Though hypoxanthine is not a direct substrate for purine salvage production of ATP, enzymopathies in the pathway disrupt metabolic homeostasis; in the case of Lesch–Nyhan disease, HPRT deficiency results in the underutilization of hypoxanthine and xanthine, leading to the accumulation of urate and purine monophosphates. Here, HPRT1 is linked to Lesch-Nyhan syndrome.