Familial vs sporadic rheumatoid arthritis (RA). A prospective study in an early RA inception cohort

Objectives. To study potential differences in demographic, process and outc ome variables between familial and sporadic rheumatoid arthritis (RA) in an early RA inception cohort. Methods. In 1998, we ascertained the familial status of all collaborative p atients in a large early RA inception cohort at our department. Familial RA was defined by the presence of at least two siblings fulfilling the Americ an College of Rheumatology criteria for RA. Baseline demographic data and p rospectively recorded disease activity variables, therapies and radiologica l damage during the first 6 yr of disease were included in the analysis. A regression analysis was performed to assess whether familial clustering is a prognostic factor. Results. We identified 142 patients with sporadic and 36 with familial RA. The most striking difference between these groups was the larger sibship si ze in multicase families (8.2 +/- 2.5 vs 5.5 +/- 2.8; P < 0.0001). Age at o nset was similar in both groups, although males with familiar RA were young er at disease onset than those with sporadic RA (median 50 vs 57 yr; P = 0. 03). No differences were found in gender, presence of rheumatoid factor (RF ), antinuclear factor and HLA-DR typing or in disease activity, interventio ns and outcome over 6 yr of follow-up. Early radiological damage and diseas e activity, but not familial history of RA were prognostic for X-ray damage . Conclusion. We show that sibship size is the only relevant risk factor for familial RA. No differences in genotypic and phenotypic characteristics, di sease severity or radiological damage were observed among familial and spor adic RA. Familial history of RA is not a poor prognostic factor. This prosp ective study confirms previous cross-sectional findings in the Dutch popula tion.