Thrombotic comlications are multifactorial disorders, with both hereditary and acquired risk factors. It is now clear that there are many genetic abnormalities that have an impact on increased risk of thrombophilia, and the cummulative presence of more than 1 abnormality further increases the risk of thrombosis. In hemostasis, there is a balance between procoagulant factors and natural anticoagulant proteins. The first genetic thrombotic disorders described were deficiencies of the natural anticoagulants, such as antithrombin, protein C, and protein S, but these abnormalities are rare, and are caused by many different mutations. More recently, single alleles that are relatively common in the general population have been described in procoagulant factors, such as factor V-Leiden and prothrombin mutation FII G20210A have an impact on increased risk for venous thrombosis. As more scientific scrutiny has been focused on the hemostatic system, further polymorphisms have been described. Thus, the current challenge is to transform this knowledge into the benefit for thrombophilic patients.

        Key words: hereditary thrombophilia, mutation FV-Leiden, mutation FII G20210A, protein S, protein C, antithrombin