ADAMTS13 and thrombotic thrombocytopenic purpura: The first episode of TTP mostly occurs in adulthood, and approximately 90% of adult cases with TTP are acquired autoimmune disorders (mainly idiopathic) resulting in the production of circulating autoantibodies directed against ADAMTS13, a metalloprotease that cleaves the endothelial cell-derived ultra-large von Willebrand factor (vWF) multimers (2–4).