von Willebrand factor and thrombotic thrombocytopenic purpura

Recent advances in the understanding of platelet-dependent hemostasis and v on Willebrand factor (vWF) functional regulation offer new insights into th e pathogenesis of thrombotic microangiopathic disorders. The discovery of v WF-cleaving protease activity in normal plasma, and its deficiency in throm botic thrombocytopenic purpura (TTP) patients, provides additional support for a pathologic role of ultra-large vWF in TTP. Although vWF-cleaving prot ease deficiency is highly prevalent among TTP patients, the defect has also been detected in individuals without active TTP. Therefore, vWF-cleaving p rotease deficiency appears to be an important risk factor for thrombotic mi croangiopathy rather than a specific diagnostic marker of TTP. Recent data indicate that vWF-cleaving protease activity correlates with clinical param eters in thrombotic microangiopathy patients. Therefore, determination of v WF-cleaving protease activity might prove useful in the future care of thro mbotic microangiopathy patients and might be a rational basis for future cl assification of thrombotic microangiopathic disorders. (C) 2000 Lippincott Williams & Wilkins, Inc.