ADAMTS13 and thrombotic thrombocytopenic purpura: D+HUS is caused by the action of Stx on multiple cell types in the kidney whereas D-HUS (atypical HUS) is caused by dysfunctional complement regulatory proteins, and TTP is initiated by deficient ADAMTS13 protease activity for degradation of platelet-activating ultra large von Willebrand factor (vWf) multimers.