What is Protein C Deficiency? Simple Answers to Basic Questions

Protein C deficiency is a blood coagulation disorder. Its chief characteristic is the predisposition to excessive blood clotting, especially in the deep veins of the legs. Protein C deficiency is a rare disorder, with an estimated prevalence of 0.2% of the general population. It is mostly hereditary, but may also be acquired. In some protein C deficiencies, there is an insufficient amount of protein C in the blood (quantitative deficiency). In other cases, the levels of protein C in plasma are normal, but the protein is dysfunctional and its activity is reduced (qualitative deficiency). Protein C deficiency can be mild and asymptomatic or severe and life-threatening.

2) What is protein C and what does it do?

Protein C is a vitamin K-dependent plasma glycoprotein. It is a major player in the complex biochemical reactions that, when an injury occurs, make blood clot, but only as much and for as long as necessary (hemostatic balance). Protein C is a coagulation inhibitor, i.e. an anticoagulant. Its role is to make sure that coagulation is kept under control, so that no excessive blood clotting occurs. In its activated form (aPC), protein C inactivates clotting factors Va and VIIIa (the "a" stands for "activated"). Activated protein C does not act alone: Protein S, another vitamin K-dependent glycoprotein, acts as cofactor to aPC and enhances its anticoagulant activity.

3) Where is protein C produced?

Protein C is produced in the liver. Vitamin K is vital to the production of protein C, and this is why protein C is called "vitamin K-dependent".

4) What causes protein C deficiency?

Hereditary deficiency of protein C is caused by a wide range (over 160) of genetic mutations. Acquired protein C deficiency may be triggered, for instance, by liver disease, vitamin K deficiency, warfarin (= anticoagulant and vitamin K antagonist) therapy, disseminated intravascular coagulation (DIC), certain chemotherapeutic drugs, etc.

5) What are the symptoms of protein C deficiency?

Deep venous thrombosis (predominantly of the legs) and pulmonary embolism are the main clinical manifestations of protein C deficiency. The severity and frequency of symptoms will depend on the severity of the condition. For example, in patients with severe congenital protein C deficiency, the condition will manifest itself within hours of birth with life-threatening (and all too often fatal) purpura fulminans and DIC. Patients with severe and moderately severe types of protein C deficiency are highly predisposed to thrombosis and DIC, especially when other risk factors are present (e.g. pregnancy/postpartum, infection, trauma, smoking, immobilization, surgery, etc.) Mild protein C deficiency may be free of symptoms, but not always. Again, a lot depends on additional risk factors, family history of thrombosis, underlying inflammation, etc.

6) How is protein C deficiency diagnosed?

There are special blood tests that measure the functional activity of protein C as well as the amount of protein C in plasma. Genetic testing is also available for family screening and prenatal diagnosis.

7) How is protein C deficiency treated?

Treatment will depend on the patient's level of risk for thrombosis, as predicted by the severity of the condition and the specific symptoms. The specialized physician will make decisions as to the need for preventative treatment, the duration of treatment (short- vs. long-term anticoagulation), and the choice of anticoagulant medications (e.g. heparin, low-molecular-weight heparins, warfarin (coumadin), protein C concentrate, fresh frozen plasma, etc.).

As with any medical condition, if you suspect you may have a blood disorder, please consult your doctor asap.

Sources:
http://emedicine.medscape.com/article/205470-overview
http://www.med.illinois.edu/hematology/PtProtC.htm
http://www.labtestsonline.org/understanding/analytes/protein_c_and_s/glance.html