The KIAA1109-TENR-IL2-IL21 gene cluster, that encodes an interleukin (IL-21) that plays an important role in Th17 cell biology, is the 20th locus for which there is a genome-wide (P ≤ 5 ×10-8) level of support for association with RA. The gene discussed is ADAD1; the disease is rheumatoid arthritis.