A family study of ankylosing spondylitis.

Clinical, radiological and scintigraphic studies and HLA type assessment were performed in 38 subjects, constituting all the first-degree members of three generations of the families of six patients affected with ankylosing spondylitis (AS). The families included both parents, all siblings and all children of the probands. Definite AS was found in three men and possible AS in another. In another man and in a woman, a diagnosis of asymptomatic bilateral sacroiliitis was made. These six subjects indicate a family prevalence of AS reaching 15.8%. HLA B27 was present in 20 individuals (52.6%), including those with definite and possible AS and the case with asymptomatic sacroiliitis. The woman with asymptomatic sacroiliitis lacked HLA B27 antigen. Our study confirms the familial occurrence of AS, but it shows the occurrence to be lower than that previously reported.