Background: Point mutations in the factor V gene (factor V Leiden) and the prothrombin gene (the substitution of A for G at position 20210) are the most common causes of inherited thrombophilia. Whether or not factor V Leiden increases the risk of recurrent deep venous thrombosis is controversial, and there is no information on the risk of recurrence among carriers of both mutations.
Methods: We studied a retrospective cohort of 624 patients who were referred for a first episode of deep venous thrombosis. After excluding 212 patients with other inherited or acquired causes of thrombophilia, we compared 112 patients who were heterozygous carriers of factor V Leiden with 17 patients who were heterozygous for both factor V Leiden and the prothrombin mutation and 283 patients who had neither mutation. The relative risk of recurrent deep venous thrombosis was calculated with use of a proportional-hazards model.
Results: Patients who were heterozygous for factor V Leiden alone had a risk of recurrent deep venous thrombosis that was similar to that among patients who had neither mutation (relative risk, 1.1; 95 percent confidence interval, 0.7 to 1.6; P=0.76). In contrast, patients who were heterozygous for both factor V Leiden and the prothrombin mutation had a higher risk of recurrent thrombosis than did carriers of factor V Leiden alone (relative risk, 2.6; 95 percent confidence interval, 1.3 to 5.1; P=0.002). When the analysis was restricted to patients with spontaneous recurrences (i.e., ones that occurred in the absence of transient risk factors for venous thrombosis), the risk among carriers of both mutations, as compared with carriers of factor V Leiden alone, remained high (relative risk, 3.7; 95 percent confidence interval, 1.7 to 7.7; P<0.001), particularly if the first event had also been spontaneous (relative risk, 5.4; 95 percent confidence interval, 2.0 to 14.1; P<0.001). In contrast, the risk of recurrence in the presence of transient risk factors was similar among carriers of both mutations and carriers of factor V Leiden alone.
Conclusions: The risk of recurrent deep venous thrombosis is similar among carriers of factor V Leiden and patients without this mutation. Carriers of both factor V Leiden and the G20210A prothrombin mutation have an increased risk of recurrent deep venous thrombosis after a first episode and are candidates for lifelong anticoagulation.