Ankylosing spondylitis is a type of arthritis that affects the spine and sacroiliac joints. The sacroiliac joints connect the lower spine to the pelvis. Arthritis causes chronic inflammation, and in the case of ankylosing spondylitis, it can cause people to have less mobility, develop a hunched posture, or have pain in the spine and hips.
Ankylosing spondylitis affects about 1% of the U.S. population, or an estimated 3.2 million people. Worldwide, it’s thought to affect 0.1% to 1% of all people. So far, there’s no cure for ankylosing spondylitis, but doctors can manage the disease with medications and other treatments.
Epidemiology studies how diseases develop and what groups of people are likely to get certain diseases. By studying the epidemiology of ankylosing spondylitis, researchers and doctors hope to develop better treatments and prevention methods.
What Increases the Risk of Ankylosing Spondylitis?
Ankylosing spondylitis is one disease in a group of conditions called spondyloarthropathies. It’s the most common of these conditions. It’s also called axial spondylarthritis. Certain genes and other conditions related to the immune system can increase your risk for developing the disease.
The HLA-B gene is responsible for making a protein that helps the immune system recognize its own proteins versus viruses or bacteria. People with a variant of this gene, HLA-B27, are more at risk of developing ankylosing spondylitis. However, having the variant does not mean you will develop ankylosing spondylitis. Many people with the variant never develop the condition, and many people without the variant do develop the condition.
Other genes that affect the immune system are also associated with ankylosing spondylitis, including ERAP1, IL1A, and IL23R. Exactly how the genes and disease are connected isn’t yet understood.
People with ankylosing spondylitis may also have another inflammatory disorder, such as psoriasis, ulcerative colitis, or Crohn’s disease. People with a family history of these conditions or ankylosing spondylitis may also have a higher risk.
Ankylosing Spondylitis by Sex and Age
Ankylosing spondylitis symptoms most often begin before age 40, with some people experiencing symptoms before age 16. In teenagers or younger, it’s called juvenile-onset ankylosing spondylitis.
Men are more likely to be diagnosed with the condition than women. Men and women tend to have different symptoms, and women may go longer from the time symptoms start until they have a diagnosis. This may be in part because the disease is thought to affect men more often.
Men tend to have more spine damage that shows up on X-rays or other imaging scans than women. Women tend to have pain in the legs and arms, called peripheral arthritis.
Ankylosing Spondylitis by Race and Ethnicity
White people are more likely than other groups people to develop the condition. Ankylosing spondylitis is almost three times as common in white Americans than Black Americans or Africans. Mexican-Americans may have similar prevalence to whites, but there’s limited data so far to know for sure. It’s most prevalent in northern Europe and least common in sub-Saharan Africa.
White people with ankylosing spondylitis are more likely to have HLA-B27 than other ethnic groups. Latino people with the condition are also more likely to have the variant than Black people. Up to 90% of white people with ankylosing spondylitis have HLA-B27, compared with about 50% to 60% of Black people.
White people with the HLA-B27 variant tend to develop the disease at a younger age and are more likely to have a type of eye inflammation called anterior uveitis.
Despite being less likely to develop the disease, Black people with ankylosing spondylitis tend to have more severe disease.
For many people experience a long delay from the time they first start having symptoms and the time they get a diagnosis. This can be 8 to 10 years for some people, with women tending to have longer delays. Women may have a longer delay due to a continuing bias that AS is a disease for only men or because of a difference in symptoms compared to men, such as women often show less damage on an MRI.
Over time, ankylosing spondylitis can lead to some of the bones in the spine fusing together, which limits the ability to move. With treatment, some people may have flare-ups of inflammation in between times of remission.
If you have ongoing symptoms of ankylosing spondylitis, it’s important to talk to a doctor and advocate for imaging tests. This is especially important if you are less likely to develop the condition based on race or sex. Getting a diagnosis and treatment as early as possible leads to better control of the condition and better ability to keep up with daily activities.