Gout is a disorder of purine metabolism, and occurs when its final metabolite, uric acid, crystallizes in the form of monosodium urate. The blood deposits the crystals in joints, on tendons, and in the surrounding tissues. These crystals then trigger a local immune system inflammatory reaction. Uricase is required to breakdown uric acid. An evolutionary loss of uricase in humans and higher primates has made this condition more common.