Arthritis Health Center

Understanding Ankylosing Spondylitis -- Basics

What Is Ankylosing Spondylitis?

Ankylosing spondylitis is a form of arthritis that mainly targets the spine. Over time, ankylosing spondylitis can cause your spine to become stiffer, and eventually the vertebrae (bones in your spine) may fuse together. People have a tendency to develop a stooped posture as the disease progresses. It affects 129 out of every 100,000 people in the U.S.

 Other joints areas that can be affected include shoulders, hips, and often tendons connected to bones, such as the heel. Severe disease may lead to poor posture and deformities. Inflammation of the eyes, called iritis, is common, and less frequently, scarring of the lungs, inflammation of the prostate, and inflammation of the aorta and aortic valve. 

While it was once thought that ankylosing spondylitis was mainly a male disease, it is now known that women get the disease too, with a ratio of 2 to 3 men for every woman. The disease in woman tends to be more atypical and affect the neck and limb joints. Most symptoms of ankylosing spondylitis start in early adulthood, before 40 years of age, although young men may have symptoms in early adolescence or, occasionally, in childhood.

What Causes Ankylosing Spondylitis?

The cause of ankylosing spondylitis is unknown, although research shows that people with this disorder are more likely to have a certain genetic marker called HLA-B27. If there is a close family history of ankylosing spondylitis (parents or siblings have it), and a person is also positive for the HLA-B27 marker, there is a 20% chance that individual will develop ankylosing spondylitis under the age of 40. The odds are much lower in those older than 40 years of age. 

Genetics is not the whole story. Environmental factors play a role, too because if one identical twin has the disease, the other twin will only develop ankylosing spondylitis 60% of the time.