Subsequently, the classification evolved toward a molecular basis of the disease (68): a disintegrin and metalloprotease with thrombospondin type one repeats, member 13 (ADAMTS13) deficiency is associated with thrombotic thrombocytopenic purpura; and HUS is classified as typical or atypical depending on whether shiga toxin is present or absent (HUS and aHUS, respectively). This evidence concerns the gene ADAMTS13 and thrombotic thrombocytopenic purpura.