Family studies in RA - the importance of HLA-DR4 and of genes for autoimmune thyroid disease.

The segregation of HLA haplotypes with rheumatoid arthritis (RA) was studied in 13 selected, multicase families. HLA-DR4 was present in 77% of RA probands (32% controls). No single haplotype was associated with RA in different families. Analysis of HLA haplotype sharing in affected relatives showed no significant difference to the expected distribution. It seems likely therefore that the HLA-DR4 antigen itself rather than a linked susceptibility gene predisposes to RA. In 2 of 3 HLA-DR4 negative families, there were members with autoimmune thyroid disease. It is suggested that genetic susceptibility to RA may be associated with both HLA-DR4 and genes for autoimmune thyroid disease.