HLA-DRB1 genes and extraarticular rheumatoid arthritis

The factors that trigger the development of extraarticular features of rheumatoid arthritis (RA) are still unknown. HLA-DR alleles such as HLA-DR4 and HLA-DR1 are associated with the risk to develop RA. A large scale study from Sweden and the Mayo Clinic suggests that HLA-DR4, but not HLA-DR1, is associated with the risk to develop extraarticular RA.