What Causes Ankylosing Spondylitis?

Ankylosing spondylitis (AS) is a chronic, debilitating, painful type of inflammatory arthritis that affects the spine. Researchers are still working to understand what causes AS. However, it is thought that a variety of factors increase one’s risk of the disease, including certain genetic and environmental factors. Men and young to middle-aged adults may also be more likely to get the disease.

Environmental Causes

Researchers speculate that there may be environmental contributors that increase one’s risk of AS. However, these are currently not well understood. Some of the environmental causes of AS may include:

• exposure to certain infections
• exposure to certain toxins
• mechanical stress/injury to the affected joints
• changes in the microbiome (the population of bacteria that inhabit your colon)
• inflammation of the bowel

Genetic Causes

People with variations of certain genes are more likely to get AS. One such gene variant is known as HLA-B27. The HLA gene is used to make an important protein for the immune system. Ninety percent of people diagnosed with AS test positive for the HLA-B27 variant.

Other genes are also thought to play a role in increasing one’s risk of AS, including a gene known as ERAP-1. Other genes involved with the immune system may also play important roles.

Physiological Causes

Researchers are still working to untangle the possible physiological contributors to AS. It is thought to at least partly arise from alterations in a person’s immune system. For example, researchers currently believe that an immune signaling molecule known as IL-17 may play an important role in the disease.

Other Risk Factors

For reasons that researchers don’t fully understand, AS is also more likely to occur in certain groups of people than in others. It is important to note that many people who do not have these risk factors get the disease as well.

You may be more likely to get diagnosed with AS if you are a male, Caucasian, and/or between the ages of 17 and 45.

While it used to be thought that AS predominantly affected men, in recent years it has become clearer that this may not be the case. It may be that almost as many women are affected by the condition as men.

It is possible that sex itself plays some sort of causal role in the disease. For example, a study in Arthritis and Rheumatism found some different patterns of immune responses in women with AS compared to men. This may point to some underlying physiological differences in how the disease appears in women.

Lifestyle Risk Factors

It's not known if smoking increases the risk of AS, though there is some evidence to suggest it may. However, it does seem to worsen existing disease symptoms.

Lack of exercise may be a risk for more severe disease. A daily exercise regimen can help keep you limber and strong, and decrease the disease's impact on your life. Strengthening certain muscles will allow you to maintain better posture, which can decrease your chance of the abnormal curving of the spine known as kyphosis.

Your healthcare provider or a physical therapist can suggest an appropriate exercise plan for you.

Ankylosing Spondylitis Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

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Summary

AS is a disease of multi-factorial causes which researchers are still trying to fully understand. It’s likely that various environmental and genetic factors come together to trigger the disease in any single person. Unfortunately, at this time, not much is known about how one might decrease one’s risk of getting AS.