes phenylalanine to tyrosine.² As a result, from birth, dietary phenylalanine accumulates at high levels in the blood and is converted to an abnormal metabolite found in the urine, phenylpyruvic acid. These two findings establish the diagnosis. The mental deficiency, typically of severe degree, is thought to be secondary to the accumulation of phenylalanine or its abnormal metabolites. This hypothesis is currently being tested by treatment with low phenylalanine diets.³ The present paper describes an otherwise typical case of