What is Protein C Deficiency?

Protein C deficiency is a genetic trait that predisposes one to thrombotic disease, in which the blood clots too much, causing blood vessel blockages, or embolism. Protein C deficiency is associated with thrombosis in the veins, but not the arteries. The condition is very rare, affecting only 0.2 to 0.5% of the population.

Protein C is an anticoagulant, meaning that it prevents blood from clotting, or coagulating. Of course, clotting is a very important function of the blood, responsible for the healing of wounds. However, excessive clotting can cause problems of its own, including stroke and heart attack. Therefore, the body is naturally equipped with anticoagulant regulators, one of the most important of which is protein C.

There are two types of protein C deficiency. In Type I, the patient does not produce enough of the protein, while in Type II, the protein does not function correctly, interacting abnormally with other molecules. In most people with protein C deficiency, only one of the two genes responsible for protein C is dysfunctional, so there is still some functioning protein C in the blood.

Some people are born with two defective copies of the gene responsible for protein C, resulting in a complete deficiency of the protein. While this condition is extremely rare, it can lead to the development of purpura fulminans, also called purpura gangrenosa, in infants. This life threatening condition is characterized by the formation of numerous small clots within blood vessels, excessive bleeding, necrosis or tissue death, fever, and low blood pressure. Homozygous protein C deficiency, in which both the relevant genes are defective, must be treated very early with supplemental concentrates of protein C.

Heterozygous protein C deficiency, in which only one gene is defective, is usually treated by administering anticoagulant medication, such as aspirin, heparin, or warfarin. Such medications are typically taken regularly to prevent clotting, rather then in response to a thrombotic episode. Anticoagulant medication is usually prescribed long-term for people with protein C deficiency, often for life.

In a related, but extremely rare condition, the drug warfarin can induce protein C deficiency in patients who were not born with the condition. Though it is an anticoagulant, warfarin also inhibits protein C. In warfarin necrosis, excessive clotting prevents blood flow to the skin, resulting in lesions that eventually hemorrhage. Other anticoagulants do not have this issue, and they are sometimes given along with warfarin in the beginning of warfarin treatment to prevent warfarin necrosis.