Rheumatoid (ROO-muh-toyd) arthritis is a chronic disease in which various joints in your body are inflamed, leading to swelling, pain, stiffness, and the possible loss of function. Rheumatoid arthritis is unlikely to occur because of a single cause, but rather a combination of genetic and environmental factors that trigger an abnormal immune response. Bone tests on skeletons thousands of years old have indicated the disease dates back to ancient times. More than two million Americans, or 1 percent of the population, are estimated to suffer from rheumatoid arthritis. More than 60 percent of those suffering from the disease are women. The primary symptom of rheumatoid arthritis is morning stiffness that lasts for at least an hour. Symptoms such as fatigue, weight loss, and fever may also accompany early rheumatoid arthritis. Swelling and pain in the joints must occur for at least six weeks before an accurate diagnosis can be made. In about 20 percent of people with the disease, inflammation of small blood vessels can cause lumps under the skin. The condition, which can usually be detected through X-rays, can be treated with medication, rest, and exercise.