OCCURRENCE OF RHEUMATOID-ARTHRITIS IS NOT INCREASED IN THE FIRST DEGREE RELATIVES OF A POPULATION-BASED INCEPTION COHORT OF INFLAMMATORY POLYARTHRITIS

Objective-To determine the risk of rheumatoid arthritis (RA) in first degree relatives of a true population based sample of probands with in flammatory polyarthritis. Methods-In a case-control study, a two stage screening procedure was used to ascertain the prevalence of RA in 518 first degree relatives of 207 Norfolk Arthritis Register cases regist ered in 1990 and 414 first degree relatives of 180 local controls. An initial joint symptom and medical history questionnaire was followed b y a physical examination, and serological and radiological evaluation of those with symptoms. Results-The prevalence of RA in the first degr ee relatives of all the Norfolk Arthritis Register cases was 7.7/1000, compared with 4.8/1000 in the first degree relatives of the controls, with a risk ratio of 1.6 (95% confidence interval 0.3 to 8.7). This v ery modest increase was also seen when the analysis was restricted to the first degree relatives of Norfolk Arthritis Register cases who sat isfied the American Rheumatism Association criteria for RA: prevalence rate 7.2/1000. Conclusion-There was no evidence of an important incre ased familial risk of RA in this community based sample. These data ar e compatible with others from immunogenetic studies showing only weak HLA associations with community ascertained RA.