von Willebrand factor and thrombotic thrombocytopenic purpura.

Recent advances in the understanding of platelet-dependent hemostasis and von Willebrand factor (vWF) functional regulation offer new insights into the pathogenesis of thrombotic microangiopathic disorders. The discovery of vWF-cleaving protease activity in normal plasma, and its deficiency in thrombotic thrombocytopenic purpura (TTP) patients, provides additional support for a pathologic role of ultra-large vWF in TTP. Although vWF-cleaving protease deficiency is highly prevalent among TTP patients, the defect has also been detected in individuals without active TTP. Therefore, vWF-cleaving protease deficiency appears to be an important risk factor for thrombotic microangiopathy rather than a specific diagnostic marker of TTP. Recent data indicate that vWF-cleaving protease activity correlates with clinical parameters in thrombotic microangiopathy patients. Therefore, determination of vWF-cleaving protease activity might prove useful in the future care of thrombotic microangiopathy patients and might be a rational basis for future classification of thrombotic microangiopathic disorders.