VWF and thrombotic thrombocytopenic purpura: Typical HUS is often caused by Shiga toxin-producing Escherichia coli type 0157:H7.[3] Thrombotic thrombocytopenic purpura (TTP) is also a similar disease of thrombotic microangiopathy, characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and microthrombi in several organs (eg, the heart, central nervous system, and, to a lesser degree, the kidneys).[4] Serum ADAMTS13 is a zinc-containing metalloprotease enzyme that cleaves von Willebrand factor, a large protein involved in blood clotting.