Epidemiological and genetic aspects of IgM rheumatoid factors.
The occurrence of IgM rheumatoid factors (RF) was studied in a random sample of 8807 persons aged between 20 and 50 years in Tromsø, North Norway. Seropositivity for IgM RF was defined as a Waaler titre of 40 or more. A total prevalence of IgM RF of 1.36% was found, and a prevalence between 0.48-0.94% was found among the healthy persons, with no sex difference. Approximately 50% of IgM Rf positives are thus healthy. Only 11% of those with IgM RF suffered from rheumatoid arthritis. The majority of RF positive sera from healthy persons were low titred, and 81% of them converted to seronegativity in the course of 3.5 years. A low titred IgM RF appears rather harmless, while a high titre indicates a specific disease process. No association between IgM RF and DR4 could be found in healthy persons. The frequencies of Gm-allotypes a, b, e, f-n and x in healthy, RF positive individuals did not differ from the RF positive patients with RA, suggesting that the Gm-allotypes are not involved in the genetic pre-disposition for RA.
Husby
G
G
Department of Rheumatology, University Hospital of Tromsø, Norway.
Gran
J T
JT
Johannessen
A
A
D000328:Adult; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000235:genetics / Q000276:immunology; D006684:HLA-DR Antigens / Q000032:analysis; D015804:HLA-DR4 Antigen; D006801:Humans; D007129:Immunoglobulin Gm Allotypes / Q000032:analysis; D007075:Immunoglobulin M / Q000276:immunology*; D009017:Morbidity; D012016:Reference Values; D012217:Rheumatoid Factor / Q000032:analysis* / Q000096:biosynthesis; D012307:Risk Factors
D006684:HLA-DR Antigens; D015804:HLA-DR4 Antigen; D007129:Immunoglobulin Gm Allotypes; D007075:Immunoglobulin M; D012217:Rheumatoid Factor