Deficient activity of von Willebrand factor-cleaving protease in patients with Upshaw-Schulman syndrome

We identified unusually large von Willebrand factor (vWF) multimers caused by deficient activity of OAT-cleaving protease in 2 patients with Upshaw-Sc hulman syndrome. The autoantibodies that inhibited the protease activity we re not detected in the plasma of either patient. Periodic fresh-frozen plas ma transfusion was effective for management of the hemolysis and thrombocyt openia. We detected enriched enzyme activity in a particular plasma fractio n, although molecular cloning of this specific protease is needed to determ ine a more detailed pathogenesis and to develop new therapeutic approaches. (C) 2001 The Japanese Society of Hematology.