Protein Z serves as a cofactor for the downregulation of coagulation by forming a complex with the protein Z-dependent protease inhibitor (ZPI; 605271). Evidence also suggests that protein Z may promote the assembly of thrombin with phospholipid surfaces, thus enhancing coagulation. There is a wide variation of protein Z levels in human plasma, and studies have reported conflicting results of the clinical consequences of protein Z deficiency in humans. Most studies have reported an association between decreased protein Z levels and thrombosis, including stroke, venous thrombosis, and obstetric complications, although early reports suggested an association between protein Z deficiency and bleeding tendency (Kemkes-Matthes and Matthes, 1995). Overall, a role for protein Z in the pathogenesis of hemostatic disorders in humans is controversial and remains unclear (review by Broze, 2001 and Vasse, 2008).
Protein Z deficiency has been shown to exacerbate the thrombotic phenotype in patients with thrombophilia due to factor V Leiden (see 188055). [from
OMIM]