Lesch-Nyhan syndrome (LNS) is an X-linked recessive genetic disorder characterized by decreased hypoxanthine-guanine phosphoribosyltransferase (HGPRT) enzyme activity, leading to impaired conversion of hypoxanthine and guanine to inosine monophosphate (IMP) and guanosine monophosphate (GMP), respectively. The gene discussed is HPRT1; the disease is Lesch-Nyhan syndrome.