Thrombotic thrombocytopenic purpura, hereditary or acquired, is secondary to deficiency of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), which causes the formation of large von Willebrand factor (vWF) multimers and platelet aggregation. This evidence concerns the gene VWF and thrombotic thrombocytopenic purpura.