SEARCH

SEARCH BY CITATION

Keywords:

  • ADAMTS-13;
  • thrombotic microangiopathy;
  • thrombotic thrombocytopenic purpura;
  • von Willebrand factor-cleaving protease

Abstract

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

Summary.  This overview summarizes the history of thrombotic thrombocytopenic purpura (TTP) from its initial recognition in 1924 as a most often fatal disease to the discovery in 1997 of ADAMTS-13 deficiency as a major risk factor for acute disease manifestation. The cloning of the metalloprotease, ADAMTS-13, an essential regulator of the extremely adhesive unusually large von Willebrand factor (VWF) multimers secreted by endothelial cells, as well as ADAMTS-13 structure and function are reviewed. The complex, initially devised assays for ADAMTS-13 activity and the possible limitations of static in vitro assays are described. A new, simple assay using a recombinant 73-amino acid VWF peptide as substrate will hopefully be useful. Hereditary TTP caused by homozygous or double heterozygous ADAMTS-13 mutations and the nature of the mutations so far identified are discussed. Recognition of this condition by clinicians is of utmost importance, because it can be easily treated and – if untreated – frequently results in death. Acquired TTP is often but not always associated with severe, autoantibody-mediated ADAMTS-13 deficiency. The pathogenesis of cases without severe deficiency of the VWF-cleaving protease remains unknown, affected patients cannot be distinguished clinically from those with severely decreased ADAMTS-13 activity. Survivors of acute TTP, especially those with autoantibody-induced ADAMTS-13 deficiency, are at a high risk for relapse, as are patients with hereditary TTP. Patients with thrombotic microangiopathies (TMA) associated with hematopoietic stem cell transplantation, neo-plasia and several drugs, usually have normal or only moderately reduced ADAMTS-13 activity, with the exception of ticlopidine-induced TMA. Diarrhea-positive-hemolytic uremic syndrome (D+ HUS), mainly occurring in children is due to enterohemorrhagic Escherichia coli infection, and cases with atypical, D− HUS may be associated with factor H abnormalities. Treatment of acquired idiopathic TTP involves plasma exchange with fresh frozen plasma (FFP), and probably immunosuppression with corticosteroids is indicated. We believe that, at present, patients without severe acquired ADAMTS-13 deficiency should be treated with plasma exchange as well, until better strategies become available. Constitutional TTP can be treated by simple FFP infusion that rapidly reverses acute disease and – given prophylactically every 2–3 weeks – prevents relapses. There remains a large research agenda to improve diagnosis of TMA, gain further insight into the pathophysiology of the various TMA and to improve and possibly tailor the management of affected patients.


Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

In 1924, Dr Eli Moschcowitz described a 16-year-old girl who died within 2 weeks after the abrupt onset and progression of petechial bleeding, pallor, fever, paralysis, hematuria and coma [1]. Disseminated microvascular ‘hyaline’ thrombi were detected at autopsy, and these widespread thrombi in arterioles and capillaries, later found to be largely composed of platelets, remain the pathologic hallmark of Moschcowitz’ disease or thrombotic thrombocytopenic purpura (TTP) today [2,3]. Moschcowitz suspected that a powerful agglutinative and hemolytic poison was responsible for this disease [4].

In a landmark paper of 1966, Amorosi and Ultmann [5] reviewed some 250 reported patients with TTP, added 16 new cases and established a pentad of clinical and laboratory features still considered to be the key diagnostic criteria: microangiopathic hemolytic anemia with fragmented erythrocytes (schistocytes) in the peripheral blood smear (Fig. 1), thrombocytopenia, (often fluctuating) neurologic signs and symptoms, renal dysfunction and fever. Nowadays, it is generally believed that intravascular platelet clumping under high shear stress in the microcirculation results in thrombocytopenia, ischemic neurologic, renal and other organ dysfunction and intravascular fragmentation of red blood cells in the partially occluded arterioles and capillaries.

image

Figure 1. Peripheral blood smear from a patient with acute TTP showing many fragmented erythrocytes (schistocytes) (arrows) and severe thrombocytopenia.

Download figure to PowerPoint

Hemolytic uremic syndrome (HUS), reported in 1955 by Gasser et al. [6] in five children, is a disease clinically very similar to TTP. In routine clinical practice, TTP was often diagnosed in adult patients with predominant neurologic symptoms whereas a diagnosis of HUS was often made in children with predominant renal failure. Nevertheless, this distinction was not universally accepted and some authors adopted the term ‘TTP/HUS’ presuming a similar pathomechanism with variable organ tropism. Whereas many cases of TTP occur in previously healthy persons, childhood HUS is often associated with preceding hemorrhagic colitis caused by verocytotoxin-producing Escherichia coli O157:H7 infection, and this illness is nowadays labelled typical (diarrhea-positive or D+) HUS [7].

In addition, thrombotic microangiopathies (TMA) associated with pregnancy, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), disseminated cancer, anticancer agents such as mitomycin C, hematopoietic stem cell transplantation, various drugs such as cyclosporine A, ticlopidine, clopidogrel, quinine and others, and human immunodeficiency virus infection have been observed and variably referred to as TTP, HUS, TTP-HUS, TTP-like disease or secondary TTP (for review see Refs [8,9]).

Numerous hypotheses on the etiology and pathogenesis of idiopathic TTP have been put forward over the years (for reviews, see Refs [8,10–12]). Among others, endothelial injury, e.g. by oxidative stress, decreased prostacyclin production, reduced fibrinolytic capacity of the vessel wall, anti-endothelial cell autoantibodies and specifically antibodies toward glycoprotein IV (CD36) [13,14] that is located on microvascular endothelial cells and platelets, and the capacity of TTP plasma to induce apoptosis of microvascular endothelial cells [15] have been proposed as pathogenetic factors. Moreover, a 37-kDa protein [16], and a 59-kDa protein or a calcium-dependent cysteine protease (calpain) [17,18] were identified in serum or plasma from patients with acute TTP and suggested to be responsible for in vivo platelet aggregation. In 1982, Moake et al. [19] reported the presence of unusually large von Willebrand factor (ULVWF) multimers in plasma of four patients with a chronic relapsing course of TTP during remission. They suspected that these highly polymeric VWF multimers, similar in size to those found in endothelial cell-culture supernatant, were responsible for in vivo platelet clumping in the microvasculature. Moake et al. [19] hypothesized that the lack of a ‘depolymerase’ was responsible for the persistence of these ULVWF multimers in their patients.

In 1996, Furlan et al. [20] and Tsai [21] simultaneously isolated a hitherto unknown plasma protease that specifically cleaved VWF multimers at the peptide bond Tyr842–Met843 of the mature VWF subunit (Tyr1605–Met1606 in amino acid numbering including the VWF propeptide), the peptide bond previously shown to be cleaved during physiologic processing of VWF in vivo [22]. One year later, four patients, including two brothers, with a chronic relapsing TTP and showing ULVWF multimers in their plasma during remission, were found to completely lack any VWF-cleaving protease (VWF-cp) activity [23]. In 1998, we observed another patient with a severe course of TTP lacking any VWF-cp activity whose plasma contained an IgG autoantibody inhibiting VWF-cp activity in normal plasma [24]. The inhibitor disappeared transiently after plasma exchange and replacement of fresh frozen plasma (FFP), corticosteroid and vincristine treatment and this was paralleled by normalization of VWF-cp and clinical remission. Reappearance of the IgG inhibitor with disappearance of protease activity preceded the first clinical relapse and only splenectomy performed 1 year after disease onset led to persistent clinical remission, absence of inhibitor and normal VWF-cp activity [24]. Two separate retrospective studies on large cohorts of patients with TTP and HUS appearing in the same issue of the New England Journal of Medicine [25,26] demonstrated that the majority of patients with acute sporadic TTP had a severe deficiency of VWF-cp, most of them with inhibiting autoantibodies that disappeared in all [26] or some [25] patients in remission. Six familial cases (three pairs of siblings) had a complete protease deficiency without inhibitors [25] and 23 patients with a diagnosis of HUS had normal or subnormal VWF-cleaving protease activity [25].

Acute TTP was mostly fatal until the empirical introduction of plasma therapy in the 1970s [27]. In a prospective randomized study, the Canadian Apheresis Study Group [28] showed the superiority of plasma exchange and FFP replacement over FFP infusion. Using plasmapheresis and FFP replacement, some 80% of the patients survive the acute TTP episode [9]. The number of plasma exchange procedures and hence the treatment duration varies greatly and many patients relapse during follow-up [29–31]. Often, additional treatment, such as corticosteroids [32], vincristine, other immunosuppressive medication and/or splenectomy is given, especially in refractory or relapsing cases (for reviews, see Refs [8–10,33]). These largely empirical treatments seemed to be pathophysiologically supported by the discovery that many patients with acute TTP had an autoantibody-mediated deficiency of the specific VWF-cp: plasma exchange and corticosteroids would probably remove circulating autoantibodies and suppress formation of VWF-cp inhibitors, respectively, and FFP replacement would supply the lacking protease.

The very careful clinical observation during long-term follow-up of a patient with frequently recurring severe thrombocytopenia and microangiopathic hemolytic anemia since childhood, repeatedly showing a prompt response within a few hours to simple plasma infusion, led Upshaw [34] to conclude that his and Schulman's similar patient [35] were congenitally deficient in a plasma factor protecting from hemolysis and thrombocytopenia.

For reviews giving personal accounts of the discovery of ULVWF in TTP, VWF-cleaving protease and its deficiency in TTP the reader is referred to three interesting recent historical sketches by Furlan [36], Tsai [37] and Moake [38].

Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

von Willebrand factor-cleaving protease was purified to homogeneity and subjected to N-terminal amino acid sequence analysis [39–41]. This allowed to identify VWF-cp as a new member of the ADAMTS (a disintegrin and metalloprotease with thrombospondin type 1 motifs) family of metalloproteases, denoted as ADAMTS-13 [42] and to locate the gene to chromosome 9q34.

Simultaneously, Levy et al. [43], performing a genome-wide linkage analysis in patients with hereditary TTP displaying severe VWF-cp deficiency and their family members detected the same gene, ADAMTS-13. They identified several different mutations as being presumably responsible for the severely deficient protease activity and hereditary TTP in homozygous or double heterozygous carriers of mutated alleles, whereas family members with a heterozygous mutation had about 50% of protease activity and were clinically asymptomatic [43].

