The importance of ADAMTS13 activity level in TTP is controversial.18,19 Coppo et al. showed that 71% of patients clinically diagnosed with TTP had severe ADAMTS13 deficiency.20 In Oklahoma registry data of 301 patients 13% of all patients, and 33% of patients with idiopathic TTP-HUS, had very severe ADAMTS-13 deficiency (<5% activity).12 The presenting features and clinical outcomes of patients with severe ADAMTS-13 deficiency were heterogeneous and not distinct.12 This evidence concerns the gene ADAMTS13 and thrombotic thrombocytopenic purpura.