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Z-NUCLEOTIDE ACCUMULATION IN ERYTHROCYTES FROM LESCH-NYHAN PATIENTS: 190

5-Amino-4-imidazolecarboxamide riboside (Z-riboside) is an intermediate in the purine de novo synthetic pathway which may be metabolized either to IMP in a folate-dependent reaction or to the corresponding Z-nucleotides. Accumulation of ZTP in microorganisms has been associated with depletion of folate intermediates and has been postulated to play a regulatory role in cellular metabolism. We have demonstrated the presence of Z-nucleotides in erythrocytes derived from 5 individuals with the Lesch-Nyhan syndrome. Erythrocyte folate levels were within the normal range in these individuals, although GTP and GDP levels were significantly reduced below those in normal control (p<0.001). Lesser amounts of Z-nucleotides were found in 3 individuals with partial deficiency of the enzyme hypoxanthine guanine phosphoribosyltransferase and in 2 individuals with other disorders of purine overproduction. In contrast, no Z-nucleotides were detected in 13 normal controls or in 3 individuals with gout on allopurinol therapy. We conclude that Z-nucleotide formation may result from markedly increased rates of de novo purine biosynthesis. Whether or not the further metabolism of purine intermediates plays any role in the pathogenesis of the Lesch-Nyhan syndrome remains unknown.