For example, hyperuricaemia may act as a pro-oxidant, generating reactive oxygen species (ROS) and free radicals by inhibiting nitric oxide.28 In addition, elevated levels of xanthine oxidase, which are activated during UA metabolism, may produce ROS beyond the physiological range.29 These findings provide evidence supporting the possibility that UA levels above the solubility limit are harmful to the basal ganglia. Here, XDH is linked to hyperuricemia.