The cause of ankylosing spondylitis is unknown, but genetic factors seem to play a role. The disease starts with intermittent hip and/or lower-back pain that is worse at night, in the morning, or after inactivity. Back pain begins in the sacroiliac joint (between the pelvis and the spine) and may progress to include the lumbosacral spine and the thoracic spine (chest portion of the spine). Pain may be eased by assuming a bent posture. Limited expansion of the chest occurs because of the involvement of the joints between the ribs. The symptoms may worsen, go into remission, or stop at any stage. With progressive disease, deterioration of bone and cartilage can lead to fusion in the spine or peripheral joints, affecting mobility. It can be extremely painful and crippling. The heart, the lungs, and the eyes may also become affected. The disease most frequently begins between age 20 and 40, but may begin before age 10. It affects more males than females. Risk factors include a family history of ankylosing spondylitis and male gender. About 0.21% of Americans over age 15 are affected.
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