Inherited mutations of a purine salvage enzyme, hypoxanthine guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8; MIM308000), give rise to Lesch-Nyhan syndrome (MIM300322) or HPRT-related gout called as Kelley-Seegmiller syndrome (MIM300323). In contrast with the most severe phenotype of classical Lesch-Nyhan disease (LND), the least severe phenotype is characterized by hyperuricemia without any neurological or behavioral abnormality, and designated HPRT-related hyperuricemia (HRH). In between these two extremes are phenotypes involving hyperuricemia and varying degrees of neurobehavioral abnormality but without self-injury, designated HPRT-related neurological dysfunction (HRND). Marked genetic heterogeneity of HPRT deficiency is well known. More than 300 different mutations in the HPRT gene (HPRT1 which located in Xq26.1), deletion, insertions, duplications, abnormal splicing and point mutations at different sites of the coding region from exons 1 to 9, have been identified.