Do Genetic Contributors to Warfarin Responsiveness or Common Thrombophilias Influence the Risk of Major Bleeding in Patients on Extended Duration Vitamin K Antagonist (VKA) for Venous Thromboembolic Disease?

Background: Recent studies have indicated that genetic factors such as polymorphisms in the CYP2C9 and the VKORC1 genes play an important role in vitamin K antagonist (VKA) response and perhaps bleeding. There are also data to suggest, especially for factor V Leiden, that thrombophilia may confer a decreased risk of bleeding (which could explain its persistence and high prevalence in the population). The influence of major genetic factors on risk of bleeding have not previously been evaluated in large prospective cohort studies of patients with VTE on extended (treatment after the first 3 to 6 months) VKA therapy.

Aims: We sought to determine the effect of genetic variants that influence warfarin metabolism and thrombophilias on the rates of major bleeding during extended VKA therapy in patients with VTE disease.

Methods: The Bleeding Risk study is a multicentre, multinational prospective cohort study of patients on extended VKA for unprovoked VTE, or provoked VTE with prior VTE. Patients were enrolled after at least 3 months of VKA. All major bleeding events during long term VKA were captured and adjudicated. A blood sample was taken from each patient at their first study visit and analysed in a central lab to identify the following genetic variant types: CYP2C9*2 (C/T), CYP2C9*3 (T/G), 1639G-A (G/A), Factor V Leiden (G/A: FVL), CYP4F2 (G/A), and Prothrombin gene 20210 variant (PGV). Rates of major bleeding were then evaluated for patients with each genetic variant in isolation and in combination.

Results: 2290 of the 2514 patients enrolled at 12 sites have contributed over 7000 years of observation and were included in this analysis. The mean patient age was 60.2±14.7 years, 64% were male, 92% Caucasian, average BMI was 31.3, and 9% of patients were on antiplatelet agents. Patients were followed for a mean of 2.8 years (range, 0.1 to 6.8 years. 121 patients (4.8%) experienced at least one episode of major bleeding. The annual rate of bleeding was 1.7 per 100 patient-years of observation. The CYP2C9*2 variant heterozygous/homozygous versus wildtype (476 patients vs 1584) was protective against bleeding (Incidence risk ratio 0.5, p =0.01), CYP2C9*3 variant heterozygous/homozygous versus wildtype (215 patients vs 1845) was associated with major bleeding (Incidence risk ratio 2.0, p =0.01), VKORC1 and CYP4F2 had no association with major bleeding, and CYP2C9*3 variant heterozygous/homozygous in combination with wildtype CYP2C9*2 (186 patients) was associated with major bleeding (Incidence risk ratio 3.24, p =0.02). Both FVL (19% of patients) and PGV (8% of patients) had no effect on major bleeding, with p values > 0.35 for comparison of the wildtype to heterozygous/homozygous.

Conclusion: This is the largest study we are aware of to determine if warfarin metabolic genotype variants and common thrombophilias influence major bleeding risk in patients followed long-term with extended duration VKA therapy for VTE. The thrombophilias do not influence bleeding risk but those with CYP2C9*3 hetero/homozygous inheritance had double the risk and CYP2C9*2 hetero/homozygous inheritance half the risk. There appears to be an interaction between the CYP2C9*2 and *3 genotypes.