Ankylosing spondylitis (AS) is a chronic inflammatory disease that causes stiffness of the joints, especially in the spine and sacroiliac joints. It most commonly affects young males. The cause is unknown but there is a strong genetic link to the HLA-B27 gene. It leads to inflammation and new bone formation between joints that fuses them together. Patients experience pain and stiffness in the lower back and hips that is worse in the morning and after periods of rest. Over time the spine can become hunched over as the joints fuse. Diagnosis involves x-rays showing changes to the sacroiliac joints and spine. Treatment focuses on NSAIDs, physiotherapy and exercises to improve mobility and posture.