Uric acid:

Uric acid shown in above diagram is the major nitrogenous waste product of uricotelic organisms (birds, insects and reptiles), but is also established in ureotelic organisms from the breakdown of the purine bases from RNA and DNA. Some  individuals  have  a high  serum  level  of sodium  urate  (the  predominant form  of uric acid at neutral  pH) that  can lead to crystals  of this compound being deposited in the joints and kidneys and a condition known as gout, a kind of arthritis characterized  through extremely painful joints.

Figure:   Uric acid.