95% of Caucasian AS patients have a special gene that produces a so-called genetic marker, a protein called HLA-B27. It should be noted that the relationship between AS and HLA-B27 differs significantly between races and ethnicity. Also, Caucasians without HLA-B27 still carry a risk of developing AS just as wells as people with the gene doesn't necessarily develop the condition.
Why do we get ankylosing spondylitis?
It is believed that other genes may play a role in the development of AS. But not only do you have to have the right (or wrong) genes, they also need to be triggered by environmental factors. So two people predisposed with AS and with the exact same predisposition would not necessarily both get AS. It depends on their environment and lifestyle.
Scientists believe that there might be five or six genes involved in the predisposition for AS.
The biggest risk factors predisposing a person to AS are:
- Having the protein HLA-B27.
- Family history of AS.
- Frequent gastrointestinal infections.
Source : Spondylitis Associatin of America