The ADAMTS-13 gene spans approximately 37 kb, contains 29 exons and encodes a precursor polypeptide composed of 1427 amino acid residues [42,43] (Fig. 2). The polypeptide consists of a signal peptide, a short propeptide with a C-terminal furin cleavage site, a catalytic domain with a typical reprolysin-type active site sequence (HEXGHXXGXXHD) coordinating a Zn2+ ion and a Ca2+ binding site motif (E83, D173, C281, D284), a disintegrin domain, a thrombospondin type 1 domain, a cysteine-rich domain, a spacer domain, seven additional thrombosponding type 1 motifs and two CUB domains (Fig. 2).

image

Figure 2. Gene structure and protein domains of ADAMTS-13. The ADAMTS-13 gene consists of 29 exons (upper panel), encoding the ADAMTS-13 protein (middle panel), consisting of a signal peptide (S), a propeptide (P), a metalloprotease domain, a disintegrin domain (Dis), 8 thrombospondin type 1 domains (1–8), a cysteine-rich (Cys) and spacer domain, and two CUB domains. Mutations of ADAMTS-13 identified in patients with hereditary TTP and severe functional ADAMTS-13 deficiency (lower panel). Splice site ([UPWARDS ARROW]), nonsense (bsl00084), missense (bsl00079) and frameshift (bsl00063) mutations (known as of January 2005).

Download figure to PowerPoint

The calculated molecular mass is 145 kDa, the protein isolated from human plasma has an apparent mass of 180 kDa [39] and is heavily glycosylated [44]. Northern blotting of various tissues revealed a 4.7-kb mRNA transcript in liver tissue [41,42] and in situ hybridization showed that ADAMTS-13 was mainly expressed in the perisinusoidal cells of the liver [45]. Low expression of ADAMTS-13 mRNA was found in several other organs [46] and mRNA was recently detected in platelets [47]. In addition, a shorter 2.4-kb mRNA transcript was isolated from placenta, skeletal muscle and tumor cell lines [42].

Recombinant ADAMTS-13 has been transiently expressed in mammalian cell lines [46,48–50]. Secreted ADAMTS-13 has the propeptide cleaved off, is functionally active [46] and when added to congenitally ADAMTS-13-deficient plasma, it dose-dependently restored its VWF-cleaving protease activity [51].

ADAMTS-13 purified from normal plasma showed a series of bands with apparent Mr of 180, 170, 160 and 120 kDa [39], all having an identical N-terminal sequence, thus being obviously truncated at various distances from the C-terminus. Similar C-terminally truncated species have been found in supernatants but not in lysates of transiently transfected mammalian cell lines [44] suggesting that they resulted from proteolysis upon secretion.

Recombinant ADAMTS-13 recovered from conditioned medium of transfected cells is an active enzyme that does not need further activation. Regulation of VWF cleavage may be provided by the substrate VWF itself. In vivo, shear stress as observed in the microcirculation may be needed to make the cleavage site in the A2 domain of the VWF subunit accessible to ADAMTS-13 [21,52], whereas in vitro partial unfolding of the VWF substrate by guanidine-HCl [21] or urea and low ionic strength [20] similarly renders VWF accessible and cleavable by ADAMTS-13. rADAMTS-13 obtained from lysed transfected cells shows only minimal VWF-cleaving activity [46]. Whether this is due to the cell-lysing procedure, to incomplete glycosylation or to intracellular inhibitor(s) is not known. Recombinant as well as plasma derived ADAMTS-13 specifically cleave recombinant or plasma-derived VWF at Tyr1605–Met1606 [44,46], and rADAMTS-13 or plasma-derived ADAMTS-13 incubated with rVWF results in the generation of the typical triplet pattern as seen in plasma VWF multimers [44,53]. Besides VWF, no other protein substrate of ADAMTS-13 has been identified [20,50]. Metal ion chelators, such as ethylenediaminetetraacetic acid (EDTA), inhibit ADAMTS-13 activity [20,21] and very recently, free hemoglobin was shown to inhibit plasma ADAMTS-13 activity [54].

Zheng et al. [50] and Soejima et al. [49] constructed rADAMTS-13 deletion mutants by progressively truncating the C-terminal region. Truncation of the CUB domains and the thrombospondin type 1 repeats 2–8 led to the slight loss of VWF-cp activity in a static in vitro system. Activity was (almost) completely lost by further truncation of the spacer domain. On the contrary, it was shown that rADAMTS-13 synthesized in a furin-deficient cell line and secreted with the propeptide attached had normal VWF-cp activity [55]. In vivo, the thrombospondin type 1 repeats 2–8 and the CUB domains may still be important for proper interaction with VWF [56].

Dong et al. [57] showed that cultured endothelial cells, upon stimulation with histamine, secreted extremely long VWF multimer strands that remained attached to the endothelial cells, at least partly in a P-selectin-dependent manner [58]. If these stimulated endothelial cells were perfused with platelets in buffer, platelets attached to the ultra-large VWF and formed long ‘beads-on-a-string’ structures. Further perfusion with normal plasma or partially purified ADAMTS-13 rapidly detached the adhering platelets by cleaving endothelium-anchored ULVWF. Perfusion with plasma from patients with severe constitutional or acquired ADAMTS-13 deficiency, however, was unable to cleave VWF and to detach the platelets [57]. Further studies suggested that ADAMTS-13 binds to the A1 and A3 domains of VWF [56] enabling the protease to cleave the peptide bond in the near A2 domain becoming accessible under tensile forces. These findings suggest that ADAMTS-13 regulates the size of VWF multimers by its capacity to cleave VWF upon its secretion in the form of ULVWF on the endothelial surface [59].

ADAMTS-13 assays

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

Several assays for assessing ADAMTS-13 activity have been developed (for reviews, see Refs [60,61]). They are based on the degradation of purified, plasma-derived or recombinant VWF multimers by patient plasma and (i) measuring the disappearance of larger VWF multimers using sodium dodecyl sulfate (SDS)-agarose gel electrophoresis and immunoblotting [20,25], (ii) assaying the generation of disulfide-linked homodimers (Mr 350 kDa) of C-terminal VWF proteolytic fragments [21,26], (iii) quantitating the residual collagen-binding activity [62] or (iv) quantitating the ristocetin cofactor activity [63] of degraded VWF. A two-site immunoradiometric assay using monoclonal antibodies against C- and N-terminal VWF epitopes has also been reported [64]. In all these assays, the cleavage site at Tyr1605–Met1606 in VWF multimers is made accessible to ADAMTS-13 by partial VWF unfolding using either guanidine-HCl [21] or 1.5 m urea and low ionic strength [20]; and barium [20] or calcium ions [21] are used to ‘activate’ ADAMTS-13.

Because of major vigorous debates about the suitability of these various methods, we initiated a multicenter comparison involving several laboratories performing different assay techniques on identical aliquots of 30 plasma samples with varying ADAMTS-13 activity levels [65]. This evaluation showed a generally good agreement between the five participating laboratories concerning detection of severe ADAMTS-13 deficiency (<5% of the activity in pooled normal plasma), whereby the convenient but very delicate collagen-binding assay yielded some erroneous results (two false-positive diagnoses of severe deficiency and one failure to detect a severe deficiency) and the interlaboratory agreement on samples with slightly reduced or normal activity values was less good [65]. A larger comparative exercise involving 10 expert laboratories and 11 methods [66] essentially confirmed and extended these results.

Inhibitors of ADAMTS-13 are measured with all reported methods by pre-incubating (heat-inactivated [67]) patient plasma with pooled normal plasma for 2 h and measuring the residual VWF-cleaving activity of normal plasma [65,67]. Our multicenter study showed good interlaboratory agreement for the detection of strong inhibitors (more than 1 BU mL−1), whereas there was considerable disagreement for low-titer inhibitors [65]. It is evident that this mixing technique allows only the detection of free IgG inhibitors in plasma that have not been bound to ADAMTS-13 and is – therefore – not very sensitive.

A probably more physiologic method for measuring ADAMTS-13 activity was proposed by Dong et al. [57,68]. Based on the earlier observations by Tsai et al. [52] that shear stress enhances the proteolysis of VWF, they assay the ability of plasma to detach platelets adhering to ULVWF strings on stimulated endothelial cell cultures using a parallel plate perfusion system [57]. This method has the conceptual advantage of testing not only the proteolytic activity of ADAMTS-13 but also its ability to attach to VWF and/or the endothelial cells under flow conditions which mirrors the physiologic function of ADAMTS-13 better than the mere cleavage of partially denatured VWF multimers under static conditions. Nevertheless, this assay is very complex and in the above-mentioned multicenter study [66] the reproducibility of this assay was not perfect: only seven of 10 replicate plasma samples with severe ADAMTS-13 deficiency were correctly identified, whereas three of 10 replicate samples with 40% ADAMTS-13 activity were judged to show a severe deficiency [66].

To improve static assays of ADAMTS-13 activity, recombinant VWF A1-A2-A3 [69] or rVWF A2 domain [70] have been proposed as substrates. Kokame et al. [71] expressed a series of recombinant VWF peptides containing the cleavage site 1605Tyr–1606Met and identified a peptide containing 73 amino acids from 1596Asp–1668Arg as the minimal substrate required for efficient cleavage by ADAMTS-13. Adding N- and C-terminal glutathione S-transferase and histidine tags, respectively, substrate purification and detection of substrate as well as cleavage product by SDS-polyacrylamide gel electrophoresis (PAGE) is greatly facilitated [71]. This GST-VWF73-H peptide allows sensitive measurement of plasma ADAMTS-13 activity of only 3% of normal plasma [71] and by introducing fluorescent probes on both sites of the cleavage site, a convenient fluorescence resonance energy transfer (FRET) assay has been established that will greatly facilitate and accelerate ADAMTS-13 activity measurement and provide an assay suitable for the routine laboratory [72].

In addition, methods for measuring ADAMTS-13 antigen (F. Scheiflinger unpubl. obs.) and for detecting autoantibodies directed against ADAMTS-13 [73] using enzyme-linked immunosorbent assays (ELISAs) have been developed. It is noteworthy that in at least one reported patient with acquired TTP and severe ADAMTS-13 deficiency, a high-titer IgG autoantibody toward ADAMTS-13 was found by ELISA, whereas functional assays did not reveal an inhibitor of VWF-cleaving protease in this plasma [73]. This suggests that in some cases non-inhibiting autoantibodies may result in severe ADAMTS-13 deficiency, e.g. by accelerating the clearance of the enzyme.

