Genetics play a large role in this condition. More than 90% of people with ankylosing spondylitis have a particular genetic marker called HLA-B27, which can be found on their white blood cells. This marker does not appear to be the only cause, however, as 80% of people with this genetic marker never develop an inflammatory disease. It is clear that some unidentified environmental trigger (and likely there is more than one type) plays a role in determining which people with this genetic marker end up developing ankylosing spondylitis.