F2 and Venous thrombosis: Some of this variation has been linked to Single Nucleotide Polymorphisms (SNPs); in particular, the non-synonymous SNP in the prothrombin gene (G20210G>A), which has been linked to elevated plasma levels of prothrombin (7) and increased risk of venous (7, 8) and arterial (9–11) thrombosis; and the Factor V Leiden mutation (F5 R506Q) that prevents activation of anticoagulant Protein C and thereby increases the risk of venous thrombosis (12–15).