MHC (major histocompatibility complex), which is found on chromosome 6. HLA-B27 has a gene locus of 6p21.3
-HLA-B27 is further complicated by containing 26 different alleles that encode for 24 different subtypes (HLA-B*2701 to HLAB*2725). B*2722 was excluded because it was found to contain the same sequence as B*2706. All of these varieties of HLA-B27, except 2, have been linked to AS susceptibility. The two that are not related to AS are B*2706 in South East Asia and B*2709 in Sardinia.
-HLA-B27 is part of a family of genes that are important in regulating the body's immune system.
-Having the HLA-B27 gene does not necessarily mean that you will have AS. In fact, in the caucasian population, only approximately 8% that carry the HLA-B27 gene have AS. And if there is no history of AS in the family, this 8% chance drops down to 2%. This means that other genes or factors must also play a role in susceptibility to AS.