Although RA has been extensively researched, its cause is still unclear. Studies in families have shown that susceptibility to the disease is inherited. However, not every predisposed individual actually develops RA.

The causes of RA are still unclear, and our genes may be only partly to blame. For example, people carrying the genetic variant known as human leukocyte antigen (HLA) DR4 may be at increased risk of developing RA. This variation is manifested in white blood cells and plays a role in helping the body distinguish between its own cells and non-self invaders.