HEREDITARY THROMBOPHILIA AND VENOUS THROMBOEMBOLISM

The hereditary thrombophilias are a group of inherited conditions that predispose to thrombosis. Heritable deficiencies of the endogenous an ticoagulants protein C, protein S, and antithrombin have been recogniz ed for some years, but their prevalence, even among patients with fami lial thrombosis, is low. The recent discoveries of two relatively comm on thrombophilias, resistance to activated protein C associated with a n abnormal factor V gene (factor V Leiden), and prothrombin gene varia nt 20210A, have substantially increased the likelihood of identifying a heritable predisposing factor in patients with thromboembolism Modes tly elevated levels of plasma homocysteine, which are in part genetica lly determined, have also recently been associated with an increased r isk for Venous thromboembolism. A predisposition to thrombosis can now be identified in a substantial minority of patients with venous throm boembolism, and in the majority of patients with familial thrombosis, and there is accumulating evidence that multiple coexisting defects ar e present in persons with the most marked tendency to thrombosis. The most common causes of hereditary thrombophilia are reviewed with an em phasis on resistance to activated protein C, prothrombin variant 20210 A, and hyperhomocystinemia, and the current status of laboratory testi ng for thrombophilia is discussed.