HPRT1 and Lesch-Nyhan syndrome: Mutations in the gene encoding the purine biosynthetic enzyme Hypoxanthine phosphoribosyltransferase (HPRT) (IMP: pyrophosphate Phosphoribosyltransferase; EC 2.4.2.8) leads to both metabolic and neurological defects that can lead to Lesch-Nyhan Disease (LND).