ADAMTS13 and thrombotic thrombocytopenic purpura: ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) is a metalloproteinase that cleaves the polymers of vWF, and diminished activity of ADAMTS13 is the diagnostic hallmark of thrombotic thrombocytopenic purpura.