Thrombotic thrombocytopenic purpura and the hemolytic-uremic syndrome

Large and unusually large von Willebrand factor (vWf) multimers may be resp onsible for systemic platelet aggregation in thrombotic thrombocytopenic pu rpura (TTP). This possibility is supported by studies that show deficient v Wf-cleaving metalloproteinase and increased platelet-vWf binding during TTP episodes. In acute idiopathic TTP, decreased vWf metalloproteinase is the result of autoantibodies against the enzyme. in familial and acquired hemol ytic-uremic syndrome, vWf-cleaving metalloproteinase activity is normal. A deficiency or defect in factor H, which normally dampens the activation of C3 via the alternative complement pathway, has been seen in some patients w ith familial hemolytic-uremic syndrome. Ticlopidine therapy is an important risk factor for TTP. Curr Opin Pediatr 2000, 12:23-28 (C) 1000 Lippincott Williams & Wilkins, Inc.