While patients with congenital TTP and acquired immune TTP attributed to low ADAMTS-13 activity demonstrate a good response to plasma infusion or plasma exchange (PEX), other clinical forms of TMA occur in the absence of severe ADAMTS-13 deficiency, and this may be the reason why patients with the other clinical forms of TTP do not respond to plasma therapy.26 This evidence concerns the gene ADAMTS13 and thrombotic thrombocytopenic purpura.