What is ankylosing spondylitis (AS)?

Ankylosing spondylitis (pronounced ankle-oh-sing spon-dill-eye-tiss) is a form of arthritis that causes chronic (long-term) spine inflammation. Ankylosing spondylitis (AS) inflames the sacroiliac joints located between the base of the spine and pelvis. This inflammation, called sacroiliitis, is one of the first signs of AS. Inflammation often spreads to joints between the vertebrae, the bones that make up the spinal column. This condition is known as spondylitis.

Some people with AS experience severe, persistent back and hip pain and stiffness. Others have milder symptoms that come and go. Over time, new bone formations may fuse vertebrae sections together, making the spine rigid. This condition is called ankylosis.

How common is ankylosing spondylitis (AS)?

Ankylosing spondylitis belongs to a group of diseases known as spondyloarthropathies. Between three and 13 out of 1,000 Americans have one of these diseases.

Who might have ankylosing spondylitis (AS)?

Anyone can get AS, although it affects more men than women. Symptoms usually appear in people between the ages of 17 and 45. Ankylosing spondylitis has a genetic link and may run in families.

What causes ankylosing spondylitis (AS)?

About 95% of people who have AS have a variation of the human leukocyte antigen-B gene (HLA-B). This changed, or mutated, gene produces a protein called HLA-B27 that increases disease risk. However, most people with a mutated HLA-B gene don’t get AS. In fact, 80% of children who inherit the mutated gene from a parent with AS don’t develop the disease. More than 60 genes have been linked to the condition.

Having one of these conditions may also increase your risk:

What are the symptoms of ankylosing spondylitis (AS)?

Symptoms typically appear between the ages of 17 and 45 but may develop in younger children or older adults. Some people have persistent pain, while others experience milder symptoms. Symptoms may flare up (worsen) and improve (go into remission) off and on. If you have ankylosing spondylitis, you may experience:

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