ADAMTS13 and thrombotic thrombocytopenic purpura: Either autoantibodies against ADAMTS13 or causative ADAMTS13 mutations in a homozygous or compound heterozygous state cause severe ADAMTS13 depletion in patients with TTP, which can be classified into immune-mediated TTP (iTTP) [9,10] or congenital TTP (cTTP) [11,12], also known as Upshaw–Schulman syndrome (USS), respectively.