Ankylosing spondylitis has no known specific cause, though genetic factors seem to be involved. In particular, people who have a gene called HLA-B27 are at an increased risk of developing ankylosing spondylitis. However, only some people with the gene develop the condition.

Ankylosing spondylitis  risk factors:

• Your sex. Men are more likely to develop ankylosing spondylitis than are women.
• Your age. Onset generally occurs in late adolescence or early adulthood.
• Your heredity. Most people who have ankylosing spondylitis have the HLA-B27 gene.

Complications of Ankylosing spondylitis:

In severe ankylosing spondylitis, new bone forms as part of the body's attempt to heal. This new bone gradually bridges the gap between vertebrae and eventually fuses sections of vertebrae. Those parts of your spine become stiff and inflexible. Fusion can also stiffen your rib cage, restricting your lung capacity and function.

Other complications might include:

Eye inflammation (uveitis). One of the most common complications of ankylosing spondylitis, uveitis can cause rapid-onset eye pain, sensitivity to light, and blurred vision. See your doctor right away if you develop these symptoms.

Compression fractures. Some people's bones thin during the early stages of ankylosing spondylitis. Weakened vertebrae can crumble, increasing the severity of your stooped posture. Vertebral fractures can put pressure on and possibly injure the spinal cord and the nerves that pass through the spine.

Heart issues. Ankylosing spondylitis can cause problems with your aorta, the largest artery in your body. The inflamed aorta can enlarge to the point that it distorts the shape of the aortic valve in the heart, which impairs its function.