von Willebrand factor proteolysis is deficient in classic, but not in bone marrow transplantation-associated, thrombotic thrombocytopenic purpura - van der Plas, RM; Schiphorst, ME; Huizinga, EG; Hene, RJ; Verdonck, LF; Sixma, JJ; Fijnheer, R (Blood, 1999)