What triggers ankylosing spondylitis?

[KeithD]

The exact cause of ankylosing spondylitis is not known, but it is believed to be related to a combination of genetic and environmental factors. Certain genes have been associated with an increased risk of developing the condition, but it is still unclear why only some people with these genes go on to develop ankylosing spondylitis. Other possible contributing factors include an overactive immune system, gut bacteria, and previous injury to the spine.