Hereditary TTP

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

In 1978, Upshaw [34] concluded that his patient, a young woman with recurring episodes of severe microangiopathic hemolytic anemia and thrombocytopenia was congenitally deficient in a plasma factor that protected from intravascular hemolysis and thrombocytopenia. This plasma factor was identified in 1997 as VWF-cleaving protease in two brothers with chronic relapsing TTP [23]. Since then, several cases of constitutional TTP because of severely deficient ADAMTS-13 activity have been reported [67,74–83]. Reviewing the clinical courses in 23 patients from 16 families with severe constitutional VWF-cleaving protease deficiency identified until 2001 in our laboratory revealed a striking age-dependent clustering of disease onset [11]: about half of the patients had their first bout of TTP between the neonatal period and 5 years of age, whereas the other half had disease onset in adulthood, between 20 and 41 years of age, and two male subjects diagnosed in the frame of a family investigation were still asymptomatic at age 37 and 44 years, respectively. Frequent relapses were noted in patients with early or late onset, once a first bout of TTP had occurred. The diagnosis of TTP was often greatly delayed and several siblings of affected patients had died [11]; we have recently reported a fatal outcome in an 8-year-old boy where the diagnosis of TTP was made only at autopsy [54]. Schneppenheim et al. [53] made similar clinical observations, several of their pediatric patients had been misdiagnosed as having atypical, Coombs-negative Evans’ syndrome or immune thrombocytopenic purpura. Some patients with severe constitutional VWF-cleaving protease deficiency had been clinically diagnosed as having HUS because of prominent renal failure [69,84]. In fact, the index patient (brother A1), completely lacking VWF-cleaving protease activity also showed transient severe renal failure at his first attack [23]. Other patients with severe hereditary protease deficiency suffer mainly from cerebrovascular ischemia [74], and others have mainly recurring hemolytic anemia and thrombocytopenia. It should also be noted that in earlier reports, published at a time when ADAMTS-13 was still unknown, TTP and HUS were described to coexist in siblings [85,86]. This stresses the fact that, on clinical grounds, TTP and HUS cannot be clearly separated [9].

In a landmark study, Levy et al. [43] identified 12 different mutations in the ADAMTS-13 gene accounting for 14 of 15 disease alleles in their families with hereditary TTP. This study convincingly related hereditary TTP to the ADAMTS-13 gene. As of January 2005, a total of 75 candidate mutations in patients with constitutional TTP have been described [43,48,51,53,54,87–101; J. A. Kremer Hovinga, B. Lamoule unpubl. data] (Fig. 2). Affected patients are double heterozygous or homozygous carriers of mutated alleles, the heterozygous parents being consistently asymptomatic. Only about one-third of the reported mutations have been expressed in mammalian cells [48,92–94,102]. Most of the mutated proteins are not secreted [48,92–94,102], others are secreted but show deficient VWF-cleaving activity [92,94].

So far, no correlation between genotype and phenotype, i.e. disease severity, organ tropism and age at disease onset is evident. Other disease-modifying genetic or environmental triggering factors may be needed to result in clinical disease. In this context, we became aware of two pairs of sisters from two families who suffered their first bout of hereditary TTP during pregnancy, whereas their protease-deficient brothers were asymptomatic at age >35 years [11]. It may be hypothesized that increased VWF synthesis during pregnancy, a known risk factor for TTP [103,104], may be such a triggering factor.

It is generally assumed that hereditary TTP is extremely rare. Nevertheless, we believe that this disease may have been greatly underestimated and misdiagnosed. A single nucleotide transition in the ADAMTS-13 gene leading to a Pro475Ser substitution has an allele frequency of approximately 5% in the Japanese population [48]. Expression of this mutant showed normal secretion of an obviously dysfunctional protease, the activity in a static assay being about 5% as compared with wild-type ADAMTS-13 [48]. Whether homozygous carriers of this mutation are at risk for TTP or whether the presumably quite low ADAMTS-13 activity level is completely asymptomatic has not yet been reported. A disease-associated mutation, however, a single nucleotide insertion in exon 29, 4143insA, was identified in four unrelated patients from Germany [53], in two brothers from Sweden [88] and one patient from Australia [94]. Another seven patients have been recently detected and preliminary haplotype analysis suggests a common founder mutation, possibly arising in an ancestor near the Baltic sea region [105]. Because several apparently not consanguineous patients with a homozygous 4143insA mutation have been identified, it is likely that many still undiagnosed homozygous carriers, either patients with undiagnosed constitutional TTP or high risk candidates to suffer from TTP, may exist.

It is of utmost importance that pediatricians, internists, nephrologists and hematologists be aware of hereditary TTP because efficient treatment and prophylactic measures are available (see below).

Acquired TTP

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

Patients with acute acquired TTP, like those with an acute bout of hereditary TTP, are usually severely ill, most of them are not suffering from a pre-existing underlying disease. Because of the high fatality rate in untreated patients [5,9], diagnosis is urgent, but may be difficult if the patient does not present the complete pentad of clinical and laboratory findings (see above). Schistocytic hemolysis and thrombocytopenia, not explained by another condition, may allow a tentative diagnosis even though these are not highly specific diagnostic criteria [9].

Following the reports in 1998, that 20 of 24 [25] and all of 37 [26] patients with acute acquired TTP had severe VWF-cleaving protease deficiency, most often associated with a circulating IgG inhibitor, autoantibody-mediated VWF-cleaving protease deficiency became a candidate laboratory criterion for the diagnosis of idiopathic TTP. Early critical reports suggested that VWF-cleaving protease deficiency was not specific for TTP, but was also found in disseminated intravascular coagulation (DIC) [106], in thrombocytopenic disorders different from TTP [107], in various acute inflammatory conditions, liver cirrhosis, uremia, during later stages of pregnancy, in newborns [108], and even in some healthy controls [107]. However, in these studies, VWF-cp activity was either not rigorously quantitated or was only moderately decreased. In a study on 68 patients with thrombocytopenia from various causes except TTP or HUS, 12 had values lower than 30%, but none <10%, in clear distinction to patients with acute TTP [109]. This suggests that a severely deficient activity of VWF-cp (<5% of normal) is specific for TTP. Nevertheless, subsequent cohort studies on patients diagnosed with acute (idiopathic) TTP showed that only about 33–100% had a severe protease deficiency [25,26,30,96,110–114] (Table 1). Obviously, not all patients clinically diagnosed with idiopathic TTP have a severe ADAMTS-13 deficiency as measured with current static protease activity assays.

Table 1.  Proportion of patients with severely deficient ADAMTS-13 activity (defined as <5% of normal in all studies, except <10% in [96]) in reported TTP case series
Author [Reference]Design of studySeverely deficient/totalSensitivity (%)
  1. Denominators refer to: *patients classified as having acute TTP; patients classified as having acute idiopathic TTP; patients with first attack or relapse of acute idiopathic TTP.

Furlan et al. 1998 [25]Retrospective, multicenter26/30*86
Tsai and Lian 1998 [26]Retrospective37/37*100
Veyradier et al. 2001 [110]Prospective, multicenter47/66*71
Mori et al. 2002 [111]Retrospective?12/18*66
Vesely et al. 2003 [30]Inception cohort, single center16/4833
Matsumoto et al. 2004 [113]Multicenter56/10852
Kremer Hovinga et al. 2004 [112]Multicenter56/9360
Zheng et al. 2004 [114]Single center, prospective16/2080
Peyvandi et al. 2004 [96]Multicenter48/100*48

An ADAMTS-13 epitope mapping of autoantibodies from 25 patients with acute TTP, severe or borderline to severe ADAMTS-13 deficiency and protease inhibiting autoantibodies showed that all 25 patients had antibodies reacting with the Cys-rich/spacer domain, 16 of 25 plasmas reacted with the CUB1+2 domains, 14 of 25 with the first thrombospondin type 1 domain, 14 of 25 with the catalytic/disintegrin/thrombospondin type 1/1 domains, seven of 25 with the thrombospondin type 1/2-8 domains, and five of 25 recognized the propeptide [115]. This shows that autoantibodies toward different antigenic regions are present in acute TTP. It seems likely that antibodies directed toward the Cys-rich/spacer domain account for the inhibition of ADAMTS-13 activity in static in vitro assays, but it is conceivable that antibodies toward other antigenic sites may impair the ADAMTS-13 interaction with endothelial cell-anchored ULVWF in vivo and that such antibodies may lead to clinical manifestions of TTP. Alternatively, other pathophysiologic mechanisms not involving ADAMTS-13-VWF interaction may lead to a syndrome clinically indistinguishable from that associated with severe acquired ADAMTS-13 deficiency.

In the Oklahoma TTP-HUS registry, 142 consecutive patients referred for plasma exchange treatment for suspected TTP-HUS between November 1996 and December 2001 had ADAMTS-13 assays performed on their stored admission serum samples [30]. Of 48 patients with idiopathic TTP, 16 had severe ADAMTS-13 deficiency, whereas 32 had moderately decreased, subnormal or normal protease values. The presenting clinical and laboratory findings were not different among the two groups, with the exception of acute renal failure being more frequent in those without severe deficiency (11/32) than in severely deficient patients (1/16). Clinical outcome, i.e. response to plasma exchange therapy, exacerbation, number of necessary plasma exchanges and death rate was not different among patients with and without lacking protease. Relapse rate in surviving patients, however, was significantly higher in patients with severe acquired ADAMTS-13 deficiency than in those without (6/14 vs. 2/25) [30]. Raife et al. [116] reported higher median creatinine levels, less severe thrombocytopenia, and lower relapse rate in non-severely ADAMTS-13 deficient when compared with severely deficient patients with acute TMA.

The relapse rate in survivors of TTP is high (up to 36%), recurrences may occur many years after a first attack [29], but are most frequent during the first year after disease onset [31]. Patients with severe acquired ADAMTS-13 deficiency usually lose their circulating inhibitors and normalize their ADAMTS-13 activity after obtaining a clinical remission [24,26], but some patients achieve remission despite remaining severely deficient [25,114,117,118]. Zheng et al. [114] found that patients with high titer inhibitors at presentation usually remained severely deficient in ADAMTS-13 activity in early remission and had a high relapse risk. On the contrary, we followed up a patient who was splenectomized because of plasma-refractory TTP due to autoantibody-mediated severe ADAMTS-13 deficiency [119]. Three years after splenectomy, a high titer autoantibody leading to complete disappearance of protease activity reappeared, the patient nevertheless remaining asymptomatic for more than 32 months.

