Inherited factors in thrombosis.

Patients with inherited defects or abnormalities that impair the naturally-occurring anticoagulant and fibrinolytic systems are at risk of developing venous and, more rarely, arterial thromboembolism. The prevalence of inherited thrombophilia in the general population is higher than that of inherited bleeding disorders (ca. 1 in 7500 vs 1 in 20,000). Low levels or dysfunctional forms of antithrombin III, protein C and protein S and abnormal fibrinogens are the most frequent and well-established inherited causes for thrombosis. Less frequent and/or less established causes are low heparin cofactor II and plasminogen and high levels of plasminogen activator inhibitor and histidine-rich glycoprotein. The pathophysiology, genetic and clinical aspects and laboratory diagnosis of inherited thrombotic disorders are reviewed and an approach to prophylaxis and therapy is outlined.