Table 192 O Conditions Associated With Inherited Thrombosis

• Protein C deficiency

• Protein S deficiency

• Antithrombin deficiency

• Prothrombin G20210A

• Hyperhomocysteinemia

• Elevated factor VIII

• Factor XII deficiency hemostatic regulation in favor of increased risk of thrombosis.

Fibrinolytic Abnormalities

The function of the fibrinolytic system is the breakdown of fibrin clots. As in the coagulation system, the fibri-nolytic system is controlled by a specific group of inhibitors. Plasmin is an activated form of plasminogen and has a primary role in fibrin breakdown. Plasmin is inhibited by alpha-2-antiplasmin (the main inhibitor of plasmin), alpha-2-macroglobulin, alpha-1-antitrypsin, AT, and C1 esterase. Plasminogen activation is also inhibited by proteins such as plasminogen activator inhibitors I, II, and 3 (PAI-1, PAI-2, and PAI-3).3 A decrease in fibrinolytic activities, in particular decreased levels of tissue plasminogen activator (tPA) and elevated levels of PAI-1, results in impairment of fibrinolysis in vivo, resulting in arterial and venous thrombosis.1

Antithrombotic Factors (Coagulation Inhibitors)

Antithrombotic factors are plasma proteins that interfere with the clotting factors and therefore prevent thrombin formation and thrombosis. Three types of naturally occurring inhibitors are AT, prothrombin cofactor II, and protein C.


AT is a plasma protein made in the liver. AT neutralizes the activities of thrombin (IIa), IXa, Xa, XIa, and XIIa. The inhibitory action of AT against clotting factors is slow; however, its activity is markedly increased when AT binds to heparin (Fig. 19.2). AT deficiency is associated with thrombosis.1,2,4





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