ADAMTS13 and thrombotic thrombocytopenic purpura: Although congenital TTP cases exist, most sporadic cases of TTP appear to be associated with severe deficiency of ADAMTS13 activity due to autoantibodies against it.1 After endothelial damage, huge amounts of vWF stored as ultra-large multimers (ULMM) in Weibel Pallade bodies, is released in the circulation.