Exploration d'ADAMTS13 dans le purpura thrombotique thrombocytopénique

ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13) is the specific von Willebrand factor (VWF)-cleaving protease. Thrombotic thrombocytopenic purpura (TTP) is an uncommon thrombotic microangiopathy (TMA), related to a severe ADAMTS13 deficiency (activity < 10%). ADAMTS13 deficiency is either inherited (ADAMTS13 gene mutations), or acquired (anti-ADAMTS13 autoantibodies, mainly). A severe functional ADAMTS13 deficiency causes the blood accumulation of platelet hyperadhesive ultralarge VWF multimers, leading to the formation of platelet-rich microthrombi within small arterioles. These microthrombi are responsible for microangiopathic hemolytic anemia and thrombocytopenia, sometimes associated to widespread microvascular ischemia. Biological investigations should be performed when TMA is suspected (hemoglobin levels, platelet count, blood smear, parameters for hemolysis, electrolyte pattern, bacteriology, virology, β-hCG). Screening for ADAMTS13 activity is the first assay to be performed for ADAMTS13 investigation. Subsequent investigations are aimed to document ADAMTS13 severe deficiency: anti-ADAMTS13 IgGs titration potentially completed by the search for an ADAMTS13 circulating inhibitor. When inherited TTP (Upshaw Schulman-syndrome) is suspected, ADAMTS13 antigen and ADAMTS13 gene sequencing should be performed.