Pathogenesis of idiopathic thrombotic thrombocytopenic purpura (TTP) caused by ADAMTS13 deficiency.

Multimeric von Willebrand factor (VWF) adheres to endothelial cells or to connective tissue exposed in the vessel wall. Platelets adhere to the VWF through platelet membrane glycoprotein GPIb. In flowing blood, VWF in the platelet-rich thrombus is stretched and cleaved by the metalloprotease ADAMTS13, limiting thrombus growth. If ADAMTS13 is absent, VWF-dependent platelet accumulation continues, eventually causing microvascular thrombosis and TTP.