hematology and oncology
Protein Z Deficiency
Introduction
Because protein Z helps inactivate coagulationfactor Xa, deficiency or dysfunction of protein Z predisposes to venous thrombosis (mainly in patients who also have other clotting abnormalities). (See also Overview of Thrombotic Disorders .) Protein Z, a vitamin K–dependent protein, functions as a cofactor to down-regulate coagulation by forming a complex with the plasma protein, Z-dependent protease inhibitor (ZPI). The complex predominantly inactivatesfactor Xaon phospholipid surfaces. The consequence of protein Z or ZPI congenital deficiency, or of acquired autoantibodies to protein Z, in the pathophysiology of thrombosis, fetal loss, and cancer (ovarian or gastric) is not completely clear; however, a defect of either protein Z or ZPI may make thrombosis more likely if an affected patient also has another congenital coagulation abnormality (eg, Factor V Resistance to Activated Protein C (APC) ) or an acquired autoantibody against a phospholipid-bound protein (an Testing for protein Z deficiency is not part of routine thrombophilia testing. Quantification of protein Z, ZPI, and protein Z autoantibodies is done in specialized regional laboratories by plasma electrophoresis, immunoblotting, and enzyme-linked immunosorbent assay. It is not yet known whether anticoagulant therapy or prophylaxis is indicated in protein Z or ZPI deficiency. 