HLA haplotypes in a family with ankylosing spondylitis and rheumatoid arthritis.

HLA haplotypes (including A, B, C and DR loci) were studied in a family with members who had both rheumatoid arthritis (RA) and ankylosing spondylitis (AS). Sacroiliitis was found in 7 family members, one of whom had AS and 2 others erosive, seropositive RA. They carried the B27-DR4 haplotype, suggesting a possible dual genetic association of the same haplotype in both RA and AS. Three other different HLA-B27 containing haplotype were found, 2 of which could be associated with sacroiliitis/AS. Within this family sacroiliitis and/or AS rather seemed associated with the B27 antigen itself than with the same haplotype.