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Protein Z Deficiency

By

Joel L. Moake

, MD, Baylor College of Medicine

Last full review/revision Jan 2021| Content last modified Jan 2021
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Because protein Z helps inactivate coagulation factor Xa, deficiency or dysfunction of protein Z predisposes to venous thrombosis (mainly in patients who also have other clotting abnormalities).

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 inactivates factor Xa on 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 Leiden) or an acquired autoantibody against a phospholipid-bound protein (an antiphospholipid antibody).

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.

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Overview of Thrombotic Disorders
Thrombotic disorders can be caused by genetic defects, which increase the risk of venous thromboembolism, or acquired defects, which increase the risk of arterial and venous thrombosis. Of the acquired causes, which of the following is most likely to increase a patient’s risk of venous thrombosis?
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