Patients with TMA after hematopoietic stem cell transplantation consistently had measurable ADAMTS-13 activity [30,112,120–122] as did most patients with neoplasia- or anticancer treatment-associated TMA [112,123]. TMA induced by ticlopidine [124] and possibly by clopidogrel [125], on the contrary, was reported to be associated with autoantibody-mediated severe ADAMTS-13 deficiency, as were several – though not all – cases of postpartum- or pregnancy-associated TMA [11,30,114]. D+ HUS was generally not associated with severe ADAMTS-13 deficiency [126,127] whereby one of 29 children in the latter study had a transiently lacking protease activity caused by an autoantibody [127]. None of 120 plasma samples from patients having been diagnosed with HUS, referred to our laboratory between January 2001 and July 2003, had a severe ADAMTS-13 deficiency [112].

The annual incidence of TTP has been estimated to be 3.7 per million population [128]. The Oklahoma TTP-HUS registry has recently calculated age-, sex-, and race-standardized incidence rates for all patients with a TTP-HUS syndrome referred for plasma exchange therapy (thus excluding childhood D+ HUS), for idiopathic TTP, and for those with severe ADAMTS-13 deficiency, the figures being 11.3, 4.5 and 1.7/106 per annum, respectively [129].

Treatment of TTP

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

Treatment of TTP has been reviewed by several authors [9,12,33,130] and guidelines have been proposed by the British Committee for the Standardization in Haematology [131] even though levels of evidence on which recommendations are based are mostly weak, i.e. level IV. Still, the dramatic improvement of survival from approximately 10% to 80% by the empirical introduction of plasma exchange and FFP replacement in the 1970s [27] certainly forbids to undertake a randomized study with a control group not receiving plasma therapy. Moreover, the Canadian Apheresis Study Group [28], in a prospective controlled trial on 102 patients demonstrated that plasma exchange of 1.5 plasma volumes daily for 3 days, followed by exchanges of 1 volume daily, and FFP replacement was superior to simple FFP infusion, response rates after the first treatment cycle and at 6 months being 47% and 78% vs. 25% and 49%, respectively, and mortality being 22% vs. 37%. Corticosteroids have been frequently used in addition, and sometimes alone in milder cases [32] and were often found to be useful. In light of the recent findings that many patients with acute TTP have severe autoantibody-induced ADAMTS-13 deficiency, a pathophysiological basis for these approaches seems to be at hand: plasma exchange may remove autoantibodies, FFP replaces the lacking protease and corticosteroids may suppress autoantibody formation. Cryosupernatant, lacking the larger plasma VWF multimers, has been used as replacement fluid instead of plasma and seemed to be more efficacious if compared with a historical control group in which FFP was used [132]. However, this has not been substantiated in subsequent randomized studies [133,134].

Plasma-refractory TTP patients or relapsing patients are often treated with more intensive plasma exchange regimens, e.g. twice daily. Splenectomy, best performed in remission after relapse, seemed to be often effective [135–137], its beneficial effect may mainly relate to elimination of autoantibody-producing B cells [24,119], even though other mechanisms may underlie its beneficial effects [117]. Recently, several patients with relapsing TTP caused by autoimmune-mediated ADAMTS-13 deficiency have been treated with rituximab, a monoclonal anti-CD20 antibody, and successful short-term outcomes have been reported [138–143]. Whether there is any long-term advantage over corticosteroids, other immunosuppressive treatment or splenectomy, needs to be tested in prospective trials.

There has been controversy as to whether plasma exchange therapy would be indicated for those patients with clinically diagnosed TTP not having autoantibody-mediated severe ADAMTS-13 deficiency. A small retrospective study from Japan [111] showed that 10 of 12 TTP patients with severe acquired ADAMTS-13 deficiency survived, whereas four of six without severe deficiency died despite plasma exchange treatment. In contrast, among the 48 patients with idiopathic TTP reported by Vesely et al. [30], three of 16 patients with and seven of 32 without severe acquired ADAMTS-13 deficiency died of their disease, thus plasma exchange seemed to be effective also in the latter patients. Zheng et al. [114], based on their experience with 37 patients, also questioned the indication for plasma exchange in patients without severe ADAMTS-13 deficiency. However, our interpretation of their data is that outcome was rather related to the clinical diagnosis than to ADAMTS-13 levels: 10 of 17 patients with secondary TMA (many associated with hematopoietic stem cell transplantation, neoplasia or anticancer agents), all having normal or mildly reduced ADAMTS-13 activity, died whereas only three of 20 patients with idiopathic TTP succumbed, notably three of 16 with severe ADAMTS-13 deficiency but none of four without.

Thus, based on present knowledge, plasma exchange therapy with FFP replacement clearly remains mandatory, at least for all patients with idiopathic TTP, also in the absence of severe acquired ADAMTS-13 deficiency.

Constitutional TTP caused by homozygous or double heterozygous ADAMTS-13 gene defects may be treated by simple FFP infusion [11,34] and relapses may be prevented by regular FFP infusion every 2–3 weeks, in some patients with frequent recurrences over many years [78]. The ADAMTS-13 has an in vivo half-life in plasma of about 2–4 days [144] and ADAMTS-13 activity after infusion of 1–2 U of FFP may rise to only about 10–20% of normal. It is not quite clear why the effect on platelet count will last for up to 3 weeks, because the plasma level will fall below 5% within some 3–8 days. One may speculate that ADAMTS-13 remains available, e.g. on the microvascular endothelial surface, for longer than anticipated from its plasma levels.

Diarrhea-positive HUS in children is generally treated by supportive therapy using renal dialysis as required, and plasma infusion or exchange has not been found to improve outcome [131]. In a cohort of elderly nursing home residents with D+ HUS, plasma exchange with FFP replacement was performed in 16 of 22 patients without evidence of clear benefit [145]. Activation of coagulation with high prothrombin fragment F1 + 2 concentrations has been reported in children with D+ HUS [146] and in an animal model, lepirudin prevented death from HUS in two of three dogs challenged with shiga-like toxin [147]. Thus, thrombin inhibition may be a therapeutic strategy to be further explored in D+ HUS.

Effective treatment for hematopoietic stem cell transplantation- or neoplasia-associated TMA is unknown, plasma exchange is often used but in severe cases the mortality rate is very high with death occurring either from the underlying neoplasia or the TMA itself.

Conclusion and research agenda

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

Despite exciting pathophysiologic advances achieved in recent years, many questions concerning diagnosis, pathogenesis and treatment of the thrombotic microangiopathies remain to be answered.

  • 1
    An important point is clarification of terminology. TTP, HUS, TTP-HUS, idiopathic TTP, secondary TTP, TTP-like disease, typical HUS (D+ HUS) and atypical HUS (D− HUS) are too many terms for partly overlapping, partly distinct, and pathophysiologically only partially clarified disease states. We propose to use the comprehensive term TMA for all these disease states with schistocytic hemolysis and consumptive thrombocytopenia and to list: (i) idiopathic TTP with hereditary severe ADAMTS-13 deficiency, (ii) idiopathic TTP with and (iii) without severe acquired ADAMTS-13 deficiency as distinct entities (the latter as provisional category, until its pathophysiology is better characterized). D+ HUS caused by enterohemorrhagic E. coli infection should be considered a separate entity as well, and the role of factor H deficiency or mutations [148–152] as causal for atypical HUS should be further investigated. It is probably justified to provisionally list other disease states as TMA associated with the underlying condition, such as neoplasia, anticancer agents, hematopoietic stem cell transplantation, until their pathogenesis will be unravelled.
  • 2
    Quantitation of red cell fragmentation [153] should be more widely introduced in the clinical laboratory. Some schistocytes are seen in many conditions such as DIC, sepsis and others, usually in much lower numbers than in clear-cut TTP or HUS.
  • 3
    It would be extremely useful to reinvestigate the histological patterns of microvascular thrombi in several forms of TMA. These microthrombi are said to consist mainly of platelets and VWF in TTP [2,3], but rather of fibrin in D+ HUS [3,126]. If confirmed, the presumed difference in pathogenesis will be further substantiated, and additional histopathologic studies may further our insight into the pathophysiology of other TMA, e.g. idiopathic TTP without severe ADAMTS-13 deficiency.
  • 4
    Similarly, it will be interesting to evaluate whether exaggerated thrombin generation is specific for D+ HUS [146] and whether activation markers of plasmatic coagulation and fibrinolysis can help to distinguish other forms of TMA. It should be recalled, that elevated coagulation activation markers have also been reported in TTP [154].
  • 5
    An important topic will be to find out whether idiopathic TTP without severe ADAMTS-13 deficiency as measured by static assays is still related to an altered ADAMTS-13-VWF interaction in vivo. Further structure-function studies of ADAMTS-13 and search for possible autoantibodies not inhibiting ADAMTS-13 protease activity in traditional assays but precluding its binding to endothelium-anchored ULVWF are needed.
  • 6
    Cofactors for triggering disease onset in severe hereditary or acquired ADAMTS-13 deficiency should be investigated to clarify why some patients with severely deficient protease activity consistently relapse every few weeks [11], whereas others remain asymptomatic into their forties.
  • 7
    The true frequency of hereditary TTP needs to be re-evaluated, this condition having been largely ignored or misdiagnosed. A registry of such patients will certainly be helpful to sensitize physicians and improve the health of affected patients.
  • 8
    Having identified twin sisters who developed autoantibody-mediated ADAMTS-13 deficiency and TTP 1 year apart [118] the question arises as to whether a genetic predisposition to ADAMTS-13 autoimmunity can be identified.
  • 9
    The role of persisting or recurring acquired ADAMTS-13 deficiency in survivors of acute TTP as a prognostic marker needs to be addressed, because it may allow to prevent relapses at an asymptomatic state using immunosuppressive treatment.
  • 10
    Finally, the role of ADAMTS-13 in platelets [47] has to be investigated, both in terms of its physiological role and with respect as to whether a platelet reservoir of ADAMTS-13 may be protective even in the absence of any plasma ADAMTS-13 activity.
  • 11
    TTP and the other TMA have attracted and continue to attract many researchers. Many controversies have been raised and debates are likely to go on. It is hoped that continuing research into the pathophysiology and treatment of the TMA will further benefit affected patients who are still at high risk of premature and often preventable death.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References

We dedicate this paper to our friend, Professor Miha Furlan, who until his retirement in 2000 guided the research project on von Willebrand factor-cleaving protease at our institute, made most important contributions to the field, and still follows with great interest and helpful advice our continuing research. Irmela Sulzer is acknowledged for technical assistance.

Studies from our laboratory are supported by the Swiss National Science Foundation (grant no. 32-66756.01 and 32-65337.01), the Fondation pour la Recherche sur l’ Arteriosclérose et la Thrombose, and by the Mach-Gaensslen Foundation Switzerland.

