Rheumatoid arthritis (RA) is an autoimmune disease in which the body’s immune system mistakenly begins to attack its own tissues, primarily the synovium, the membrane that lines the joints. As a result of this autoimmune response, fluid builds up in the joints, causing joint pain and systemic inflammation.

RA is a chronic disease in which most people experience intermittent periods of intense disease activity punctuated by periods of reduced symptoms or even remission. In the long term, RA can cause damage to cartilage, tendons, ligaments and bones which can lead to substantial loss of mobility.

An estimated 1.5 million people in the United States have RA—almost 1 percent of the nation’s adult population. There are nearly three times as many women as men with the disease. In women, RA most commonly begins between the ages of 30 and 60. In addition, as many as 300,000 children are diagnosed with a distinct but related form of inflammatory arthritis called juvenile arthritis.