What causes ankylosing spondylitis?
The cause of ankylosing spondylitis (AS) is unknown. It is most likely a combination between genes and the environment that play a role in AS. The main gene associated with a risk for getting ankylosing spondylitis is called HLA-B27. This marker is found in greater than 95% of Caucasians and over 90% of all cases of AS, but you don't necessarily have to be a carrier of the HLA-B27 gene variant to have AS. Recently, variants in two other genes, called IL23R and ERAP1, have also been shown to carry a increased risk for AS. Similarly, just because you have the gene, does not mean you will develop AS. Bacterial infections are also suspected to be involved in AS. It is thought that AS may begin when the defenses in the gut (intestines) break down and bacteria enters your bloodstream near the SI joints.
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Is there a predisposition or cause for ankylosing spondylitits?
The genes HLA-B27, IL23R, and ERAP1 do not cause AS on their own. These genes represent a predisposition, or increased risk for developing ankylosing spondylitis. It is important to remember these genes do not cause AS by themselves. Risk factors that predispose a person to AS include testing positive for the HLA-B27 marker, a family history of AS, and/or frequent gastrointestinal infections.