Clinical and immunogenetic studies in multicase rheumatoid families.

We have studied HLA haplotypes, autoimmune diseases and circulating autoantibodies in 23 families with multiple cases of rheumatoid arthritis; 76 per cent of rheumatoid arthritis and 70 per cent of non-rheumatoid individuals were positive for HLA-DR4. The haplotypes Bw44-Bf*S-DR4; B40-Bf*S-DR4; and B15-Bf*S-DR4 were found in 13, 9 and 7 per cent of probands respectively and the B15-Bf*S-DR4 haplotype was found between four and five times more frequently in DR4-positive rheumatoid arthritis than in DR4 positive, non-rheumatoid arthritis families. Rheumatoid arthritis segregated with a DR4 positive haplotype in 13 families and with a DR4 negative haplotype in seven. Analysis of HLA haplotype sharing showed greater than random sharing by affected siblings which is in keeping with genes within the MHS influencing susceptibility to rheumatoid arthritis. Autoimmune thyroid disorders were seen in 8 per cent of family members investigated. They were significantly more frequent in those families in which rheumatoid arthritis segregated with a non-DR4 bearing HLA haplotype. This suggests that genes for autoimmune thyroid disease might predispose to rheumatoid arthritis independently of DR4. These genes are probably not HLA-linked, as there was no trend for HLA haplotype sharing to be increased in sibling pairs with either rheumatoid arthritis and thyroid disease or rheumatoid arthritis and thyroid autoantibodies respectively.