References

  1. Top of page
  2. Abstract
  3. Historical aspects of thrombotic thrombocytopenic purpura (1924–1998)
  4. Cloning, structure and function of the von Willebrand factor-cleaving protease (ADAMTS-13)
  5. ADAMTS-13 assays
  6. Hereditary TTP
  7. Acquired TTP
  8. Treatment of TTP
  9. Conclusion and research agenda
  10. Acknowledgements
  11. References
  • 1
    Moschcowitz E. Hyaline thrombosis of the terminal arterioles and capillaries: a hitherto undescribed disease. Proc N Y Pathol Soc 1924; 24: 214.
  • 2
    Asada Y, Sumiyoshi A, Hayashi T, Suzumiya J, Kaketani K. Immunohistochemistry of vascular lesion in thrombotic thrombocytopenic purpura, with special reference to factor VIII related antigen. Thromb Res 1985; 38: 46979.
  • 3
    Hosler GA, Cusumano AM, Hutchins GM. Thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are distinct pathologic entities. A review of 56 autopsy cases. Arch Pathol Lab Med 2003; 127: 8349.
  • 4
    Moschcowitz E. An acute febrile pleiochromic anemia with hyaline thrombosis of the terminal arterioles and capillaries. Arch Intern Med 1925; 36: 8993.
  • 5
    Amorosi EL, Ultmann JE. Thrombotic thrombocytopenic purpura: report of 16 cases and review of the literature. Medicine (Baltimore) 1966; 45: 13959.
  • 6
    Gasser C, Gautier E, Steck A, Siebenmann RE, Oechslin R. Hämolytisch-urämische Syndrome: bilaterale Nierenrindennekrosen bei akuten erworbenen hämolytischen Anämien. Schweiz Med Wochenschr 1955; 85: 9059.
  • 7
    Griffin PM, Tauxe RV. The epidemiology of infections caused by Escherichia coli O157:H7, other enterohemorrhagic E. coli, and the associated hemolytic uremic syndrome. Epidemiol Rev 1991; 13: 6098.
  • 8
    Ruggenenti P, Remuzzi G. The pathophysiology and management of thrombotic thrombocytopenic purpura. Eur J Haematol 1996; 56: 191207.
  • 9
    George JN. How I treat patients with thrombotic thrombocytopenic purpura-hemolytic uremic syndrome. Blood 2000; 96: 12239.
  • 10
    Moake JL, Chow TW. Thrombotic thrombocytopenic purpura: understanding a disease no longer rare. Am J Med Sci 1998; 316: 105119.
  • 11
    Furlan M, Lämmle B. Aetiology and pathogenesis of thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome: the role of von Willebrand factor-cleaving protease. Best Pract Res Clin Haematol 2001; 14: 43754.
  • 12
    Moake JL. Thrombotic microangiopathies. N Engl J Med 2002; 347: 589600.
  • 13
    Tandon NN, Rock G, Jamieson GA. Anti-CD36 antibodies in thrombotic thrombocytopenic purpura. Br J Haematol 1994; 88: 81625.
  • 14
    Schultz DR, Arnold PI, Jy W, Valant PA, Gruber J, Ahn YS, Mao FW, Mao WW, Horstman LL. Anti-CD36 autoantibodies in thrombotic thrombocytopenic purpura and other thrombotic disorders: identification of an 85 kD form of CD36 as a target antigen. Br J Haematol 1998; 103: 84957.
  • 15
    Laurence J, Mitra D, Steiner M, Staiano-Coico L, Jaffe E. Plasma from patients with idiopathic and human immunodeficiency virus-associated thrombotic thrombocytopenic purpura induces apoptosis in microvascular endothelial cells. Blood 1996; 87: 324554.
  • 16
    Siddiqui FA, Lian EC. Novel platelet-agglutinating protein from a thrombotic thrombocytopenic purpura plasma. J Clin Invest 1985; 76: 13307.
  • 17
    Murphy WG, Moore JC, Kelton JG. Calcium-dependent cysteine protease activity in the sera of patients with thrombotic thrombocytopenic purpura. Blood 1987; 70: 16837.
  • 18
    Kelton JG, Moore JC, Warkentin TE, Hayward CP. Isolation and characterization of cysteine proteinase in thrombotic thrombocytopenic purpura. Br J Haematol 1996; 93: 4216.
  • 19
    Moake JL, Rudy CK, Troll JH, Weinstein MJ, Colannino NM, Azocar J, Seder RH, Hong SL, Deykin D. Unusually large plasma factor VIII:von Willebrand factor multimers in chronic relapsing thrombotic thrombocytopenic purpura. N Engl J Med 1982; 307: 14325.
  • 20
    Furlan M, Robles R, Lämmle B. Partial purification and characterization of a protease from human plasma cleaving von Willebrand factor to fragments produced by in vivo proteolysis. Blood 1996; 87: 422334.
  • 21
    Tsai HM. Physiologic cleavage of von Willebrand factor by a plasma protease is dependent on its conformation and requires calcium ion. Blood 1996; 87: 423544.
  • 22
    Dent JA, Berkowitz SD, Ware J, Kasper CK, Ruggeri ZM. Identification of a cleavage site directing the immunochemical detection of molecular abnormalities in type IIA von Willebrand factor. Proc Natl Acad Sci USA 1990; 87: 630610.
  • 23
    Furlan M, Robles R, Solenthaler M, Wassmer M, Sandoz P, Lämmle B. Deficient activity of von Willebrand factor-cleaving protease in chronic relapsing thrombotic thrombocytopenic purpura. Blood 1997; 89: 3097103.
  • 24
    Furlan M, Robles R, Solenthaler M, Lämmle B. Acquired deficiency of von Willebrand factor-cleaving protease in a patient with thrombotic thrombocytopenic purpura. Blood 1998; 91: 283946.
  • 25
    Furlan M, Robles R, Galbusera M, Remuzzi G, Kyrle PA, Brenner B, Krause M, Scharrer I, Aumann V, Mittler U, Solenthaler M, Lämmle B. Von Willebrand factor-cleaving protease in thrombotic thrombocytopenic purpura and the hemolytic-uremic syndrome. N Engl J Med 1998; 339: 157884.
  • 26
    Tsai HM, Lian EC. Antibodies to von Willebrand factor-cleaving protease in acute thrombotic thrombocytopenic purpura. N Engl J Med 1998; 339: 158594.
  • 27
    Byrnes JJ, Khurana M. Treatment of thrombotic thrombocytopenic purpura with plasma. N Engl J Med 1977; 297: 13869.
  • 28
    Rock GA, Shumak KH, Buskard NA, Blanchette VS, Kelton JG, Nair RC, Spasoff RA. Comparison of plasma exchange with plasma infusion in the treatment of thrombotic thrombocytopenic purpura. Canadian Apheresis Study Group. N Engl J Med 1991; 325: 3937.
  • 29
    Shumak KH, Rock GA, Nair RC. Late relapses in patients successfully treated for thrombotic thrombocytopenic purpura. Canadian Apheresis Group. Ann Intern Med 1995; 122: 56972.
  • 30
    Vesely SK, George JN, Lämmle B, Studt JD, Alberio L, El-Harake MA, Raskob GE. ADAMTS-13 activity in thrombotic thrombocytopenic purpura-hemolytic uremic syndrome: relation to presenting features and clinical outcomes in a prospective cohort of 142 patients. Blood 2003; 102: 608.
  • 31
    Sadler JE, Moake JL, Miyata T, George JN. Recent advances in thrombotic thrombocytopenic purpura. Hematology (Am Soc Hematol Educ Program) 2004; 40723.
  • 32
    Bell WR, Braine HG, Ness PM, Kickler TS. Improved survival in thrombotic thrombocytopenic purpura-hemolytic uremic syndrome. Clinical experience in 108 patients. N Engl J Med 1991; 325: 398403.
  • 33
    Rock GA. Management of thrombotic thrombocytopenic purpura. Br J Haematol 2000; 109: 496507.
  • 34
    Upshaw JD. Congenital deficiency of a factor in normal plasma that reverses microangiopathic hemolysis and thrombocytopenia. N Engl J Med 1978; 298: 13502.
  • 35
    Schulman I, Pierce M, Lukens A, Currimbhoy Z. Studies on thrombopoiesis. I: a factor in normal human plasma required for platelet production; chronic thrombocytopenia due to its deficiency. Blood 1960; 16: 94357.
  • 36
    Furlan M. Proteolytic cleavage of von Willebrand factor by ADAMTS-13 prevents uninvited clumping of blood platelets. J Thromb Haemost 2004; 2: 15059.
  • 37
    Tsai HM. A journey from sickle cell anemia to ADAMTS-13. J Thromb Haemost 2004; 2: 15104.
  • 38
    Moake JL. Defective processing of unusually large von Willebrand factor multimers and thrombotic thrombocytopenic purpura. J Thromb Haemost 2004; 2: 151521.
  • 39
    Gerritsen HE, Robles R, Lämmle B, Furlan M. Partial amino acid sequence of purified von Willebrand factor-cleaving protease. Blood 2001; 98: 165461.
  • 40
    Fujikawa K, Suzuki H, McMullen B, Chung D. Purification of human von Willebrand factor-cleaving protease and its identification as a new member of the metalloproteinase family. Blood 2001; 98: 16626.
  • 41
    Soejima K, Mimura N, Hirashima M, Maeda H, Hamamoto T, Nakagaki T, Nozaki C. A novel human metalloprotease synthesized in the liver and secreted into the blood: possibly, the von Willebrand factor-cleaving protease? J Biochem (Tokyo) 2001; 130: 47580.
  • 42
    Zheng X, Chung D, Takayama TK, Majerus EM, Sadler JE, Fujikawa K. Structure of von Willebrand factor-cleaving protease (ADAMTS-13), a metalloprotease involved in thrombotic thrombocytopenic purpura. J Biol Chem 2001; 276: 4105963.
  • 43
    Levy GG, Nichols WC, Lian EC, Foroud T, McClintick JN, McGee BM, Yang AY, Siemieniak DR, Stark KR, Gruppo R, Sarode R, Shurin SB, Chandrasekaran V, Stabler SP, Sabio H, Bouhassira EE, Upshaw JD Jr, Ginsburg D, Tsai HM. Mutations in a member of the ADAMTS gene family cause thrombotic thrombocytopenic purpura. Nature 2001; 413: 48894.
