VWF and thrombotic thrombocytopenic purpura: Recent observations have documented that a deficiency of a Von Willebrand factor (VWF)-cleaving protease, termed ADAMTS13 ('a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13'), that normally cleaves hyper-reactive unusually large VWF multimers into smaller and less adhesive VWF forms, may be responsible for many cases of TTP [2].