In osteoarthritis (OA), the most common joint disease that can develop as a sequel of joint cartilage trauma [43] and evolve to cartilage and bone destruction, the role of complement was suggested 15 years ago [44] and still remains a promising field for investigation, since patients with OA had increased synovial fluid concentrations of C3a, which can be generated from all three pathways, compared to levels in healthy control subjects [19]. The gene discussed is C3; the disease is osteoarthritis.