Although other joints can be involved, ankylosing spondylitis (AS) primarily affects the spine. In this particular type of arthritis, the joints and ligaments of the spine become inflamed. This can cause back pain and stiffness. In time, the bones may fuse together, making it difficult to bend and move. AS can affect other joints, and in some cases, it can damage the eyes, heart, or lungs.
According to University of Washington Orthopaedics and Sports Medicine, most people are diagnosed before the age of 35. The cause isn’t entirely understood, but people may have a genetic predisposition toward developing AS.
AS is a chronic disease, but most people continue to lead active lives. It rarely leads to severe disability. People with AS must pay special attention to posture and how they hold themselves. Daily exercise can help, and treatment generally revolves around symptom management.

Source: Healthline