TTP is a life-threatening, multisystem disease caused by a deficiency in the metalloprotease ADAMTS-13. It is characterized by thrombocytopenia, microangiopathic hemolytic anemia, fever, neurologic changes, and renal abnormalities. Normally, ultra-large von Willebrand factor (UL-VWF), which is secreted from endothelial cells, is converted to a less polymerized form by ADAMTS-13. If this protease is deficient, UL-VWF accumulate in the circulation, and under high fluid shear spontaneously agglutinates unactivated platelets and forms thrombi which are deposited in the microcirculation, producing the characteristic features of TTP. Idiopathic TTP appears to be caused by autoantibodies against a ADAMTS-13. The presence of IgG autoantibodies against the protease distinguishes TTP purpura from related syndromes, including the hemolytic-uremic syndrome. Congenital TTP has been described. TTP occurs at a rate of 3.7 per year per million, and the mortality rate for promptly treated cases ranges from 10 to 20 percent. Many drugs have been associated with the syndrome.
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