  • 44
    Plaimauer B, Scheiflinger F. Expression and characterization of recombinant human ADAMTS-13. Semin Hematol 2004; 41: 2433.
  • 45
    Lee TP, Bouhassira EE, Lyubsky S, Tsai HM. ADAMTS-13, the von Willebrand factor cleaving metalloprotease, is expressed in the perisinusoidal cells of the liver. Blood 2002; 100: Abstract no. 1938.
  • 46
    Plaimauer B, Zimmermann K, Volkel D, Antoine G, Kerschbaumer R, Jenab P, Furlan M, Gerritsen H, Lämmle B, Schwarz HP, Scheiflinger F. Cloning, expression, and functional characterization of the von Willebrand factor-cleaving protease (ADAMTS-13). Blood 2002; 100: 362632.
  • 47
    Suzuki M, Murata M, Matsubara Y, Uchida T, Ishihara H, Shibano T, Ashida S, Soejima K, Okada Y, Ikeda Y. Detection of von Willebrand factor-cleaving protease (ADAMTS-13) in human platelets. Biochem Biophys Res Commun 2004; 313: 2126.
  • 48
    Kokame K, Matsumoto M, Soejima K, Yagi H, Ishizashi H, Funato M, Tamai H, Konno M, Kamide K, Kawano Y, Miyata T, Fujimura Y. Mutations and common polymorphisms in ADAMTS-13 gene responsible for von Willebrand factor-cleaving protease activity. Proc Natl Acad Sci USA 2002; 99: 119027.
  • 49
    Soejima K, Matsumoto M, Kokame K, Yagi H, Ishizashi H, Maeda H, Nozaki C, Miyata T, Fujimura Y, Nakagaki T. ADAMTS-13 cysteine-rich/spacer domains are functionally essential for von Willebrand factor cleavage. Blood 2003; 102: 32327.
  • 50
    Zheng X, Nishio K, Majerus EM, Sadler JE. Cleavage of von Willebrand factor requires the spacer domain of the metalloprotease ADAMTS-13. J Biol Chem 2003; 278: 3013641.
  • 51
    Antoine G, Zimmermann K, Plaimauer B, Grillowitzer M, Studt JD, Lämmle B, Scheiflinger F. ADAMTS-13 gene defects in two brothers with constitutional thrombotic thrombocytopenic purpura and normalization of von Willebrand factor-cleaving protease activity by recombinant human ADAMTS-13. Br J Haematol 2003; 120: 8214.
  • 52
    Tsai HM, Sussman II, Nagel RL. Shear stress enhances the proteolysis of von Willebrand factor in normal plasma. Blood 1994; 83: 21719.
  • 53
    Schneppenheim R, Budde U, Oyen F, Angerhaus D, Aumann V, Drewke E, Hassenpflug W, Häberle J, Kentouche K, Kohne E, Kurnik K, Mueller-Wiefel D, Obser T, Santer R, Sykora KW. Von Willebrand factor cleaving protease and ADAMTS-13 mutations in childhood TTP. Blood 2003; 101: 184550.
  • 54
    Studt JD, Kremer Hovinga JA, Antoine G, Hermann M, Rieger M, Scheiflinger F, Lämmle B. Fatal congenital thrombotic thrombocytopenic purpura with apparent ADAMTS-13 inhibitor: in vitro inhibition of ADAMTS-13 activity by hemoglobin. Blood 2005; 105: 5424.
  • 55
    Majerus EM, Zheng X, Tuley EA, Sadler JE. Cleavage of the ADAMTS-13 propeptide is not required for protease activity. J Biol Chem 2003; 278: 466438.
  • 56
    Dong JF, Moake JL, Bernardo A, Fujikawa K, Ball C, Nolasco L, Lopez JA, Cruz MA. ADAMTS-13 metalloprotease interacts with the endothelial cell-derived ultra-large von Willebrand factor. J Biol Chem 2003; 278: 296339.
  • 57
    Dong JF, Moake JL, Nolasco L, Bernardo A, Arceneaux W, Shrimpton CN, Schade AJ, McIntire LV, Fujikawa K, Lopez JA. ADAMTS-13 rapidly cleaves newly secreted ultralarge von Willebrand factor multimers on the endothelial surface under flowing conditions. Blood 2002; 100: 40339.
  • 58
    Padilla A, Moake JL, Bernardo A, Ball C, Wang Y, Arya M, Nolasco L, Turner N, Berndt MC, Anvari B, Lopez JA, Dong JF. P-selectin anchors newly released ultralarge von Willebrand factor multimers to the endothelial cell surface. Blood 2004; 103: 21506.
  • 59
    Lopez JA, Dong JF. Cleavage of von Willebrand factor by ADAMTS-13 on endothelial cells. Semin Hematol 2004; 41: 1523.
  • 60
    Furlan M, Lämmle B. Assays of von Willebrand factor-cleaving protease: a test for diagnosis of familial and acquired thrombotic thrombocytopenic purpura. Semin Thromb Hemost 2002; 28: 16772.
  • 61
    Veyradier A, Girma JP. Assays of ADAMTS-13 activity. Semin Hematol 2004; 41: 417.
  • 62
    Gerritsen HE, Turecek PL, Schwarz HP, Lämmle B, Furlan M. Assay of von Willebrand factor (vWF)-cleaving protease based on decreased collagen binding affinity of degraded vWF: a tool for the diagnosis of thrombotic thrombocytopenic purpura (TTP). Thromb Haemost 1999; 82: 13869.
  • 63
    Böhm M, Vigh T, Scharrer I. Evaluation and clinical application of a new method for measuring activity of von Willebrand factor-cleaving metalloprotease (ADAMTS-13). Ann Hematol 2002; 81: 4305.
  • 64
    Obert B, Tout H, Veyradier A, Fressinaud E, Meyer D, Girma JP. Estimation of the von Willebrand factor-cleaving protease in plasma using monoclonal antibodies to vWF. Thromb Haemost 1999; 82: 13825.
  • 65
    Studt JD, Böhm M, Budde U, Girma JP, Varadi K, Lämmle B. Measurement of von Willebrand factor-cleaving protease (ADAMTS-13) activity in plasma: a multicenter comparison of different assay methods. J Thromb Haemost 2003; 1: 18827.
  • 66
    Tripodi A, Chantarangkul V, Bohm M, Budde U, Dong JF, Friedman KD, Galbusera M, Girma JP, Moake J, Rick ME, Studt JD, Turecek PL, Mannucci PM. Measurement of von Willebrand factor cleaving protease (ADAMTS-13): results of an international collaborative study involving 11 methods testing the same set of coded plasmas. J Thromb Haemost 2004; 2: 16019.
  • 67
    Kinoshita S, Yoshioka A, Park YD, Ishizashi H, Konno M, Funato M, Matsui T, Titani K, Yagi H, Matsumoto M, Fujimura Y. Upshaw-Schulman syndrome revisited: a concept of congenital thrombotic thrombocytopenic purpura. Int J Hematol 2001; 74: 1018.
  • 68
    Dong JF, Whitelock J, Bernardo A, Ball C, Cruz MA. Variations among normal individuals in the cleavage of endothelial-derived ultra-large von Willebrand factor under flow. J Thromb Haemost 2004; 2: 14606.
  • 69
    Remuzzi G, Galbusera M, Noris M, Canciani MT, Daina E, Bresin E, Contaretti S, Caprioli J, Gamba S, Ruggenenti P, Perico N, Mannucci PM. von Willebrand factor cleaving protease (ADAMTS-13) is deficient in recurrent and familial thrombotic thrombocytopenic purpura and hemolytic uremic syndrome. Blood 2002; 100: 77885.
  • 70
    Whitelock JL, Nolasco L, Bernardo A, Moake J, Dong JF, Cruz MA. ADAMTS-13 activity in plasma is rapidly measured by a new ELISA method that uses recombinant VWF-A2 domain as substrate. J Thromb Haemost 2004; 2: 48591.
  • 71
    Kokame K, Matsumoto M, Fujimura Y, Miyata T. VWF73, a region from D1596 to R1668 of von Willebrand factor, provides a minimal substrate for ADAMTS-13. Blood 2004; 103: 60712.
  • 72
    Kokame K, Nobe Y, Kokubo Y, Okayama A, Miyata T. FRETS-VWF73, a first fluorogenic substrate for ADAMTS-13 assay. Br J Haematol 2005; 129: 93100.
  • 73
    Scheiflinger F, Knöbl P, Trattner B, Plaimauer B, Mohr G, Dockal M, Dorner F, Rieger M. Non-neutralizing IgM and IgG antibodies to von Willebrand factor-cleaving protease (ADAMTS-13) in a patient with thrombotic thrombocytopenic purpura. Blood 2003; 102: 32413.
  • 74
    Häberle J, Kehrel B, Ritter J, Jürgens H, Lämmle B, Furlan M. New strategies in diagnosis and treatment of thrombotic thrombocytopenic purpura: case report and review. Eur J Pediatr 1999; 158: 8837.
  • 75
    Allford SL, Harrison P, Lawrie AS, Liesner R, MacKie IJ, Machin SJ. Von Willebrand factor-cleaving protease activity in congenital thrombotic thrombocytopenic purpura. Br J Haematol 2000; 111: 121522.
  • 76
    te Loo DM, Levtchenko E, Furlan M, Roosendaal GP, van den Heuvel LP. Autosomal recessive inheritance of von Willebrand factor-cleaving protease deficiency. Pediatr Nephrol 2000; 14: 7625.
  • 77
    Sasahara Y, Kumaki S, Ohashi Y, Minegishi M, Kano H, Bessho F, Tsuchiya S. Deficient activity of von Willebrand factor-cleaving protease in patients with Upshaw-Schulman syndrome. Int J Hematol 2001; 74: 10914.
  • 78
    Barbot J, Costa E, Guerra M, Barreirinho MS, Isvarlal P, Robles R, Gerritsen HE, Lämmle B, Furlan M. Ten years of prophylactic treatment with fresh-frozen plasma in a child with chronic relapsing thrombotic thrombocytopenic purpura as a result of a congenital deficiency of von Willebrand factor-cleaving protease. Br J Haematol 2001; 113: 64951.
  • 79
    Stark GL, Wallis JP, Allford SL, Hanley J. Chronic relapsing thrombotic thrombocytopenic purpura due to a deficiency of von Willebrand factor-cleaving protease activity. Br J Haematol 2002; 117: 2512.
  • 80
    Lester WA, Williams MD, Allford SL, Enayat MS, Machin SJ. Successful treatment of congenital thrombotic thrombocytopenic purpura using the intermediate purity factor VIII concentrate BPL 8Y. Br J Haematol 2002; 119: 1769.
