A severe ADAMTS13 deficiency (defined as protease activity below 10% of normal or 10 U/dL), due to mutations within ADAMTS13 gene or specific anti-ADAMTS13 auto-antibodies, induces congenital TTP or immune-mediated TTP (iTTP), respectively [3,4,5,6]. This evidence concerns the gene ADAMTS13 and thrombotic thrombocytopenic purpura.