HPRT1 and hyperuricemia: Both Hypoxanthine-Guanine Phosphoribosyl Transferase (HGPRT) and glucose-6-phosphatase deficiencies can cause accumulation of 5-Phosphoribosyl-Alpha-Pyrophosphate (PRPP), which is used in the salvage pathway of hypoxanthine, xanthine and guanine, adversely leading to hyperuricemia.