RESUMEN
OBJECTIVE: To investigate the risk of rheumatoid arthritis (RA) in the first degree relatives and to investigate whether the sex of the parent influences the pattern of inheritance. METHODS: An interview based case-control study, with subjects serially matched for age and sex. We analyzed 126 cases (hospital cases) and 94 controls (derived from the same hospitals), who gave information for family history of RA. Data concerning RA history among siblings and parents were computerized and analyzed univariately and multivariately. RESULTS: The odds ratio (OR) for developing RA is 4.4 (p < 0.001) if a first degree relative reported having the disease and 5.4 (p < 0.01) if a female first degree relative reported having the disease. For females the OR is 7.0 (p < 0.01) if the first degree relative is female. When the analysis was restricted to parents only, it was found that mothers with RA predispose their daughters and sons to develop RA more (OR = 8.6, p < 0.01, for daughters and 4.8, p < 0.05, for both sexes) than fathers (OR = 1.1 and 1.9, respectively). CONCLUSION: This case-control study confirms the familial clustering of RA and suggests that mothers confer susceptibility to RA on their offspring more often than fathers.