ADAMTS13 and thrombotic thrombocytopenic purpura: Prospective studies combing gene expression profiling and immunophenotyping are required to determine whether the relapse-associated transcriptional signatures and altered expression of NK and T lymphocyte cell surface markers reported here signify risk or consequence of relapse in ADAMTS13-deficient TTP, and we have initiated collection of samples from newly diagnosed, ADAMTS13-deficient TTP patients for this purpose.