PROS1 and Rare hereditary thrombophilia: Hereditary thrombophilia constitutes a major risk factor for unprovoked VTE and its recurrence.[9] Various genetic defects have been identified to account for hereditary thrombophilia, including factor V Leiden, prothrombin G20210A mutation, protein C deficiency, and protein S deficiency.[10] The prevalence of pathogenic genes varies among different ethnic groups.