Although the exact cause of AS is unknown, we do know that genetics play a key role in AS. Most individuals who have AS also have a gene that produces a "genetic marker" - in this case, a protein - called HLA-B27. This marker is found in over 95% of people in the Caucasian population with AS, but the association between ankylosing spondylitis and HLA-B27 varies greatly between ethnic and racial groups. It is important to note, however, that you do not have to be HLA-B27 positive to have AS. Also, a majority of the people with this marker never contract ankylosing spondylitis.
A study published in Arthritis & Rheumatism examines the prevalence of HLA-B27 in the United States. The data used in the study comes directly from the Center of Disease Control's National Health and Nutrition Examination Survey (NHANES) program, which was also co-funded by the Spondylitis Association of America (SAA) and the Spondyloarthritis Research and Treatment Network (SPARTAN).
The study authors state that, "The age-adjusted US prevalence of B27 was 6.1%...By race/ethnicity, the prevalence of B27 was 7.5%...among non-Hispanic whites and 3.5%...among all other US races/ethnicities combined. In Mexican Americans, the prevalence was 4.6%."
One interesting note from the study's conclusion was that, "A decline in the prevalence of HLA–B27 with age is suggested by these data but must be confirmed by additional studies." Meaning that it appears that there appears to be a lower rate of HLA-B27 in older populations.
To read the study abstract, click here.
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