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To study both the pathophysiologic and the prognostic value of ADAMTS13 in thrombotic microangiopathies (TMAs), we enrolled a cohort of 35 adult patients combining a first acute episode of TMA, an undetectable (below 5%) ADAMTS13 activity in plasma, and no clinical background such as sepsis, cancer, HIV, and transplantation. All patients were treated by steroids and plasma exchange, and an 18-month follow-up was scheduled. Remission was obtained in 32 patients (91.4%), and 3 patients died (8.6%) after the first attack. At presentation, ADAMTS13 antigen was decreased in 32 patients (91.4%), an ADAMTS13 inhibitor was detectable in 31 patients (89%), and an anti-ADAMTS13 IgG/IgM/IgA was present in 33 patients (94%). The 3 decedent patients were characterized by the association of several anti-ADAMTS13 Ig isotypes, including very high IgA titers, while mortality was independent of the ADAMTS13 inhibitor titer. In survivors, ADAMTS13 activity in remission increased to levels above 15% in 19 patients (59%) but remained undetectable in 13 patients (41%). Six patients relapsed either once or twice (19%) during the follow-up. High levels of inhibitory anti-ADAMTS13 IgG at presentation were associated with the persistence of an undetectable ADAMTS13 activity in remission, the latter being predictive for relapses within an 18-month delay. IntroductionThrombotic microangiopathies (TMAs) are defined by the association of acute mechanical hemolytic anemia, thrombocytopenia, and visceral ischemic manifestations related to the formation of platelet thrombi in the microcirculation. 1 Clinically, TMA includes mainly the thrombotic thrombocytopenic purpura (TTP) and the hemolytic uremic syndrome (HUS) characterized by a multivisceral ischemia and a renal ischemia, respectively. 2 Although mechanisms for HUS remain very heterogeneous, pathophysiology for most forms of TTP is related to a severe deficiency of a plasma metalloprotease, ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats). [3][4][5][6] Physiologically, ADAMTS13 is the specific cleaving protease for von Willebrand factor (VWF), a large multimeric glycoprotein crucial for both platelet adhesion and aggregation in the high stress-associated hemodynamic conditions of the microcirculation. 7 A severe enzymatic deficiency of ADAMTS13 causes highly adhesive unusually large multimers of VWF to accumulate in plasma, which may spontaneously bind to platelets and thus induce the formation of platelet thrombi in the microcirculation. In rare cases, clinically relevant ADAMTS13 severe deficiency is related to compound heterozygous or homozygous mutations of the ADAMTS13 gene (Upshaw-Schulman syndrome). [8][9][10] In most cases, severe ADAMTS13 deficiency is secondary to the development of anti-ADAMTS13 autoantibodies (auto-Abs). [11][12] Anti-ADAMTS13 auto-Abs can be detected in vitro either functionally because of their inhibitory effect on ADAMTS13 enzymatic activity [13][14] or, more recently, physically as immunoglobulin G (IgG) or IgM by enzyme-lin...

An as yet single family with a bleeding history is shown to present the characteristic lack of membrane expression of procoagulant phospholipids observed in Scott syndrome. Low prothrombin consumption in the serum of the propositus, a 71-year-old woman, and two of her children was the sole abnormal hemostasis parameter. The degree of exposure of procoagulant phospholipids, chiefly phosphatidylserine, was reduced in stimulated platelets, erythrocytes and Epstein-Barr virus- infected B lymphocytes. The data are compatible with homozygous status of the propositus and heterozygous status of her children. Scott syndrome appears to be transmitted as an autosomal recessive trait reflecting the deletion or mutation of a putative outward phosphatidylserine translocase. The detailed knowledge of this transporter could have an impact in membrane physiology.

A new variant of von Willebrand disease (vWD) was identified by a new analytic method which characterizes the ability of plasma von Willebrand Factor (vWF) to bind to purified factor VIII (F.VIII). vWF was isolated from small amounts of plasma by immunoadsorption with a selected monoclonal antibody to vWF previously coated onto wells of microtitration plates. Plasma F.VIII was removed from immobilized vWF by washing with 0.4 mol/L CaCl2; purified F.VIII was then added to the well. The amount of bound F.VIII was estimated directly in the wells by a chromogenic assay and immobilized vWF was estimated by an immunologic a pool of normal plasma, ten control individuals, 13 with hemophilia A and five with type I vWD. In all cases, the dose-response curves were linear and the slopes of the regression lines were essentially the same. The method was then applied to investigate the binding of vWF to F.VIII in two vWD patients (sister and brother) who demonstrated significantly lower activity of F.VIII than of vWF. The first patient, with a long history of epistaxis, bruising, and hematomas, showed a slightly prolonged bleeding time (10 minutes); 15% VIII:C and 39% of vWF:Ag and vWFRCo. Her brother, who has a bleeding syndrome but no hematomas, showed similar data (bleeding time 9 minutes, 20% VIII:C, 53% vWF:Ag and vWFRCo). Similar levels of F.VIII were observed in the two propositi by four different methods (one- and two-stage clotting and chromogenic and immunologic assays). Sodium dodecyl sulfate (SDS) 1.4% agarose gel electrophoresis showed that all multimers of vWF were present in both patients. vWF binding to F.VIII was markedly decreased in the two propositi. The abnormal binding of vWF to F.VIII was not corrected during pregnancy or after infusion of 1-deamino (8-D- arginine) vasopressin despite an increase in vWF levels. The qualitative abnormality of vWF in both patients was associated with a subtle alteration of the multimeric structure by SDS 3% agarose gel electrophoresis in which the two central subbands of the quintuplet of individual oligomers were undetectable or poorly visible. SDS- polyacrylamide gel electrophoresis under reducing conditions demonstrated a single band of 275 Kd in the plasma of both patients, and there was no evidence of a second band corresponding to pro-vWF, the precursor of the mature vWF subunit, suggesting that proteolytic processing of vWF was normal.

SummaryA protease present in plasma cleaves von Willebrand factor (vWF) at the peptide bond 842Tyr-843Met of the mature subunit. To quantify this vWF-cleaving protease activity in plasma we have developed a simple method based on the estimation by IRMA of the degradation of a constant amount of wild type recombinant vWF used as substrate, by serial dilutions of test plasma used as protease provider. vWFAg was estimated by two-site IRMA using as first coating antibody a monoclonal antibody (MoAb) whose epitope is localized on the C-terminal side of the cleavage site, and as second labeled antibody a pool of MoAbs specific for the N-terminal side. Because the proteolytic process leads to the progressive separation of the C- and N-terminal portions of the vWF subunit such an IRMA also shows a progressive apparent loss of vWFAg. In contrast, the levels of vWFAg estimated after proteolysis by regular IRMA remained essentially constant. Results obtained with this new method were compared with the analysis by SDS-agarose gel electrophoresis of the multimeric pattern of proteolyzed WT-rvWF and no significant difference was noted testing a series of 28 plasmas. As compared with normal pooled plasma, 14 normal individuals and 13 patients with various types of vWD had normal levels of protease activity (44-178%) by both methods. The validity of the method was confirmed by showing a lack of detectable protease activity in a patient with chronic relapsing thrombotic thrombocytopenic purpura. In conclusion our method appears as a useful tool for the quantification of the vWF-cleaving protease activity in plasma. Its sensitivity and specificity are similar to those of SDS-gel electrophoresis. However, this new IRMA has the major advantages of being much simpler and faster, and open to most research laboratories in the field.