ABSTRACT
Ankylosing spondylitis (AS) is one of the most common inflammatory rheumatic diseases, but estimates of its prevalence vary considerably, even in similar ethnic groups. The prevalence of AS generally varies with the prevalence of histocompatibility leukocyte antigen (HLA)-B27 (referred to as B27 hereafter), but determination of the precise prevalence in populations is affected by the sensitivity of the screening modality employed. Populations with a high prevalence of B27, such as Scandinavians and among the Inuit, Haida, and Bella Coola North American Indians, have correspondingly high levels of AS (1–3). In contrast, ethnic groups with a low prevalence of B27 such as Africans and Australian Aboriginals have a low prevalence of AS (4–7). Rare exceptions to this rule occur, as will be discussed subsequently. Estimates of the proportion of B27-carriers that develop AS also vary significantly, most likely related to the screening procedures that were used to identify cases. Where plain radiography was the screening modality, the prevalence of AS in B27-carriers has been estimated at 1.3–1.9%, whereas where magnetic resonance imaging (MRI) scanning was employed, the reported rate was 6.8% (8–12). Estimates of the overall prevalence of AS are similarly quite varied, ranging from 0.1% to 0.86% in Caucasian populations (9,12).
