A severe ADAMTS13 insufficiency to <10% of its normal levels or activity results in a rare life-threatening disorder called thrombotic thrombocytopenic purpura (TTP), in which an abnormal accumulation of HMW-VWF multimers results in greatly increased platelet binding and the formation of thrombi that promote microvascular occlusion [18,19]. This evidence concerns the gene VWF and thrombotic thrombocytopenic purpura.