ADAMTS13 and thrombotic thrombocytopenic purpura: Two major variants of TMA are hemolytic uremic syndrome (HUS) caused by Shiga toxin and thrombotic thrombocytopenic purpura (TTP) associated with decreased activity of a disintegrin-like and metalloproteinase with thrombospondin type 1 motifs member 13 (ADAMTS13]).