VWF and thrombotic microangiopathy: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a specific form of thrombotic microangiopathy caused by a severe antibody-mediated deficiency of to adisintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13), a plasma enzyme responsible for the physiological cleavage of von Willebrand factor (VWF) (1).