Thrombotic microangiopathies: towards a pathophysiology-based classification.
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.
Coppo
Paul
P
Service d'Hématologie et de Thérapie Cellulaire, Hôpital Saint-Antoine, 184 rue du Fbg St Antoine 75012 Paris, France. paulcoppo@aol.com
Veyradier
Agnès
A
D051722:ADAM Proteins / Q000172:deficiency / Q000235:genetics; D000071120:ADAMTS13 Protein; D000818:Animals; D001323:Autoantibodies / Q000378:metabolism; D015551:Autoimmunity; D016503:Drug Delivery Systems; D006463:Hemolytic-Uremic Syndrome / Q000145:classification / Q000503:physiopathology* / Q000628:therapy; D006801:Humans; D008833:Microcirculation; D010974:Platelet Aggregation; D011697:Purpura, Thrombotic Thrombocytopenic / Q000145:classification / Q000503:physiopathology* / Q000628:therapy; D012720:Severity of Illness Index; D014841:von Willebrand Factor / Q000378:metabolism
D001323:Autoantibodies; D014841:von Willebrand Factor; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human