Protein Z deficiency: a new cause of bleeding tendency.

Protein Z is a vitamin K-dependent plasma protein synthesized by the liver. Protein Z promotes the association of thrombin with phospholipid surfaces. So far, nothing is known about the clinical relevance of protein Z except alterations measured in patients under oral anticoagulant treatment. We propose that in protein Z deficiency a bleeding tendency might result because of the interaction of protein Z with thrombin on phospholipid endothelial surfaces. Therefore, we examined 36 patients with bleeding tendency of unknown origin, who were not under oral anticoagulant treatment and had normal liver synthesis function. Mean protein Z value of the patients with bleeding tendency was significantly diminished in comparison to the healthy control group. Twenty-one of the bleeding patients had lower protein Z levels than the lowest protein Z level of the control group. In conclusion, protein Z deficiency is described as a new type of bleeding tendency.