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Causes of Ankylosing Spondylitis

Although the exact cause of AS is unknown, it is known that genetics play a key role in AS. Most individuals who have AS also have a gene that produces a ‘genetic marker’ – in this case, a protein – called HLA-B27.

This marker is found in over 95% of people in the Caucasian population with AS (the association between ankylosing spondylitis and HLA-B27 varies greatly between ethnic and racial groups). It is important to note, however, that one does not have to be HLA-B27 positive to have AS. Also, a majority of the people with this marker never contract ankylosing spondylitis.

Scientists suspect that other genes, along with a triggering environmental factor, such as a bacterial infection, are needed to trigger AS in susceptible people. HLA-B27 probably accounts for about 40% of the overall risk, but then there are other genes working in concert with B27. There are probably five or six genes involved in susceptibility toward AS. It is thought that perhaps AS starts when the defenses of the intestines start breaking down and bacteria from the intestines pass into the bloodstream directly into the region where the sacroiliac joints are located.


  • The risk factors that predispose a person to ankylosing spondylitis include: testing positive for the HLA-B27 marker; a family history of AS; and frequent gastrointestinal infections. Unlike other forms of arthritis and rheumatic diseases, general onset of AS commonly occurs in younger people, between the ages of 17-45. However, it can affect children and those who are much older. AS is more common in men, but occurs in women as well.

  • The severity of AS varies greatly from person to person, and not everyone will experience the most serious complications or have spinal fusion. Some will experience only intermittent back pain and discomfort, but others will experience severe pain and stiffness over multiple areas of the body for long periods of time. AS can be very debilitating, and in some cases, lead to disability.

    Almost all cases of AS are characterized by acute, painful episodes (also known as ‘flares’) followed by temporary periods of remission where symptoms subside.

    It is important to know that ankylosing spondylitis is a chronic, or lifelong disease and that the severity of AS has nothing to do with age or gender. It can be just as severe in women and children as it is in men.

    Remember that even if you have AS and are experiencing only mild symptoms, which you are able to manage quite well, it is important to see your rheumatologist once a year in order to detect and treat any underlying complications.