Ankylosing spondylitis (AS) is relatively rare. Older data estimate that 0.1 to 1.4% of the global population have AS. The condition is more common in people with a gene known as HLA-B27.

The statistic above comes from a 2014 study.

AS is a type of chronic inflammatory arthritis. Early in the disease course, it causes low back pain and stiffness. Over time, it can cause fusion of the spinal vertebrae and significant mobility issues.

Treatment for AS focuses on symptom management and slowing disease progression. Treatment plans may include exercise, physical therapy, and lifestyle changes.

Continue reading to learn more about the prevalence of AS and who it affects.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Older data suggests that AS affects around 0.1 to 1.4% of the global population. In North America, AS affects around 31.9 people for every 10,000.

However, as this information is old and awareness of AS has increased over time, these figures may not be accurate, and the number of people with AS may be higher.

Learn more about AS here.

AS can affect anyone, but it is more common among certain groups. It has a strong genetic basis, for example. Experts have identified several genes that affect a person’s risk.

The strongest link is with the human leukocyte antigen (HLA)-B27 gene. Usually, HLA genes support the immune system and help it identify foreign viruses and bacteria.

Around 5–6% of people with the HLA-B27 gene have AS. While this percentage may appear quite low, it is many times higher than the general population.

The prevalence of HLA-B27 varies among different ethnicities, affecting:

  • 7.5% of non-Hispanic white people
  • 4.6% of Mexican-American people
  • 1.1% of non-Hispanic Black people

Individuals with a family history of AS are also more likely to have the HLA-B27 gene. However, people can develop AS without being positive for HLA-B27, and the strength of the connection between genetics and AS is not the same across ethnic groups.

For example, a 2017 study showed that Black people had more severe AS symptoms than white people, even though only 62.5% were positive for HLA-B27. In comparison, 85.3% of white people and 86.7% of Latino individuals had the HLA-B27 gene.

Overall, further research is required to understand the link between AS, genetics, and the social or environmental factors that may influence its onset and progression.

Learn about health inequity here.

Historically, experts believed that AS affected more males than females. However, a 2018 review indicates this might not be true. Previous studies have not included many females, and more recent research shows that the rates are more similar between sexes than scientists originally thought.

The condition also affects males and females differently. Females experience a higher frequency of other conditions associated with AS. These include enthesitis, psoriasis, and inflammatory bowel disease (IBD). Females also have significantly lower response rates to medications and report a lower quality of life.

In contrast, acute anterior uveitis is more prevalent in male individuals. This condition affects the eye and can cause pain and vision problems.

The differences in presentation and the rate of additional conditions between males and females may be due to differences in biology and medical treatment. For example, females experience more delays in receiving an AS diagnosis, which may affect health outcomes.

Learn more about AS in females here.

In addition to differences in AS between races, ethnicities, and sexes, there are also geographic differences. Experts are unsure why this is the case, but genetic, environmental, and lifestyle factors specific to each country could play a role.

The table below shows how many people have AS, on average, per 10,000 citizens in various countries. This data comes from an older 2014 review:

CountryPrevalence per 10,000 people
North America31.9

However, it is worth noting that these figures are estimates that may not translate to current populations, given increased geographic mobility and diagnosis.

Learn more about biases in healthcare here.

Doctors are unsure why some people develop AS while others do not. Although genes play a role, not everyone with a gene linked to AS will develop the condition. Similarly, a person does not have to have one of the genes to get AS.

Further research is needed to understand the link between genetics and AS fully.

Learn more about genes and their importance here.

AS is a serious disease for some people. AS typically begins with back pain and stiffness, which can remain stable for some time. But in one study, researchers found that 24.3% of participants had AS that progressed over the following 2 years.

More advanced AS can cause the spine to fuse and limit movement and physical activity. In some cases, AS can damage other organs in the body and cause complications.

AS has some effect on a person’s mortality, but this lessens with earlier diagnosis and effective treatment. However, it can co-occur with various other conditions that may be life threatening, such as cardiovascular disease, heart attacks, and stroke.

Therefore, it is important to talk with a doctor about any concerning symptoms. Early diagnosis and treatment are essential to managing AS and preventing serious complications.

Learn more about AS and its effects on the body here.

AS is an uncommon form of chronic inflammatory arthritis that affects the spine and other joints. In a 2014 study, around 0.1 to 1.4% of people globally had AS.

The prevalence of AS varies by age group, sex, race or ethnicity, and location and affects males and females differently. It is also more common in those who are positive for the HLA-B27 gene.