Activated Protein C is a serine protease which functions to inactivate Factors Va and VIIIa. Protein C is activated to Protein Ca when thrombin binds to thrombomodulin. Mechanisms of Inhibition A. Congenital deficiency of Protein C 1. There is normal level of Protein C, but decreased functional activity. Increased risk of thromboembolism, primarily deep venous thrombosis and pulmonary embolism.
Thromboembolic events begin in mid-late teenage years.
Homozygous patients often die of thrombosis in early infancy. Clotting is common in heterozygotes. In addition to the deep veins of the lower extremities, thrombosis can also occur in the cerebral veins, retinal veins, mesenteric veins, renal veins, and the inferior vena cava. Clotting may be further precipitated by surgery, trauma, pregnancy, or oral contraceptive use. Arterial thrombotic events are rare.