Protein S/Protein C Deficiency & Factor V Leiden

The risk of avascular necrosis (AVN) and pulmonary embolism (PE) is increased by having an inherited thrombophilia. This includes protein S or protein C deficiency and Factor V Leiden mutation. Protein S and protein C work on the anticoagulation cascade. Protein C, in addition to thrombomodulin which is found in the endothelial cells, will create an activated protein C. This activated protein C will work with protein S to inactivate factor number 5 and factor number 8 which lead to anticoagulation. Factor V Leiden mutation will produce Factor V that is resistant to inhibition by the activated protein C. Protein C will not be able to inhibit Factor V, and when you cannot inhibit Factor V, you will increase the risk of coagulation, resulting in DVT and PE. Protein S and protein C deficiency will decrease the ability to inactivate Factor V and Factor VIII, leading to a hypercoaguable state. Protein C is activated by the liver and blocks prothrombin from becoming thrombin. There will not be a clot. A combination of protein S and protein C together feedback and turn off the clotting by breaking down Factor V and Factor VIII. It is a control valve for clotting, and if you don’t have enough of them you will increase the chances of clotting because there is not enough of them to turn off the clotting mechanism well enough, and this increases the chance of clotting. The coagulation system is a series of chemical reactions that leads to a clot. The end result will be fibrin. Fibrin comes from fibrinogen with the help of thrombin. We need to control the hemostasis. We need to control the clotting system. If we lose control of the clotting system, we will end up with disseminated intravascular coagulation (DIC) or excessive clotting all over the boy, and the clotting factors will be exhausted, and we end by bleeding. The body controls homeostasis by having checks and balances. While the coagulation cascade helps in achieving homeostasis through different factors, there are other factors that will provide negative feedback to make sure that we do not clot continuously. Other factors will help in fibrin clot degradation. The negative feedback (anticoagulation) is provided by two factors: Antithrombin III and Protein S/Protein C. in the fibrin clot degradation, the plasminogen will become plasmin with the help of thrombin, and this will breakdown the fibrin clot (in order to control hemostasis). Plasmin breaks down the existing clots.

Thrombin stimulates antithrombin 3. Thrombin is in charge of everything. Thrombin is in control of making the clot. Thrombin activates plasminogen to plasmin, and the plasminogen causes fibrin clot degradation (breaks down the fibrin clot). Thrombin also stimulates the antithrombin III, which blocks the formation of Factor 10a, which blocks the formation of Thrombin, which blocks the clotting. Antithrombin 3 is like heparin. Heparin stimulates antithrombin 3. Protein S and protein C are factors that control hemostasis. They work as an anticoagulant through negative feedback. Protein S combines with Protein C, and together they help to control the blood clot formation. If these two proteins (Protein S/Protein C) are nonfunctional or deficient, the clot formation can go unchecked, unregulated, and there will be an excessive clotting condition. Protein S and Protein C can be one of the several inherited thrombophilias, a condition that leads to an increased risk for thrombosis and venous thromboembolism. You can test for Protein S, Protein C, and Factor V Leiden mutation when there are unexplained blood clots. Also, if the patient has a family history of blood clots especially if the patient is young. You are going to investigate for a possible blood clotting disorder. The patient must be off of Coumadin for at least two weeks or for 10 days after the episode.

Nabil Ebraheim, MD

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