Risk of recurrent venous thrombosis in homozygous carriers and double heterozygous carriers of factor V Leiden and prothrombin G20210A.

BACKGROUND Homozygous or double heterozygous factor V Leiden and/or prothrombin G20210A is a rare inherited thrombophilic trait. Whether individuals with this genetic background have an increased risk of recurrent venous thrombosis is uncertain. METHODS AND RESULTS A case-control design within a large cohort of families with thrombophilia was chosen to calculate the risk of recurrent venous thrombosis in individuals with homozygosity or double heterozygosity of factor V Leiden and/or prothrombin G20210A. Cases were individuals with recurrent venous thrombosis, and controls were those with only 1 venous thrombosis. The cohort consisted of 788 individuals with venous thrombosis; 357 had factor V Leiden, 137 had prothrombin G20210A, 27 had factor V Leiden and/or prothrombin G20210A homozygosity, and 49 had double heterozygosity for both mutations. We identified 325 cases with recurrent venous thrombosis and 463 controls with only 1 venous thrombosis. Compared with noncarriers, crude odds ratio for recurrence was 1.2 (95% confidence interval, 0.9 to 1.6) for heterozygous carriers of factor V Leiden, 0.7 (95% confidence interval, 0.4 to 1.2) for prothrombin G20210A, 1.2 (95% confidence interval, 0.5 to 2.6) for homozygous carriers of factor V Leiden and/or prothrombin G20210A, and 1.0 (95% confidence interval, 0.6 to 1.9) for double heterozygotes of both mutations. Adjustments for age, sex, family status, first event type, and concomitance of natural anticoagulant deficiencies did not alter the risk estimates. CONCLUSIONS In this study, individuals with homozygous factor V Leiden and/or homozygous prothrombin G20210A or double heterozygous carriers of factor V Leiden and prothrombin G20210A did not have a high risk of recurrent venous thrombosis.