Classical TTP results from a deficiency of a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity, leading to an accumulation of multimeric, prothrombotic von Willebrand factor (vWF) that drives intravascular thrombosis by the agglutination of circulating platelets under high shear stress [9]. The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.