Hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are thrombotic microangiopathies (TMAs) manifesting with thrombocytopenia and microangiopathic hemolytic anemia. TMA have either an acquired or a genetic origin. The most common form of TMA is Shigatoxin-associated HUS, which is caused by certain strains of bacteria that produce exotoxins, the Shiga-like toxins causing endothelial damage. This form has generally a good outcome with supportive therapy. Immune-mediated HUS and TTP are caused by the formation of autoantibodies against complement factor H or ADAMTS-13, respectively. These forms benefit from plasma exchange combined with immunosuppressive treatments. Treatment of forms secondary to systemic diseases rests on specific treatments of the underlying condition. Genetic predisposition to HUS is determined by mutations in genes encoding complement regulatory proteins. The outcome is poor. Some forms respond to plasma treatment. Genetic deficiency of ADAMTS13 is associated with congenital TTP. This form benefits from plasma therapy.
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