Anders Hammerich Riis

Background:  Venous thromboembolism has genetic determinants, but population-based data on familial risks are limited. Objectives:  To examine the familial risk of venous thromboembolism. Methods:  We undertook a nation-wide study of a cohort of patients with deep venous thrombosis or pulmonary embolism born after 1952. We used the Danish National Registry of Patients covering all Danish hospitals, for the years 1977 through 2009 to identify index cases of venous thromboembolism and assessed the incidence among their siblings. We compared standardized incidence ratios (SIRs) comparing the observed and expected number of venous thromboembolism cases among siblings, -using population gender- and age-specific incidence rates. Results:  We identified 30 179 siblings of 19 599 cases of venous thromboembolism. The incidence among siblings was 2.2 cases per 1000 person years, representing a relative risk of 3.08 (95% confidence interval (CI), 2.80 - 3.39) compared with the general population. The risk was higher for - men, SIR 3.36 (95% CI, 2.96 - 3.82) as well as women (SIR 2.81, 95% CI, 2.45 - 3.23). The risk was similar among siblings of index cases with venous thrombosis and those of index cases with pulmonary embolism. Conclusion:  Venous thromboembolism has a strong familial component.