VWF and thrombotic thrombocytopenic purpura: Thrombotic Thrombocytopenic Purpura (TTP) is an acute, life-threatening thrombotic microangiopathy caused by deficient activity of the von Willebrand factor (VWF) cleaving protease ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, 13th member).