Cleavage of VWF by ADAMTS13 is an important step in the regulation of VWF activity and any perturbation in the delicate balance between too little or too much cleavage leads to pathologic consequences: hemorrhagic when cleavage is excessive as is the case for VWD type 2A or thrombotic consequences when cleavage is insufficient or lacking as is the case in thrombotic thrombocytopenic purpura (TTP). This evidence concerns the gene ADAMTS13 and thrombotic thrombocytopenic purpura.