HPRT1 and Lesch-Nyhan syndrome: HPRT1-related disorders are caused by deficiency of hypoxanthine-guanine phosphoribosyl transferase (HGprt), leading to uric acid overproduction and clinical features such as hyperuricemia, kidney stones, and gout as well as various neurologic and behavioral issues in the most severe phenotypes of Lesch-Nyhan disease (LND), which includes significant motor dysfunction, intellectual disability, and self-injurious behavior.