HPRT1 and Lesch-Nyhan syndrome: Lesch-Nyhan syndrome (LNS) is a rare X-linked recessive disorder caused by mutations in the hypoxanthine-guanine phosphoribosyltransferase (HPRT) 1 gene, which is involved in the purine salvage pathway.[1,2] It is diagnosed when HPRT enzyme level is <1.5% of normal in males.[3] LNS can fully develop with uric acid overproduction, neurocognitive disability, and characteristic compulsive self-injurious behavior.