Three mechanisms account for the hyperuricemia of Lesch-Nyhan syndrome. (1) The inability to salvage hypoxanthine and guanine permits increased conversion of hypoxanthine and guanine to urate (Figure 14-19). The rate of urate production is six times normal. (2) A deficiency in the salvage pathway leads to a decrease in IMP and GMP concentrations; this removes normal feedback inhibitors of the de novo pathway at the level of PRPP amidotransferase and PRPP synthetase (3) There is decreased utilization and an increase in the concentration of PRPP because less is used by the salvage pathway. The elevation of PRPP and the decline in feedback inhibitors stimulate the PRPP amidotransferase reaction and lead to a 200-fold increase in purine synthesis by the de novo pathway. It is unclear how altered purine nucleotide metabolism produces the signs and symptoms of the disease. Affected individuals are treated by physical restraint and with allopurinol. Allopurinol treatmet whose action is described next, has some beneficial effect on the hyperuricemia but not on the central nervous system symptoms. The prognosis is guarded, and the individuals usually succumb by 10 year of age.