HPRT gene mutation can cause HPRT enzyme activity defect, then it will lead to the surplus of its substrates hypoxanthine and guanine, and these surplus purines will be converted into UA under the action of xanthine oxidase (XO) (Fig. 1), resulting in the increase of UA levels in the body [29], and finally cause gout. The gene discussed is XDH; the disease is gout.