How prevalent is Axial Spondyloarthritis among HLA B27 positive individuals, among HLA-B27-positive individuals who has a relative with AS, and among different ethnic groups?
The overall prevalence of AS in the general US population is 0.30% to 0.50%. Only 2% to 6% of HLA-B27-positive individuals develop AS during their lifetime. However, among those HLA-B27-positive individuals with an affected first-degree relative, the rate rises to 15% to 20%. AS is associated with HLA-B27 in all ethnic groups, which explains why the prevalence of AS corresponds to the prevalence of HLA-B27 in a particular ethnic group. Since the prevalence of HLA-B27 in northern latitudes is high (up to 15% of Scandinavians) and low (<1% of African blacks and Asians) in ethnic populations near the equator, there is an apparent decrease in the prevalence of AS going from the North Pole to the equator.