ADAMTS13 and thrombotic thrombocytopenic purpura: Currently, a severe deficiency in ADAMTS13 : AC, which results either from genetic mutations in the ADAMTS13 gene (Upshaw-Schulman syndrome, (USS)) [5–8] or acquired autoantibodies against ADAMTS13 [9, 10], is thought to be a specific feature of thrombotic thrombocytopenic purpura (TTP) [5–12].