Severe Deficiency Of ADAMTS13 Activity Research Articles

Paradigm shift of childhood thrombotic thrombocytopenic purpura with severe ADAMTS13 deficiency

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening generalized disease with pathological conditions termed thrombotic microangiopathy (TMA). TTP is thought to predominantly affect adults and to rarely occur in children. Currently, TTP is defined by a severe deficiency in the activity of ADAMTS13, a metalloprotease that specifically cleaves unusually large von Willebrand factor multimers under high shear stress. Genetic mutations in and acquired autoantibodies to ADAMTS13 cause congenital TTP (termed Upshaw-Schulman syndrome [USS]) and acquired TTP, respectively. Because of very few overt clinical signs for TTP, USS is often misdiagnosed as chronic idiopathic thrombocytopenic purpura or overlooked during childhood. However, in women with USS, pregnancy can induce thrombocytopenia followed by the development of TTP. Furthermore, early childhood cases of acquired idiopathic TTP have not been characterized. From 1998 to 2008, our institution at Nara Medical University functioned as a TMA referral center in Japan and collected a large dataset on 919 TMA patients (Intern Med 2010;49:7-15). This registry contains 324 patients with a severe deficiency in ADAMTS13 activity, including 41 patients with USS and 283 patients with acquired TTP. Of note, the latter population contains 17 patients who were enrolled as children (≤ 15years old), including 14 children with idiopathic TTP and three with connective tissue disease-associated TTP. Of the 14 patients with idiopathic TTP, five were very young children (under 2 years old). This study focused on these 58 patients (41 USS and 17 acquired TTP) who were diagnosed with a severe deficiency in ADAMTS13 activity during childhood, causing a paradigm shift in our concept of TTP.

A Large-Pore IEF Gel Electrophoresis Separates the Complex in Both of ADAMTS13 Bound to VWF and to the IgG Autoantibodies From the Unbound in Plasma Milieu

Abstract 1160 Backgrounds and Aims:Thrombotic thrombocytopenic purpura (TTP) is a life-threatening generalized disorder caused by a deficiency of ADAMTS13 activity due to its gene mutations (Upshaw-Schulman syndrome), and/or acquired autoantibodies to this enzyme. ADAMTS13 specifically cleaves the peptide bond between Tyr1605 and Met1606 within the A2 domain of von Willebrand factor (VWF). Recent studies with immunoprecipitation methods using anti-VWF antibody coated beads indicated that a small portion (3–4% of the total) of plasma ADAMTS13 is bound to VWF (Feys HB et al. JTH 7:2088, 2009). This experiment determined the amount of ADAMTS13 bound to VWF in an indirect fashion, but the complex may dissociate during washing procedures or by conformation change after binding to the antibody. Thus, we used an isoelectric focusing (IEF) to separate the complex in a direct fashion. However, the molecular size of VWF-ADAMTS13 complex is assumed to be enormously huge, and therefore a regular polyacrylamide IEF gel does not properly work. So, we employed a large-pore composite IEF gel consisting 0.75% agarose and 1.25% polyacrylamide containing 2% of Pharmalyte (pI range 3.0–10). By this method followed by western blot detection using a non-neutralizing anti-ADAMTS13 monoclonal antibody (WH2-11-1), we identified that an ADAMTS13-VWF complex is detected as a sharp band at pI 7.4. The specificity of this band was identified by a lack in plasma of type 3 von Willebrand disease (VWD), and a new emergence of the band in type 3 VWD plasma spiked with purified VWF (Hori et al, 57th ISTH meeting, P-MO-479). We applied this IEF analysis to detect the complex of ADAMTS13-its autoantibodies. Patients and Methods:ADAMTS13 activity was measured by chromogenic act-ELISA, and acquired idiopathic (ai-) TTP with severe deficiency of ADAMTS13 activity due the presence of its autoantibodies is a target in this study. VWF and ADAMTS13 were purified from normal plasma. A large-pore composite IEF gel electrophoresis was performed as previously described. Results and Discussion:Two forms of ADAMTS13, unbound (pI 5.3) and bound (pI 7.4) to VWF in a volume of 10 uL normal plasma (NP), were directly identified on the IEF gel followed by western blotting (Fig. left). Each plasma of type 3 VWD or USS lacked the complex (VWF-ADAMTS13) band with pI 7.4, but it was generated in vitro just after spiking the purified VWF or ADAMTS13 to the respective deficient plasma by the IEF (Fig. not shown). [Display omitted] Next, when a volume of 3uL NP was analyzed, only one band with pI of 5.3 (5.1–5.5) was observed. In ai-TTP patients with severe deficiency of ADAMTS13 activity (<3% of the control), plasma had no or faint band of ADAMTS13 (Fig. middle). However, when we mixed the equal volume of patient plasma with ai-TTP with severe deficiency of ADAMTS13 activity and NP, the results on IEF gel showed appearance of 3 major bands with pIs of 5.3, 5.9 and 6.5, together with other many minor bands, and the unbound (free) ADAMTS13 almost disappeared (Fig. right). Then, the IgG purified from patient plasma of ai-TTP was mixed with NP or purified ADAMTS13, the complex band had a pI of 5.9 (5.5–6.3). These results indicated a possibility that the IEF analysis could be used to detect the autoantibodies to ADAMTS13, regardless of the neutralizing or non-neutralizing counterparts, in a totally different fashion to the enzyme immunoassay. Disclosures:Matsumoto:Alexion Pharma: Membership on an entity's Board of Directors or advisory committees. Soejima:The Chemo-Sero-Therapeutic Research Institute: Employment. Fujimura:Baxter BioScience: Membership on an entity's Board of Directors or advisory committees; Alexion Pharma: Membership on an entity's Board of Directors or advisory committees.

