variant of the protein factor V (5), a clotting factor. Factor V Leiden gene is present in 3% of the general population. People who carry the factor V Leiden gene have a fivefold greater risk of thrombosis than the rest of the population. The factor V mutation (factor V Leiden) is the most common genetic cause of venous thrombosis. The factor V Leiden mutation causes resistance to activated protein C, yielding a defect in the natural anticoagulation system.
