Ankylosing spondylitis (AS) is a type of arthritis that causes inflammation in the joints of the spine. The most common areas affected are the sacroiliac joints, which are the joints at the base of the spine that connect the spine and the pelvis, as well as the joints between the vertebrae. Other joints, such as the hips and shoulders, may also be similarly affected. AS causes pain, stiffness, and inflammation at the affected joints.
AS is the most common of the arthritis conditions known as spondylopathies. The second most common spondylopathy occurs in people with psoriasis.
About 1% of Canadians have AS. Having a family member with AS increases your risk of developing the condition, since the disease is at least partly hereditary. People with a certain molecule called HLA B27 on the surface of their cells are also more likely to get AS. Having both HLA B27 and a family history further increases your risk if a first-degree relative (e.g., a parent) has it. However, if you carry this molecule without a family history, the chance of getting this condition is lower. 90% of Caucasian patients with AS are HLA B27-positive, compared to only 50% of people of African descent. There is also thought to be an environmental risk, since if one identical twin has AS there is only a 50% chance that the other will have it.
AS affects about three times as many men as women, but it may be that the disease is less recognized among women. Most people are first diagnosed between the ages of 15 and 40 years. However, younger and older people can also be affected.