[Study of a population carrying HLA B27 antigen compared with a population without B27, in the detection of ankylosing spondylitis].

Comparative study of 2 groups matched for age and sex, 39 subjects with B 27 and 40 subjects without B 27, chosen at random from blood donors, leads to the conclusion that the former complain of chronic low back pain and joint manifestations, and show a reduction in the range of movement of the lumbar spine, significantly more frequently than the latter. While radiological abnormalities of the sacro-iliac joints considered individually do not permit separation of those bearing the antigen from the controle, grouping them together shows that there are more cases of stage III sacro-ilitis among those with B 27. In all, 5 cases of spondylitis defined according to the New York criteria were found in this way in the group with B 27, 12.8 per cent as against 3 per cent in the controls. From these results, the incidence of rheumatic spondylitis can be estimated as between 0.8 and 1.7 per cent.