What causes AS?
The cause of AS is unknown, but as genetic studies continue, researchers believe that the gene for Human Leukocyte Antigen B27 (HLA-B27) may be a significant factor. It is thought that HLA-B27 interacts with other proteins, altering the body's normal immune response.
HLA-B27 does not cause AS, but it is present in 90-95% of people who suffer from AS. However, just having the gene does not mean you will definitely get AS. Fewer than 25% of people with the HLA-B27 gene develop AS. For this reason, other factors besides HLA-B27 are thought to predispose you to AS. These may be genetic, environmental, and possibly even bacterial