Experts don't know exactly how common ankylosing spondylitis is,
because the condition is often not diagnosed. The prevalence (how common it is)
differs among groups of people.
Ankylosing spondylitis is 2 to 3 times more common in men than in
women. Among white Europeans and North Americans, 7 in 10,000 men and fewer
than 2 in 10,000 women have ankylosing spondylitis.1
It is often found in certain ethnic groups, such as some Native American
tribes, Inuits, and Siberian Chukotkas. It is much less common in people whose
family is Japanese or African.2
The only clear risk factor for ankylosing spondylitis is having a
close family member who has the condition. About 15% to 20% of people with
ankylosing spondylitis have another family member who has it.2 Having a gene known as HLA-B27 and having frequent infections
of the gastrointestinal system (stomach and other organs of digestion) may also
increase your risk.2