Ankylosing spondylitis is a form of chronic arthritis that primarily affects the spine. It causes inflammation and stiffness of the spinal joints and surrounding tissues, which can eventually lead to a complete fusion of the spinal bones. The condition is strongly associated with the HLA-B27 genetic marker and tends to develop early, between ages 18-30. While the exact cause is unknown, genetics and immune system factors like tumor necrosis factor are thought to play a role. There is no cure, but treatments can help reduce symptoms, slow the progression, and manage pain.