(I) Researchers are trying to understand better who gets rheumatoid arthritis and why. (II) They have discovered a genetic marker that is often associated with the earliest onset and most severe forms of the disease. (III) Yet not all rheumatoid arthritis sufferers have the marker (and vice versa) which makes scientists wonder whether rheumatoid arthritis is really a single disease. (IV) The most visible symptoms of rheumatoid arthritis are swollen joints and crippling stiffness, particularly of the hands and feet. (V) Environmental factors may also play a role, although no one knows whether the trigger is a virus, a bacterium or something else.