HPRT1 (Hypoxanthine Phosphoribosyltransferase 1): HPRT1 is an essential gene involved in purine metabolism. It catalyses the conversion of hypoxanthine to inosine monophosphate (IMP), a key precursor for purine nucleotide synthesis. Mutations in HPRT1 can result in Lesch-Nyhan syndrome, a rare genetic disorder associated with neurological and behavioural abnormalities.