F2 and antiphospholipid syndrome: Recently, a stratification of  major thrombophilic factors according to their risk of thrombosis has been published.[4] Based on this study the most thrombogenic factors are  deficiencies of natural coagulation inhibitors (antithrombin deficiency, protein C deficiency, protein S deficiency).[4]  Also, a high risk of thrombosis has been noticed in the case of antiphospholipid  syndrome and in the homozygous forms of factor V Leiden and prothrombin G20210A.