Thrombotic thrombocytopenic purpura in IgG4‐related disease with severe deficiency of ADAMTS‐13 activity and IgG4 autoantibody against ADAMTS‐13

IgG4-related disease is a recently recognized group characterized by elevated serum IgG4 levels and prominent lymphoplasmacytic infiltration of IgG4-positive cells into multiple organs (1). The condition was first described in relation to the pancreas (i.e., autoimmune pancreatitis [AIP] [2]), but since then many other inflammatory conditions associated with IgG4-related disease have been reported, including sclerosing cholangitis, sialadenitis, lymphadenopathy, retroperitoneal fibrosis, interstitial pneumonia, and tubulointerstitial nephritis (1,3,4). Laboratory findings in IgG4-related disease are commonly characterized by hypergammaglobulinemia and high levels of serum IgG and IgG4, and in addition, a high serum IgE level, peripheral eosinophilia, and hypocomplementemia are often observed (3,4). Thrombocytopenia in IgG4-related disease is rare, but a few cases of autoimmune thrombocytopenia have been reported in patients with AIP (5,6). We describe here, to our knowledge, the first case of acquired thrombotic thrombocytopenic purpura (TTP) in a patient with IgG4-related lung disease with severe deficiency of ADAMTS-13 activity and IgG4 autoantibody against ADAMTS-13.

A 9-MONTH-OLD INFANT WITH ACQUIRED IDIOPATHIC THROMBOTIC THROMBOCYTOPENIC PURPURA CAUSED BY INHIBITORY IgG-AUTOANTIBODY TO ADAMTS13

Although acquired idiopathic thrombotic thrombocytopenic purpura (ai-TTP) is rare in children, the authors present the case of a 9-month-old boy with ai-TTP showing severe deficiency of ADAMTS13 activity by its inhibitory IgG-autoantibody (4.8 Bethesda units/mL). Plasma exchange therapy was clinically effective but transient. Deficient activity of ADAMTS13 with the presence of its inhibitor persisted for 7 months after the initial diagnosis. However, other laboratory findings improved gradually with steroid (pulse) therapy. The hitherto insufficiently characterized clinical settings of ai-TTP during early childhood underscore the importance of measuring ADAMTS13 activity and its inhibitors for differential diagnosis in patients with thrombocytopenia of unknown etiology.

Evaluation and Clinical Application of a New Method for Detecting ADAMTS13 Activity.

Abstract 2134Poster Board II-111 Introduction:A severe deficiency of ADAMTS13 activity contributes to the pathogenesis of thrombotic thrombocytopenic purpura (TTP). Measuring the activity of ADAMTS13 is helpful for the diagnosis of TTP and the prognostic monitor in TTP patients. Most available assays are cumbersome and costly, and not appropriate for routine laboratories. ADAMTS13 cleaves the von Willebrand factor (VWF) within the domain A2, which locates between the domains A1 and A3. Therefore, specific assays for ADAMTS13 activity could be based on the different structure of VWF before and after the cleavage. Materials and Methods:To determine the activity of ADAMTS13, a new simple method has been developed in this study. Firstly, plasma samples were exposed in denaturing condition to allow cleavage of VWF by ADAMTS13. Then, the ADAMTS13 activity was measured with two novel monoclonal antibodies (SZ-129 and SZ-125), which are specifically recognize the VWF A1 and A3 domain, respectively, by using a two-site sandwich ELISA. Comparing with a residual-collagen binding assay (R-CBA), plasma ADAMTS13 activities in 161 samples were assessed, and the inhibitory activities of ADAMTS13 autoantibodies in 24 TTP patients were determined. The relationship of these two assays was analyzed by linear correlation, and the sensitivity and specificity of the new assay was also evaluated. ResultsOur results showed that plasma ADAMTS13 activities determined by the new assay were consistent with those of R-CBA, the squared correlation factor was 0.9183 of the two assays, and the coefficient of variation for the new assay was 6.17%. In 23 idiopathic TTP patients, the inhibitor activities of ADAMTS13 autoantibodies were ranged from 12% to 100%, while no inhibitory activity was detected in one hereditary TTP patient. ConclusionsThis new and simple assay for ADAMTS13 activity could be used routinely in clinic to determine the activity of ADAMTS13. Disclosures:No relevant conflicts of interest to declare.

