Recently, mutations in several genes that encode for coagulation proteins, such as the factor V (FV):R506Q (G1691A) mutation or the prothrombin (FII):G20210A variant, have been identified as important risk factors for developing a venous thromboembolism (VTE) (1). These mutations contribute to the development of thrombosis in ∼50% of all patients. The FV:R506Q (G1691A) mutation currently is considered the most important genetic risk factor for venous thrombosis. Although 5% of the healthy population carry the mutant allele, the prevalence of this mutation in patients with venous thrombosis is ∼40%. Compared with the wild type, heterozygous carriers of the mutation have an 8-fold higher risk and homozygotes have an 80- to 100-fold higher risk of developing a VTE (2). If and how this mutation contributes to arterial thrombosis is still under investigation, although recently Ardissino et al. (3) showed correlations among the factor V mutation, smoking, and myocardial infarction. The FII:G20210A variant, which is associated with increased prothrombin activity and increased plasma prothrombin, has been identified as an independent risk factor for thrombosis (4). Compared with individuals with the wild-type genotype, heterozygous carriers of the mutation have a 2.8- to 5-fold higher risk of developing VTE. The influence of the FII:G20210A mutation on arterial thromboembolic disease is not clear, but there is evidence that it is associated with cerebrovascular ischemic disease (5) and myocardial infarction (6). In addition to these two established thrombotic risk factors, the role of other genetic variations is still under investigation. The A223V (C677T) mutation in the thermolabile methylenetetrahydrofolate reductase (MTHFR) gene is associated with mild hyperhomocysteinemia. Homozygosity for the mutation may be associated with an increased risk for cardiovascular events. The …