Among these genetic risk factors, tyrosine phosphatase nonreceptor Type 22 (PTPN22) risk alleles [9], human leukocyte antigen D-related (HLA-DR) alleles [10], tumor necrosis factor–receptor associated factor 1 (TRAF1) and complement Component 5 (C5) [11], and interferon regulatory factor 5 (IRF-5) play crucial roles in RA susceptibility. The gene discussed is C5; the disease is rheumatoid arthritis.