  • 81
    Kentouche K, Budde U, Furlan M, Scharfe V, Schneppenheim R, Zintl F. Remission of thrombotic thrombocytopenic purpura in a patient with compound heterozygous deficiency of von Willebrand factor-cleaving protease by infusion of solvent/detergent plasma. Acta Paediatr 2002; 91: 10569.
  • 82
    Studt JD, Kremer Hovinga JA, Alberio L, Bianchi V, Lämmle B. Von Willebrand factor-cleaving protease (ADAMTS-13) activity in thrombotic microangiopathies: diagnostic experience 2001/2002 of a single research laboratory. Swiss Med Wkly 2003; 133: 32532.
  • 83
    Schiff DE, Roberts WD, Willert J, Tsai HM. Thrombocytopenia and severe hyperbilirubinemia in the neonatal period secondary to congenital thrombotic thrombocytopenic purpura and ADAMTS-13 deficiency. J Pediatr Hematol Oncol 2004; 26: 5358.
  • 84
    Veyradier A, Obert B, Haddad E, Cloarec S, Nivet H, Foulard M, Lesure F, Delattre P, Lakhdari M, Meyer D, Girma JP, Loirat C. Severe deficiency of the specific von Willebrand factor-cleaving protease (ADAMTS 13) activity in a subgroup of children with atypical hemolytic uremic syndrome. J Pediatr 2003; 142: 3107.
  • 85
    Hellman RM, Jackson DV, Buss DH. Thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome in HLA-identical siblings. Ann Intern Med 1980; 93: 2834.
  • 86
    Elias M, Horowitz J, Tal I, Kohn D, Flatau E. Thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome in three siblings. Arch Dis Child 1988; 63: 6446.
  • 87
    Motto D, Levy G, McGee B, Tsai HM, Ginsburg D. ADAMTS-13 mutations identified in familial TTP patients result in loss of VWF-cleaving protease activity. Blood 2002; 100: Abstract no. 44.
  • 88
    Assink K, Schiphorst R, Allford S, Karpman D, Etzioni A, Brichard B, van de Kar N, Monnens L, van den Heuvel L. Mutation analysis and clinical implications of von Willebrand factor-cleaving protease deficiency. Kidney Int 2003; 63: 19959.
  • 89
    Savasan S, Lee SK, Ginsburg D, Tsai HM. ADAMTS-13 gene mutation in congenital thrombotic thrombocytopenic purpura with previously reported normal VWF cleaving protease activity. Blood 2003; 101: 444951.
  • 90
    Bestetti G, Stellari A, Lattuada A, Corbellino M, Parravicini C, Calzarossa C, Cenzuales S, Moroni M, Galli M, Rossi E. ADAMTS 13 genotype and vWF protease activity in an Italian family with TTP. Thromb Haemost 2003; 90: 9556.
  • 91
    Veyradier A, Lavergne JM, Ribba AS, Obert B, Loirat C, Meyer D, Girma JP. Ten candidate ADAMTS-13 mutations in six French families with congenital thrombotic thrombocytopenic purpura (Upshaw-Schulman syndrome). J Thromb Haemost 2004; 2: 4249.
  • 92
    Uchida T, Wada H, Mizutani M, Iwashita M, Ishihara H, Shibano T, Suzuki M, Matsubara Y, Soejima K, Matsumoto M, Fujimura Y, Ikeda Y, Murata M. Identification of novel mutations in ADAMTS-13 in an adult patient with congenital thrombotic thrombocytopenic purpura. Blood 2004; 104: 20813.
  • 93
    Matsumoto M, Kokame K, Soejima K, Miura M, Hayashi S, Fujii Y, Iwai A, Ito E, Tsuji Y, Takeda-Shitaka M, Iwadate M, Umeyama H, Yagi H, Ishizashi H, Banno F, Nakagaki T, Miyata T, Fujimura Y. Molecular characterization of ADAMTS-13 gene mutations in Japanese patients with Upshaw-Schulman syndrome. Blood 2004; 103: 130510.
  • 94
    Pimanda JE, Maekawa A, Wind T, Paxton J, Chesterman CN, Hogg PJ. Congenital thrombotic thrombocytopenic purpura in association with a mutation in the second CUB domain of ADAMTS-13. Blood 2004; 103: 6279.
  • 95
    Kremer Hovinga JA, Siebke E, Mäder G, Studt JD, Oppliger Leibundgut E, Wermuth B, Lämmle B. Hereditary thrombotic thrombocytopenic purpura caused by a new ADAMTS-13 mutation, Cysteine 804 to Arginine. Hämostaseologie 2004; 24: Abstract no. V44.
  • 96
    Peyvandi F, Ferrari S, Lavoretano S, Canciani MT, Mannucci PM. Willebrand factor cleaving protease (ADAMTS-13) and ADAMTS-13 neutralizing autoantibodies in 100 patients with thrombotic thrombocytopenic purpura. Br J Haematol 2004; 127: 4339.
  • 97
    Licht C, Stapenhorst L, Simon T, Budde U, Schneppenheim R, Hoppe B. Two novel ADAMTS-13 gene mutations in thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome (TTP/HUS). Kidney Int 2004; 66: 9558.
  • 98
    Snider CE, Moore JC, Warkentin TE, Finch CN, Hayward CP, Kelton JG. Dissociation between the level of von Willebrand factor-cleaving protease activity and disease in a patient with congenital thrombotic thrombocytopenic purpura. Am J Hematol 2004; 77: 38790.
  • 99
    Donadelli R, Banterla F, Capoferri C, Galbusera M, Ruggeri ZM, Bucchioni S, Noris M, Remuzzi G. Diverse functional implications of ADAMTS-13 gene mutations in patients with TTP and congenital deficiency. Blood 2004; 104: Abstract no. 513.
  • 100
    Peyvandi F, Lavoretano S, De Cristofaro R, Valsecchi C, Merati G, Lattuada A, Mannucci PM. In vitro expression studies of two mutations on the metalloprotease and first CUB domains of the ADAMTS-13 gene leading to severe ADAMTS-13 deficiency and chronic recurrent TTP. Blood 2004; 104: Abstract no. 514.
  • 101
    Tao Z, Nolasco L, Aubrey B, Rice L, Moake JF, Dong JF. An in-frame deletion of six amino acids and a point mutation in the disintegrin domain of ADAMTS-13 associates with a case of congenital thrombotic thrombocytopenic purpura. Blood 2004; 104: Abstract no. 854.
  • 102
    Schneppenheim R, Budde U, Hassenpflug W, Obser T. Severe ADAMTS-13 deficiency in childhood. Semin Hematol 2004; 41: ?hangover 0>839.
  • 103
    Fuchs WE, George JN, Dotin LN, Sears DA. Thrombotic thrombocytopenic purpura. Occurrence two years apart during late pregnancy in two sisters. Jama 1976; 235: 21267.
  • 104
    George JN. The association of pregnancy with thrombotic thrombocytopenic purpura-hemolytic uremic syndrome. Curr Opin Hematol 2003; 10: 33944.
  • 105
    Schneppenheim R, Kremer Hovinga JA, Budde U, Karpman D, Brockhaus W, Korczowski B, Milosevic D, Oyen F, von Rosen J, Tjønnfjord GE, Pimanda JE, Lämmle B. A Baltic origin of the common ADAMTS-13 mutation 4143insA. Hämostaseologie 2005; 25: Abstract No. V125.
  • 106
    Loof AH, van Vliet HH, Kappers-Klunne MC. Low activity of von Willebrand factor-cleaving protease is not restricted to patients suffering from thrombotic thrombocytopenic purpura. Br J Haematol 2001; 112: 10878.
  • 107
    Moore JC, Hayward CP, Warkentin TE, Kelton JG. Willebrand factor protease activity associated with thrombocytopenic disorders. Blood 2001; 98: 18426.
  • 108
    Mannucci PM, Canciani MT, Forza I, Lussana F, Lattuada A, Rossi E. Changes in health and disease of the metalloprotease that cleaves von Willebrand factor. Blood 2001; 98: 27305.
  • 109
    Bianchi V, Robles R, Alberio L, Furlan M, Lämmle B. Von Willebrand factor-cleaving protease (ADAMTS-13) in thrombocytopenic disorders: a severely deficient activity is specific for thrombotic thrombocytopenic purpura. Blood 2002; 100: 7103.
  • 110
    Veyradier A, Obert B, Houllier A, Meyer D, Girma JP. Willebrand factor-cleaving protease in thrombotic microangiopathies: a study of 111 cases. Blood 2001; 98: 176572.
  • 111
    Mori Y, Wada H, Gabazza EC, Minami N, Nobori T, Shiku H, Yagi H, Ishizashi H, Matsumoto M, Fujimura Y. Predicting response to plasma exchange in patients with thrombotic thrombocytopenic purpura with measurement of vWF-cleaving protease activity. Transfusion 2002; 42: 57280.
  • 112
    Kremer Hovinga JA, Studt JD, Alberio L, Lämmle B. von Willebrand factor-cleaving protease (ADAMTS-13) activity determination in the diagnosis of thrombotic microangiopathies: the Swiss experience. Semin Hematol 2004; 41: 7582.
  • 113
    Matsumoto M, Yagi H, Ishizashi H, Wada H, Fujimura Y. The Japanese experience with thrombotic thrombocytopenic purpura-hemolytic uremic syndrome. Semin Hematol 2004; 41: 6874.
  • 114
    Zheng XL, Kaufman RM, Goodnough LT, Sadler JE. Effect of plasma exchange on plasma ADAMTS-13 metalloprotease activity, inhibitor level, and clinical outcome in patients with idiopathic and nonidiopathic thrombotic thrombocytopenic purpura. Blood 2004; 103: 40439.
  • 115
    Klaus C, Plaimauer B, Studt JD, Dorner F, Lämmle B, Mannucci PM, Scheiflinger F. Epitope mapping of ADAMTS-13 autoantibodies in acquired thrombotic thrombocytopenic purpura. Blood 2004; 103: 45149.
  • 116
    Raife T, Atkinson B, Montgomery R, Vesely S, Friedman K. Severe deficiency of VWF-cleaving protease (ADAMTS-13) activity defines a distinct population of thrombotic microangiopathy patients. Transfusion 2004; 44: 14650.
  • 117
    Langer F, Bergmann F, Budde U, Hegewisch-Becker S, Hossfeld DK. Prolonged inhibition of von Willebrand factor-cleaving protease after splenectomy in a 22-year-old patient with acute and plasma refractory thrombotic thrombocytopenic purpura. Br J Haematol 2002; 118: 2714.