Heterogeneous pathogenic processes of thrombotic microangiopathies in patients with connective tissue diseases

To clarify the pathogenic processes of thrombotic microangiopathies (TMAs) in patients with connective tissue disease (CTD), we analysed clinical characteristics and plasma ADAMTS13 levels in 127 patients with CTD-TMAs, including patients with systemic lupus erythematosus (SLE), systemic sclerosis, polymyositis/dermatomyositis, and rheumatoid arthritis (RA), and 64 patients with acquired idiopathic thrombotic thrombocytopenic purpura (ai-TTP). Plasma levels of ADAMTS13 activity, antigen, and inhibitors were determined by enzyme immunoassays. IgG type anti-ADAMTS13 antibodies were also detected by immunoblots using purified ADAMTS13. ADAMTS13 activity was significantly decreased in CTD-TMAs, regardless of the underlying disease, but the frequency of severe deficiency (defined as <0.5% of normal) was lower in CTD-TMA patients than in ai-TTP patients (16.5% vs. 70.3%, p < 0.01). Severe deficiency of ADAMTS13 activity was predominantly detected in patients with RA- and SLE-TMAs, and was closely associated with the presence of anti-ADAMTS13 IgG antibodies. CTD-TMA patients with severe deficiency of ADAMTS13 activity appeared to have lower platelet counts and better therapeutic outcomes. At least two phenotypic TMAs occur in patients with CTDs: a minor population with deficient ADAMTS13 activity caused by neutralising autoantibodies, and a major population with normal or moderately reduced activity. Classifying CTD-TMAs by ADAMTS13 activity may be useful in predicting the clinical course and therapeutic outcomes, as patients with moderately reduced activity are likely to have more prominent renal impairment and poor prognoses.

Chemotherapy-resistant intravascular lymphoma accompanied by ADAMTS13 inhibitor successfully treated with rituximab

Intravascular large B-cell lymphoma (IVL) is a subtype of diffuse large B-cell lymphoma (DLBCL), in which lymphoma cells infiltrate blood vessels without mass formation, and its prognosis is generally poor due to diagnostic difficulties. The authors previously described a patient with IVL accompanied by features of thrombotic thrombocytopenic purpura (TTP), expression of ADAMTS13 inhibitor, and a severe deficiency in ADAMTS13 activity [1]. Although standard CHOP chemotherapy was initially effective, the disease gradually became resistant despite intensive high-dose chemotherapy with autologous peripheral blood stem cell support. However, the chimeric anti-CD20 monoclonal antibody, rituximab, induced complete remission (CR) for a prolonged period. We describe the clinical course of this patient and the unique effects of treatment with rituximab alone. A 54-year-old man was admitted to our hospital with the onset of a psychological disorder and convulsions. Laboratory data revealed obvious thrombocytopenia (3.6 9 10/ lL) accompanied by elevated levels of serum lactic dehydrogenase (LDH) and soluble interleukin-2 receptor. Multiple cerebral venous embolisms, bilateral adrenal gland swelling, and hepatosplenomegaly were present without nodal disease. Despite normal chest X-rays and thoracic CT scans, the patient developed rapidly progressive respiratory failure. A definitive diagnosis of IVL was made from transbronchial lung biopsy (TBLB) specimens. Bone marrow smears revealed no obvious lymphoma cell invasion and megakaryocyte hyperplasia without hemophagocytic syndrome (HPS), although the peripheral blood platelet count was markedly decreased. We concluded that the thrombocytopenia was caused by the same pathogenesis as TTP, since plasma ADAMTS13 activity had decreased to below 3%, and active ADAMTS13 inhibitor (IgG-type autoantibody) was confirmed. After standard CHOP chemotherapy cycles, the platelet counts immediately recovered to within normal limits and all symptoms improved. The ADAMTS13 activity improved to 49% and inhibitor levels, which had never been negative, decreased. Whole brain irradiation after chemotherapy resulted in relapse of systemic disease. Although we performed highdose conditioning chemotherapy followed by autologous peripheral stem cell transplantation, respiratory failure and high-grade fever appeared with severe thrombocytopenia and massive serum LDH elevation at day 50 after transplantation. Salvage combination chemotherapies had extremely limited effects against the disease, and we started to administer 375 mg/m of rituximab after its use for CD20-positive DLBCL was permitted according to the regulations established by the Japanese National Health Insurance system. The patient did not develop any major M. Kanno (&) Tumor Center, Nara Medical University Hospital, 840 Shijo-cho, Kashihara 634-8522, Japan e-mail: mkanno@naramed-u.ac.jp

