Hypoxanthine - guanine phosphoribosyltransferase (HPRT) is a purine salvage enzyme that plays a key role in the regulation of purine metabolism in man. Interest in this X-linked enzyme stems, in part, from the existence of two clinical syndromes associated with deficiency of HPRT enzyme activity. In 1967, Seegmiller et al1 described a virtually complete deficiency of HPRT activity in patients with the Lesch-Nyhan syndrome. This syndrome is characterized by an overproduction of uric acid as well as a bizarre constellation of neurologic and behavioral abnormalities, including mental retardation, spasticity, choreoathetosis, and a compulsive form of self-mutilation. A partial deficiency of HPRT was subsequently demonstrated in several male patients who presented with hyperuricemia and a severe form of gout at an early age.2 This latter group of patients is usually free of the central nervous system manifestations that characterize the Lesch-Nyhan syndrome, although an occasional patient with partial HPRT deficiency