What Causes Ankylosing Spondylitis?

“There’s a very, very strong genetic component.”

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When someone gets diagnosed with a chronic health condition, such as ankylosing spondylitis (AS), one of their first questions might be, why did I get this? Did I do something wrong?

“There aren't any controllable risk factors that we know of,” says Eliana Cardozo, DO, assistant professor of rehabilitation medicine at Icahn School of Medicine at Mount Sinai. “Many people with ankylosing spondylitis either have another family member with it, or they have another family member that has some kind of rheumatologic or autoimmune condition.”

In other words, there’s a strong genetic component for AS, which is an inflammatory type of arthritis that causes increasing pain and stiffness in the lower back. This can be illustrated in the numbers: While it affects one percent of the general population, it’s slightly more common in those of northern European descent.

“There's a gene called HLA-B27 and it's the one associated with ankylosing spondylitis, [but] not everyone with that gene gets the disease,” says Dr. Cardozo.  In fact, fewer than one out of 20 people with the gene actually develop AS, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

The fact that some—but not all—people with the HLA-B27 gene get AS is a sign that there are some environmental factors involved in the development of AS—but researchers don’t know what they are yet.  

Additionally, AS is more likely, and also tends to be more severe, among men. “Some studies even show that it's two times as common,” says Dr. Cardozo.

If you know you have a family member with AS or another type of rheumatologic condition, and you notice you are starting to have symptoms of AS, such as pain in the low back that’s worse in the morning, you should see a physician for a physical examination. The earlier you begin treatment, the more likely you’ll see positive results from your treatments.

“The diagnosis of ankylosing spondylitis is what we call clinical diagnosis based on symptoms,” says Dr. Cardozo. If the patient has symptoms, the physician may also choose to do a blood test or imaging tests, which looks for signs of inflammation.  

Treatment for ankylosing spondylitis won’t just help you feel better in the short-term: It can also help reduce your risk of complications of AS, so if you suspect AS but haven’t yet seen your doctor, it’s worth the time to make the visit.