Factor V Leiden and prothrombin gene mutation (G20210A) are the most commonly identified genetic defects that increase your risk for blood clotting. About 3% to 8% of people with ancestors from Europe have a copy of the factor V Leiden mutation. Only 1 in 5,000 people has two copies of the mutation. About 1 in 50 white people in America and Europe have the prothrombin mutation. Both of these mutations are less common in other populations.