HGPRT deficiency with normal PRPP and APRT activity: 60

Abstract

A young man who presented with gout and urate overproduction (24 hour urine urate of 7.7 mmoles/24 hours on a low purine diet) was found to have an HGPRT activity of 9% of normal in an erythrocyte lysate. However the PRPP concentration was consistently normal in such lysates, a finding not previously recorded. In addition, the APRT activity in erythrocyte lysates was also normal, as was the PRPP synthetase activity. Lymphoblasts similarly showed 10% of normal HGPRT activity with a completely normal APRT activity. The incorporation of labelled hypoxanthine or adenine into intact erythrocytes was also normal. The normal APRT activity and the normal incorporation of purine bases into intact erythrocytes are consistent with, and possibly attributable to, the normal PRPP concentration. The question of the mechanism whereby the PRPP concentration can be normal in the presence of HGPRT deficiency will be proposed for discussion.