Epidemiology and genetics of ankylosing spondylitis.

The spondyloarthropathies represent a group of disorders characterized by the presence of inflammatory peripheral and axial arthritis with sacroiliac involvement and a tendency to familial aggregation; prototype clinical syndromes are ankylosing spondylitis (AS) and Reiter's syndrome. The descriptive epidemiology of AS, including course and prognosis in patients cohorts, is reviewed. Particular attention is focused on the genetic epidemiology of AS, especially the evidence supporting causal association of disease with the class I histocompatibility antigen HLA-B27. In addition, analytical studies that support associations of infectious agents are reviewed. The spondyloarthropathies, especially AS and Reiter's syndrome, clearly illustrate the epidemiologic concept of host-environment interaction in the development and expression of disease.