VWF and thrombotic thrombocytopenic purpura: TMA is a causally heterogeneous syndrome related to several conditions including thrombotic thrombocytopenic purpura (TTP) and haemolytic-uraemic syndrome (HUS), which are primarily caused by a functional deficiency of ADAMTS 13 (an enzyme involved in the degradation of Von Willebrand Factor) activity and Shiga toxin or complement dysregulation, respectively.