Heterozygous protein C deficiency type I.

Protein C is a vitamin K-dependent plasma protein which has anticoagulatory and profibrinolytic properties as a result of inactivating coagulation factors Va and VIIIa and enhancing fibrinolysis. Heterozygous protein C deficiency is well known to be a risk factor for thromboembolic diseases. We here present a family with 16 members deficient in protein C, out of which only two persons were suffering from thromboembolic disorders. In patients suffering from heterozygous protein C deficiency thromboembolic complications in childhood are rare and are not obligatory in adults. These patients should therefore not be treated with oral anticoagulants unless thromboembolic complications have already occurred or are imminent. Coumarin anticoagulation implicates a serious risk of coumarin skin necrosis in protein C deficient patients during the initial therapeutic phase. This risk may be avoided by initiating coumarin therapy with low doses of the drug and in cases of thromboembolic complications by overlapping with heparin anticoagulation.