ADAMTS13 and thrombotic thrombocytopenic purpura: Thrombosis in TTP is initiated when haemostatically-active ultralarge VWF multimers accumulate in the circulation because of a relative or absolute deficiency of the cleaving protease, ADAMTS-13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13) [5].