HPRT1 and Lesch-Nyhan syndrome: Hprt1, or hypoxanthine phosphoribosyltransferase 1, is an enzyme involved in the generation of purine nucleotides through salvage, and mutations in the human ortholog of the Hprt1 gene are causal for Lesch–Nyhan syndrome, which presents with an array of neurological and cognitive phenotypes.57