TTP is associated with low or undetectable ADAMTS13 activity (usually <10%), which may be related to a rare genetic defect in the ADAMTS13 gene (Upshaw–Schulman syndrome) or is, in most cases, an autoimmune disease associated with auto-antibodies neutralizing the enzymatic functions of ADAMTS13 (6). This evidence concerns the gene ADAMTS13 and thrombotic thrombocytopenic purpura.