F5 and Rare hereditary thrombophilia: Inherited thrombophilia abnormalities recognized as independent risk factors for venous thromboembolism are represented by the common gain-of-function mutations in the coagulation factors V (G1691A, factor V Leiden, FVL) and II (prothrombin G20210A) and the rare lack-of-function deficiencies in the natural anticoagulant proteins antithrombin (AT), protein C (PC), and protein S (PS) [91].