Familial vs sporadic rheumatoid arthritis: a comparison of the demographic and clinical characteristics of 956 patients.

We studied the demographic, clinical, and disease severity characteristics of 96 patients with rheumatoid arthritis (RA) from multicase families (familial RA+) and 860 nonfamilial RA cases (familial RA-) seen consecutively in an outpatient rheumatic disease clinic between April, 1976 and August, 1986. Familial RA (+) and (-) cases were similar in essentially all demographic, clinical, and disease severity characteristics. Subgroups of 2nd generation patients with familial RA and sib-sib patients were similar, and neither group differed from the set of familial RA (-) individuals. The failure to find differential severity in these groups indicates that inferences from studies of families with RA may be extrapolated safely to patients with RA at large, but differences between rheumatoid factor positive (RF+) and RF (-) patients suggest that RA (+) and RF (-) patients should be analyzed separately.