Prevalence of familial occurrence in patients with rheumatoid arthritis.

We studied 985 consecutive patients with definite or classical rheumatoid arthritis (RA) at an arthritis clinic, between April 1976 and August 1986, to investigate the prevalence of familial disease. We have demonstrated that at least 10.9% of unrelated patients with definite or classical RA have one or more first-degree relative(s) affected with definite or classical RA. Moreover, familial RA is not more severe than the more prevalent non-familial, i.e. sporadic, form of the disease.