A new tool to further explore the role of ADAMTS‐13 in health and disease

Abstract

See also Feys HB, Liu F, Dong N, Pareyn I, Vauterin S, Vandeputte N, Noppe W, Ruan C, Deckmyn H, Vanhoorelbeke K. ADAMTS-13 plasma level determination uncovers antigen absence in acquired thrombotic thrombocytopenic purpura and ethnic differences. This issue, pp 955-62.In 1996, a hitherto unrecognized protease was isolated from human plasma [1,2] that cleaved multimeric von Willebrand factor (VWF) in vitro to cleavage fragments previously reported to be generated in vivo [3]. Shortly after its discovery this VWFcleaving protease activity was found to be severely deficient in many patients diagnosed with acute idiopathic thrombotic thrombocytopenic purpura (TTP) [4][5][6], most often because of inhibitory IgG autoantibodies in acute acquired TTP [5][6][7], but sometimes also in siblings with an obviously hereditary form of TTP without inhibiting autoantibodies [4,5], a condition previously denoted as Upshaw-Schulman syndrome [8,9].In 2001, the VWF-cleaving protease was purified from human plasma to homogeneity allowing partial amino acid sequencing [10][11][12] and identification of the enzyme as a member of the ADAMTS (a disintegrin-like and metalloprotease with thrombospondin type 1-motifs) family of metalloproteases, denoted as ADAMTS-13 [13]. Independently, genome-wide linkage analysis in pedigrees affected by hereditary TTP identified the same gene and several different ADAMTS-13 mutations were reported: double heterozygous or homozygous mutations were putatively responsible for severely deficient ADAMTS-13 activity in affected patients; heterozygous carriers of mutations were asymptomatic and showed about 50% of normal VWF-cleaving protease activity [14].Even though functionally active recombinant ADAMTS-13 has been expressed in transfected mammalian cells already in 2002 [15], and many diagnostic studies on VWF-cleaving protease activity and functionally inhibiting autoantibodies in patients with TTP, other thrombotic microangiopathies and other disorders have been reported [for review, see 16-18], assays of ADAMTS-13 activity in human plasma have been subject to ongoing controversy. Several ADAMTS-13 activity assays, based on the degradation of purified or recombinant multimeric VWF by patient plasma and analyzing its multimeric pattern [1,5] Two multicenter studies [20,21] on several of these activity assays have been performed and generally have shown acceptable agreement concerning the detection of severe ADAMTS-13 functional deficiency ( < 5% of normal plasma activity); however, there was less concordance of the results on plasma samples with mildly decreased or normal ADAMTS-13 activity. Moreover, some assays proved to be clearly unreliable for diagnostic purposes [21]. A recently developed functional assay using a truncated 73-amino acid VWF peptide encompassing the 1605 Y-1606 M cleavage site and labeled with a fluorescent and quencher group on both sites of the cleavage site, respectively, allows for rapid activity measurement of ADAMTS-13 by fluorescence resonance energy transfer and may greatly...

Thrombotic thrombocytopenic purpura in childhood: An uncommon but life‐threatening cause of thrombocytopenia

“…In general, the ADAMTS‐13 activity assays rely on degradation of purified or recombinant multimeric VWF by patient plasma. There is general agreement across assays that severe ADAMTS‐13 functional deficiency is defined as <5% of normal plasma activity 13 . However, the role of ADAMTS‐13 measurement for establishing the diagnosis of TTP or predicting the clinical course remains uncertain, especially in patients with milder reductions or normal levels of ADAMTS‐13 7,9 .…”