Uric acid (UA) is the end product of purine metabolism in which adenosine, guanosine and inosine are broken down to form xanthine, which is converted to UA by xanthine oxidoreductase. In most mammals and other species, UA is further metabolized to allantoin by urate oxidase. In humans, a mutation to the UOx gene early in our evolution resulteprogred in an absence of functioning urate oxidase. In consequence, UA levels are as much as 10-fold higher in humans compared to other species (Alvarez-Lario & Macarron-Vicente. Rheumatology 2010;49:2010-2015).