ADAMTS13 and thrombotic thrombocytopenic purpura: Since the reports of absolute ADAMTS13 deficiency (von Willebrand factor-cleaving metalloprotease) in TTP caused by autoimmune antibody to ADAMTS13 in 1998 by Tsai [6] and Furlan [7], TTP is now recognized as a distinct disorder with absence of detectable levels of ADAMTS13 activity as the defining feature of TTP [8].