What is Predisposing factor for venous thrombosis and explain in detail?
Ref Harrison 16/e p686 , Robbins 7/e p 132 Hypercoagulability Hypercoagulability contributes infrequently to aerial or intracardiac thrombosis but is an impoant underlying risk factor for venous thrombosis. It is loosely defined as any alteration of the coagulation pathways that predis- poses affected persons to thrombosis, and can be divided into primary (genetic) and secondary (acquired) disorders (Table 3-2). Primary (inherited) hypercoagulability most often is caused by mutations in the factor V and prothrombin genes: * Approximately 2% to 15% of whites carry a specific factor V mutation (called the Leiden mutation, after the Dutch city where it was first described). The mutation alters an amino acid residue in factor V and renders it resistant to protein C. Thus, an impoant antithrom- botic counter-regulatory mechanism is lost. Heterozy- gotes carry a 5-fold increased risk for venous thrombosis, with homozygotes having a 50-fold increased risk. * A single-nucleotide substitution (G to A) in the 3'-untranslated region of the prothrombin gene is a fairly common allele (found in 1% to 2% of the general population). This variant results in increased prothrom- bin transcription and is associated with a nearly three- fold increased risk for venous thromboses. Less common primary hypercoagulable states include inherited deficiencies of anticoagulants such as anti- thrombin III, protein C, or protein S; affected patients typically present with venous thrombosis and recurrent thromboembolism in adolescence or early adult life. Congenitally elevated levels of homocysteine contribute to aerial and venous thromboses (and indeed to the development of atherosclerosis)