[Role of gene polymorphism in development of thromboses]

The development of thromboses is one of the most common causes of morbidity and mortality in the Western world. The perturbation of haemostasis is the central event in the pathogenesis of all thromboses. Most patients with thromboses have no recognisable associated haemostatic disorders. However, some patients do manifest hereditary hypercoagulable states, which contribute to the development of thromboses as well as other clinical manifestations, such as miscarriages and foetal complications. The major determinants of thrombosis include both environmental influences and genetic factors. Transient or long-lasting environmental influences may play important roles in arterial and venous thromboses. Haemostatic perturbance may also be genetically determined and exert a life-long influence. Specific mutations of genes predisposed to thrombosis, such as deficiency of antithrombin, protein C, or protein S, are found in relatively small number of families. In the absence of genetic deficiencies, thrombosis occurs in the older population, largely within the context of marked environmental influences (such as surgery, obesity, and malignancy). In contrast, familial thrombosis, associated with gene mutation, is associated with a younger age. The general importance of gene polymorphism was established after the recognition of activated protein C resistance (APCR) due to gene polymorphism G1691A in factor V (Factor V Leiden). This single gene defect increases the risk of venous thrombosis, without interaction with other genetic or environmental risk factors. The development of APCR led to many other investigations of gene polymorphism, such as prothrombin 20210, thrombomodulin, factors in the coagulation and fibrinolytic system, glycoproteins of platelet membranes, as well as polymorphism C677T of methylene tetrahydrofolate reductase. The number of potential genetic risk factors for occlusive thrombotic disease has increased significantly. Most of these gene polymorphisms increase the risk of venous thrombosis but there is no strong evidence of their influence as far as arterial thrombosis is concerned.