Although HLA-DRB1 is the main RA gene, it accounts for only part of the familial risk for RA. HLA-DRB1 alleles are neither necessary nor sufficient to cause the development of RA in a given individual. Several genome scans conducted in populations from France, Japan, North America and UK have confirmed the role of the HLA region and suggested several other susceptibility loci. Association studies support a role for several genes, including TNFR2, PADI4, SLC22A4, RUNX1, and PTPN22.