ADAMTS13 and thrombotic thrombocytopenic purpura: Deviation from normal levels and activity in each, in the form of increased VWF or decreased ADAMTS13 activity, may be associated with an increased risk of thrombosis, exemplified by thrombotic thrombocytopenic purpura (TTP) [61,62] and thrombosis associated with cancer [63], systemic lupus erythematosus, and systemic sclerosis [64,65,66].