Ankylosing spondylitis and the major histocompatibility system.

The purpose of this investigation was to see whether or not the hypothetical disease susceptibility locus to ankylosing spondylitis is linked to the MLC determinant 27a. Firstly, we discovered a strong MLC determinant which we called 27a because of its association with the second series specificity W27. Later, we found that this determinant was the same as that which Jorgensen et al. (1973) found to be associated with the second series specificity W5. These MLC determinants may, therefore, be in linkage disequilibrium with more than one HL-A specificity (in this case, of the second series) as previously described by Dupont et al. (1973). However, we found no association between 27a and ankylosing spondylitis. On the other hand, we confirmed the association of ankylosing spondylitis with W27 and also found an increase of HL-A2 of the first series which, however, was not statistically significant. In view of the high incidence of HL-A2 in the general population, more information is required to definitely establish such an association. We found no special association with specificities AJ and Hu (Sa 532), third series antigens, but confirmed their linkage disequilibrium with W27. Disease predisposition loci seem, therefore, to be associated with either type of MHS marker, multiple sclerosis and MLC determinant 7a, or ankylosing spondylitis and the second series antigen W27. It will be interesting to discover whether there is any special significance of the association of one marker rather than another.