Rheumatic diseases in an Icelandic family. Clinical and immunological survey.

We have studied 192 members of a highly inbred Icelandic family with clustering of rheumatic diseases. Twelve consanguineous marriages are known in the family and 54 of 65 surviving offsprings of these (inbred group) were traced. Thirty-nine family members were affected by rheumatic diseases; 18 of them belonged to the inbred group. Eleven of 20 family members with rheumatoid arthritis (RA) came from the same inbred group. Eleven of the inbred group had a positive Rose-Waaler test for rheumatoid factor (RF) and the inbred group had significantly higher serum levels of IgG and IgM than an age and sex matched group from the family. Serum IgM RF was significantly associated with the age of the family members, but IgA RF and IgG RF did not show any such association. The possible role of recessive genes in the rheumatic diseases, as well as the inbreeding effect regarding certain extended HLA-complotypes is discussed.