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Thrombotic Microangiopathies: Towards a Pathophysiology-Based Classification

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Abstract:

Thrombotic microangiopathies (TMA) encompass various diseases characterized by a microangiopathic hemolytic anemia, platelet clumping, and organ failure of variable severity. Thrombotic thrombocytopenic purpura (TTP) is a particularly severe form of TMA characterized by systemic organ failure which results from a severe defect in ADAMTS13, a plasma enzyme specifically involved in the cleavage of highly hemostatic unusually large (UL) von Willebrand factor (VWF) multimers into smaller and less adhesive VWF forms. Failure to degrade these UL-VWF multimers leads to excessive platelet aggregates and capillary occlusion. ADAMTS13 deficiency results from bi-allelic mutations in hereditary TTP, whereas in acquired forms it results from autoantibodies that alter the protein function. Patients with acquired idiopathic TTP have a trend to develop autoimmunity, since a clinical context of autoimmunity may be found in 30 p. cent of cases. Moreover, the remarkable efficiency of monoclonal antibodies directed against CD20 antigen of B lymphocytes in refractory or chronic relapsing forms provides an additional indirect argument to consider acquired TTP as an autoimmune disease.

Hemolytic uremic syndrome (HUS) is characterized prominently by a renal failure. In most cases, HUS is caused by entero- hemorrhagic Escherichia coli (diarrhea-positive HUS). Diarrhea-negative HUS, termed atypical HUS, was associated with a dysfunction in complement pathway involving mutations in factor H, factor I, CD46/MCP, factor B and C3 components.

The major improvement in our understanding of TMA pathophysiology allows now a more accurate molecular classification of TMA syndromes, which opens fascinating perspectives of targeted therapies in the forthcoming years.

Keywords: ADAMTS13; Thrombotic thrombocytopenic purpura; autoimmune disease; complement; hemolytic uremic syndrome; thrombocytopenia; thrombotic microangiopathies

Document Type: Research Article

Publication date: March 1, 2009

More about this publication?
  • Cardiovascular & Hematological Disorders - Drug Targets aims to cover all the latest and outstanding developments on the medicinal chemistry, pharmacology, molecular biology, genomics and biochemistry of contemporary molecular targets involved in cardiovascular and hematological disorders e.g. disease specific proteins, receptors, enzymes, genes. Each issue of the journal will contain a series of timely in-depth reviews written by leaders in the field covering a range of current topics on drug targets involved in cardiovascular and hematological disorders. As the discovery, identification, characterization and validation of novel human drug targets for cardiovascular and hematological drug discovery continues to grow; this journal will be essential reading for all pharmaceutical scientists involved in drug discovery and development.
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