An estimated 2.1 million Americans are afflicted with rheumatoid arthritis (RA), a chronic and debilitating inflammatory disease of the joints.

American and Swedish researchers used blood samples of rheumatoid arthritis patients, along with blood samples from healthy patients, to compare DNA in search of small differences in the genetic code. Independently, both groups were led to a region of chromosome 9, containing 2 genes relevant to chronic inflammation. The researchers found that TRAF1 (encoding tumor necrosis factor receptor-associated factor 1) and C5 (encoding complement component 5) were likely candidates.

The whole-genome screening method helped researchers identify genes that contribute to disease-susceptibility without them imposing their preconceived notions of the disease. Researchers were thrilled to find out that TRAF1-C5 showed association by both American and Swedish groups. The independent research from both countries makes a strong case for the TRAF1-C5 association.

The TRAF1-C5 association is the third pair of chromosomal regions that have now been associated with rheumatoid arthritis. The previous two parings are HLA-DRB1 and PTPN22 and are well established for being associated with RA.

How TRAF1-C5 influences the risk of rheumatoid arthritis is not understood. It is not even known which of the 2 genes is causing the disease. As far as the researchers can tell both of the genes may be involved with RA. Both genes are known to control inflammatory processes that are relevant to rheumatoid arthritis.