Previous studies showed that IL-23/Th17 pathway and increased expression of IL-17A as well as IL-17A gene polymorphism have been associated with various autoimmune diseases [17], such as primary biliary cirrhosis [18], inflammatory bowel disease [19, 20], rheumatoid arthritis [21–23] and ulcerative colitis [21, 24]. The gene discussed is IL17A; the disease is rheumatoid arthritis.