Familial aggregation of rheumatoid arthritis in The Netherlands: a cross-sectional hospital-based survey

Objectives. To study the familial aggregation of rheumatoid arthritis (RA) in The Netherlands and to analyse the effect of proband characteristics on the concordance rates for RA. Secondary aims were to compare the characteri stics of patients in an early RA inception cohort with those of regular pat ients and to select Dutch families for the genome-wide scan carried out by the European Consortium on RA families (ECRAF). Methods. A cross-sectional, hospital-based survey aimed to identify affecte d sibpair (ASP) families among our whole RA population. Familial RA, or an ASP family, was defined by the presence of at least two siblings fulfilling the 1987 ACR criteria for RA. Results. The estimated prevalence for familial RA was 9.8% and similar to t hat found in previous hospital series. The true-positive reporting rate for RA in sibs was 60%. Sibship size in ASP families (mean +/- S.D. = 7.8 +/- 3.3) was significantly larger than in the Dutch population. Probands with f amilial RA were more often rheumatoid factor positive and had a longer foll ow-up. Male gender and history of joint replacements were associated with h igher concordance rates for RA. However, regression analysis showed that, c orrecting for sibship size, the concordance rate for RA was largely not exp lained by proband characteristics. Compared to regular RA patients, our inc eption cohort encompassed more male and/or rheumatoid factor-negative patie nts, but had similar performance in the study and rate of familial aggregat ion. Conclusions. The familial aggregation of RA in The Netherlands is not incre ased and occurs preferentially in large sibships. Among proband characteris tics, sibship size is most clearly related to the recurrence of RA in parti cular families. Patients' recognition of RA manifestations in relatives is not optimal.