  • 118
    Studt JD, Kremer Hovinga JA, Radonic R, Gasparovic V, Ivanovic D, Merkler M, Wirthmueller U, Dahinden C, Furlan M, Lämmle B. Familial acquired thrombotic thrombocytopenic purpura: ADAMTS-13 inhibitory autoantibodies in identical twins. Blood 2004; 103: 41957.
  • 119
    Kremer Hovinga JA, Studt JD, Demarmels Biasiutti F, Solenthaler M, Alberio L, Zwicky C, Fontana S, Mansouri Taleghani B, Tobler A, Lämmle B. Splenectomy in relapsing and plasma-refractory acquired thrombotic thrombocytopenic purpura. Haematologica 2004; 89: 3204.
  • 120
    van der Plas RM, Schiphorst ME, Huizinga EG, Hene RJ, Verdonck LF, Sixma JJ, Fijnheer R. von Willebrand factor proteolysis is deficient in classic, but not in bone marrow transplantation-associated, thrombotic thrombocytopenic purpura. Blood 1999; 93: 3798802.
  • 121
    Arai S, Allan C, Streiff M, Hutchins GM, Vogelsang GB, Tsai HM. Von Willebrand factor-cleaving protease activity and proteolysis of von Willebrand factor in bone marrow transplant-associated thrombotic microangiopathy. Hematol J 2001; 2: 2929.
  • 122
    Elliott MA, Nichols WL Jr, Plumhoff EA, Ansell SM, Dispenzieri A, Gastineau DA, Gertz MA, Inwards DJ, Lacy MQ, Micallef IN, Tefferi A, Litzow M. Posttransplantation thrombotic thrombocytopenic purpura: a single-center experience and a contemporary review. Mayo Clin Proc 2003; 78: 42130.
  • 123
    Fontana S, Gerritsen HE, Kremer Hovinga J, Furlan M, Lämmle B. Microangiopathic haemolytic anaemia in metastasizing malignant tumours is not associated with a severe deficiency of the von Willebrand factor-cleaving protease. Br J Haematol 2001; 113: 1002.
  • 124
    Tsai HM, Rice L, Sarode R, Chow TW, Moake JL. Antibody inhibitors to von Willebrand factor metalloproteinase and increased binding of von Willebrand factor to platelets in ticlopidine-associated thrombotic thrombocytopenic purpura. Ann Intern Med 2000; 132: 7949.
  • 125
    Bennett CL, Connors JM, Carwile JM, Moake JL, Bell WR, Tarantolo SR, McCarthy LJ, Sarode R, Hatfield AJ, Feldman MD, Davidson CJ, Tsai HM. Thrombotic thrombocytopenic purpura associated with clopidogrel. N Engl J Med 2000; 342: 17737.
  • 126
    Tsai HM, Chandler WL, Sarode R, Hoffman R, Jelacic S, Habeeb RL, Watkins SL, Wong CS, Williams GD, Tarr PI. von Willebrand factor and von Willebrand factor-cleaving metalloprotease activity in Escherichia coli O157:H7-associated hemolytic uremic syndrome. Pediatr Res 2001; 49: 6539.
  • 127
    Hunt BJ, Lämmle B, Nevard CH, Haycock GB, Furlan M. von Willebrand factor-cleaving protease in childhood diarrhoea-associated haemolytic uraemic syndrome. Thromb Haemost 2001; 85: 9758.
  • 128
    Török TJ, Holman RC, Chorba TL. Increasing mortality from thrombotic thrombocytopenic purpura in the United States – analysis of national mortality data, 1968–1991. Am J Hematol 1995; 50: 8490.
  • 129
    Terrell DR, Williams LA, Vesely SK, Lämmle B, Kremer Hovinga JA, George JN. The incidence of thrombotic thrombocytopenic purpura–hemolytic uremic syndrome: all patients, idiopathic patients, and patients with severe ADAMTS-13 deficiency. J Thromb Haemost 2005; in press.
  • 130
    Fontana S, Kremer Hovinga JA, Studt JD, Alberio L, Lämmle B, Mansouri Taleghani B. Plasma therapy in thrombotic thrombocytopenic purpura: review of the literature and the Bern experience in a subgroup of patients with severe acquired ADAMTS-13 deficiency. Semin Hematol 2004; 41: 4859.
  • 131
    Allford SL, Hunt BJ, Rose P, Machin SJ. Guidelines on the diagnosis and management of the thrombotic microangiopathic haemolytic anaemias. Br J Haematol 2003; 120: 55673.
  • 132
    Rock G, Shumak KH, Sutton DM, Buskard NA, Nair RC. Cryosupernatant as replacement fluid for plasma exchange in thrombotic thrombocytopenic purpura. Members of the Canadian Apheresis Group. Br J Haematol 1996; 94: 3836.
  • 133
    Zeigler ZR, Shadduck RK, Gryn JF, Rintels PB, George JN, Besa EC, Bodensteiner D, Silver B, Kramer RE. Cryoprecipitate poor plasma does not improve early response in primary adult thrombotic thrombocytopenic purpura (TTP). J Clin Apheresis 2001; 16: 1922.
  • 134
    Rock GA, Group TCA. Treatment of thrombotic thrombocytopenic purpura with plasma exchange using fresh frozen plasma or cryosupernatant plasma: variation in metalloprotease and vWF levels. 14th Congress of the European Society for Hemapheresis, September 10–13, 2003. Prague, Czech Republic, 2003.
  • 135
    Veltman GA, Brand A, Leeksma OC, ten Bosch GJ, van Krieken JH, Briet E. The role of splenectomy in the treatment of relapsing thrombotic thrombocytopenic purpura. Ann Hematol 1995; 70: 2316.
  • 136
    Crowther MA, Heddle N, Hayward CP, Warkentin T, Kelton JG. Splenectomy done during hematologic remission to prevent relapse in patients with thrombotic thrombocytopenic purpura. Ann Intern Med 1996; 125: 2946.
  • 137
    Aqui NA, Stein SH, Konkle BA, Abrams CS, Strobl FJ. Role of splenectomy in patients with refractory or relapsed thrombotic thrombocytopenic purpura. J Clin Apheresis 2003; 18: 514.
  • 138
    Gutterman LA, Kloster B, Tsai HM. Rituximab therapy for refractory thrombotic thrombocytopenic purpura. Blood Cells Mol Dis 2002; 28: 38591.
  • 139
    Chemnitz J, Draube A, Scheid C, Staib P, Schulz A, Diehl V, Sohngen D. Successful treatment of severe thrombotic thrombocytopenic purpura with the monoclonal antibody rituximab. Am J Hematol 2002; 71: 1058.
  • 140
    Zheng X, Pallera AM, Goodnough LT, Sadler JE, Blinder MA. Remission of chronic thrombotic thrombocytopenic purpura after treatment with cyclophosphamide and rituximab. Ann Intern Med 2003; 138: 1058.
  • 141
    Tsai HM, Shulman K. Rituximab induces remission of cerebral ischemia caused by thrombotic thrombocytopenic purpura. Eur J Haematol 2003; 70: 1835.
  • 142
    Ahmad A, Aggarwal A, Sharma D, Dave HP, Kinsella V, Rick ME, Schechter GP. Rituximab for treatment of refractory/relapsing thrombotic thrombocytopenic purpura (TTP). Am J Hematol 2004; 77: 1716.
  • 143
    Sallah S, Husain A, Wan JY, Nguyen NP. Rituximab in patients with refractory thrombotic thrombocytopenic purpura. J Thromb Haemost 2004; 2: 8346.
  • 144
    Furlan M, Robles R, Morselli B, Sandoz P, Lämmle B. Recovery and half-life of von Willebrand factor-cleaving protease after plasma therapy in patients with thrombotic thrombocytopenic purpura. Thromb Haemost 1999; 81: 813.
  • 145
    Dundas S, Murphy J, Soutar RL, Jones GA, Hutchinson SJ, Todd WT. Effectiveness of therapeutic plasma exchange in the 1996 Lanarkshire Escherichia coli O157:H7 outbreak. Lancet 1999; 354: 132730.
  • 146
    Chandler WL, Jelacic S, Boster DR, Ciol MA, Williams GD, Watkins SL, Igarashi T, Tarr PI. Prothrombotic coagulation abnormalities preceding the hemolytic-uremic syndrome. N Engl J Med 2002; 346: 2332.
  • 147
    Raife T, Friedman KD, Fenwick B. Lepirudin prevents lethal effects of Shiga toxin in a canine model. Thromb Haemost 2004; 92: 38793.
  • 148
    Pichette V, Querin S, Schurch W, Brun G, Lehner-Netsch G, Delage JM. Familial hemolytic-uremic syndrome and homozygous factor H deficiency. Am J Kidney Dis 1994; 24: 93641.
  • 149
    Warwicker P, Goodship TH, Donne RL, Pirson Y, Nicholls A, Ward RM, Turnpenny P, Goodship JA. Genetic studies into inherited and sporadic hemolytic uremic syndrome. Kidney Int 1998; 53: 83644.
  • 150
    Rougier N, Kazatchkine MD, Rougier JP, Fremeaux-Bacchi V, Blouin J, Deschenes G, Soto B, Baudouin V, Pautard B, Proesmans W, Weiss E, Weiss L. Human complement factor H deficiency associated with hemolytic uremic syndrome. J Am Soc Nephrol 1998; 9: 231826.
  • 151
    Noris M, Ruggenenti P, Perna A, Orisio S, Caprioli J, Skerka C, Vasile B, Zipfel PF, Remuzzi G. Hypocomplementemia discloses genetic predisposition to hemolytic uremic syndrome and thrombotic thrombocytopenic purpura: role of factor H abnormalities. Italian Registry of Familial and Recurrent Hemolytic Uremic Syndrome/Thrombotic Thrombocytopenic Purpura. J Am Soc Nephrol 1999; 10: 28193.
  • 152
    Taylor CM. Hemolytic-uremic syndrome and complement factor H deficiency: clinical aspects. Semin Thromb Hemost 2001; 27: 18590.
  • 153
    Lesesve JF, Salignac S, Alla F, Defente M, Benbih M, Bordigoni P, Lecompte T. Comparative evaluation of schistocyte counting by an automated method and by microscopic determination. Am J Clin Pathol 2004; 121: 73945.
  • 154
    Takahashi H, Tatewaki W, Wada K, Shibata A. Thrombin generation in patients with thrombotic thrombocytopenic purpura. Am J Hematol 1989; 32: 2557.