ADAMTS13 and thrombotic thrombocytopenic purpura: TTP is caused by the severe plasma deficiency of the von Willebrand factor (VWF) cleaving protease, i.e., the disintegrin and metalloproteinase with a thrombospondin type 1 motif member 13 ADAMTS13, caused in most cases by neutralizing autoantibodies (acquired immune-mediated TTP).