Disorders of Purine and Pyrimidine Metabolism

Abstract

Substantial progress has been made in the past year in identifying new primary disorders associated with abnormalities of purine and pyrimidine metabolism, in defining more precisely the metabolic consequences of specific enzyme defects, and in deducing the mechanisms involved in producing their clinical expression. A new primary cause of purine overproduction has been identified in children with a type of genetically determined immunodeficiency disease involving a primary T-cell dysfunction (Cohen et al., 1976; Wadman et al., 1977; Stoop et al., 1977). The condition, however, presents a curious metabolic paradox. Although the children overproduce purines, they produce virtually no uric acid and so can be conveniently identified by their marked hypouricemia and hypour-icuria. The resolution of the paradox is found in the metabolic site of their enzyme deficiency—a gross deficiency of the enzyme purine nucleoside Phosphorylase (PNP), which is responsible for processing purine ribosides to their free purine bases. As a consequence, the ribosides inosine and guanosine and the corresponding deoxyribosides replace uric acid as the end products of purine metabolism and are produced in a remarkable abundance quite comparable to the record degree of purine overproduction excreted as uric acid by children with the Lesch-Nyhan syndrome.