ADAMTS13 and thrombotic thrombocytopenic purpura: In contrast to thrombotic thrombocytopenic purpura (TTP), which is defined as a severe deficiency of plasma ADAMTS13 (a disintegrin-like metalloproteinase with thrombospondin motif type 1 member 13) activity secondary to absent or dysfunctional protein production due to mutations in the ADAMTS13 gene (ie, congenital TTP) or autoantibody-mediated clearance and/or inhibition (ie, immune-mediated TTP) [7], most cases of DI-TMA are not associated with severe ADAMTS13 deficiency/inhibition.