Familial thrombophilia: genetic risk factors and management.

There are now a number of potential candidates for inherited thrombophilia but a definite causal relationship has been established for only a proportion of these. Accepted causes of familial thrombophilia include the factor V Leiden defect and the prothrombin 20210 G > A variant, as well as deficiencies of antithrombin, protein C and protein S. Together these inherited abnormalities account for 30-50% of individuals presenting with venous thromboembolism. Factor V Leiden, which is present in up to 7% of the European population, is the most common cause of familial thrombophilia. On a worldwide basis its prevalence varies greatly with ethnic origin. In common with other types of familial thrombophilia the frequency of factor V Leiden is highly dependent on the population group studied. Venous thromboembolism, present in approximately 55% of individuals with familial coagulation inhibitor deficiencies, is the predominant clinical manifestation of familial thrombophilia. There are indications that the venous thrombotic risk is somewhat less in those with factor V Leiden. The thrombotic risk is markedly increased in those with combined defects and in those who are homozygous for factor V Leiden. Risk factors for thrombosis include pregnancy, including the puerperium, surgery, oral contraceptive usage and prolonged periods of immobilization. A substantial proportion of venous thrombotic events may occur spontaneously, i.e. without an obvious precipitating event. The management of patients with familial thrombophilia comprises counselling, thromboprophylaxis and thrombosis treatment. Although the immediate treatment of an acute thrombotic event is not significantly different from that of patients without recognised abnormalities, detailed patient management is seriously hampered by a lack of appropriate clinical trials. Prospective clinical studies, designed to ascertain individual thrombotic risk and to evaluate different therapeutic strategies are urgently required.