ADAMTS13 and anti-ADAMTS13 antibodies as markers for recurrence of acquired thrombotic thrombocytopenic purpura during remission

From 20 to 50% of patients who survive an acute episode of the acquired form of thrombotic thrombocytopenic purpura relapse but clinical and laboratory markers of recurrence are not well established. In 109 patients enrolled in an international registry we evaluated, in the frame of a retrospective cohort study, the predictive role of the metalloprotease ADAMTS13 as measured in plasma during remission. Anti-ADAMTS13 antibodies and von Willebrand factor were also evaluated in a smaller number of the same patients. Median values of ADAMTS13 activity and antigen were significantly lower in patients with recurrent thrombotic thrombocytopenic purpura than in those with no recurrence (activity: 12% vs. 41%; p=0.007; antigen: 36% vs. 58%; p=0.003). A severe deficiency of ADAMTS13 activity (10% or less) was associated with a higher likelihood of recurrence (odds ratio 2.9; 95% confidence interval 1.3 to 6.8; p=0.01). Anti-ADAMTS13 antibodies were also more prevalent in patients with recurrent thrombotic thrombocytopenic purpura (odds ratio 3.1; 95% confidence interval 1.4 to 7.3; p=0.006). The presence during remission of both severe ADAMTS13 deficiency and anti-ADAMTS13 antibodies increased the likelihood of recurrence 3.6 times (95% confidence interval 1.4 to 9.0; p=0.006). The presence of ultralarge von Willebrand factor multimers and of associated diseases or conditions did not increase recurrence. Survivors of an acute episode of acquired thrombotic thrombocytopenic purpura with severely reduced levels of ADAMTS13 and/or with anti-ADAMTS13 antibodies during remission have an approximately three-fold greater likelihood of developing another episode of thrombotic thrombocytopenic purpura than patients with higher protease activity and no antibody.

Pronounced Reduction in ADAMTS13 Activity Occurs in Heparin Induced Thrombocytopenia but Is Not Due to IgG ANTI-ADAMTS13.

Although severe deficiency in ADAMTS13 activity (<5%) can result in the development of thrombotic thrombocytopenic purpura (TTP), a less marked reduction in ADAMTS13 occurs in the acute phase reaction of sepsis and DIC, and may promote thrombosis in various disease states. Heparin induced thrombocytopenia (HIT) shares many important similarities with TTP. Both are autoimmune prothrombotic disorders characterised by pathogenic antibodies, marked endothelial cell activation, thrombocytopenia, and the development of thrombosis. ADAMTS13 parameters in HIT have not been well characterised and there is no consensus on the severity of the reduction in ADAMTS13 activity. We hypothesize that a pronounced reduction in ADAMTS13 activity can occur in HIT and investigated potential mechanisms underlying ADAMTS13 depletion. We evaluated ADAMTS13 activity, anti-ADAMTS13 IgG and VWF:Ag in double-spun citrated plasma from 20 patients (median age 64, Male:Female = 14:6). 15 were HIT positive (of whom 10 were cardiothoracic cases) and 5 were suspected HIT thrombocytopenic cases, but HIT negative. HIT antibodies were measured by ELISA (either: PF4 enhanced, GTI Diagnostics; or Asserachrom HPIA, Diagnostica Stago) and platelet aggregation (heparin dependence was demonstrated using a known responder as the platelet donor). ADAMTS13 activity was determined by a modified residual collagen binding assay, and anti-ADAMTS13 IgG by an in-house ELISA using recombinant ADAMTS13-coated microtitre plates. VWF:Ag was measured using an immunoturbidimetric assay (Dade Behring). The median HIT antibody concentration in the 15 HIT cases was 1.57 OD using PF4-enhanced ELISA (range 0.91–2.44), and 143% using HPIA (range 69–181%). The median platelet nadir was 57×109/L (range 6–132×109/L). ADAMTS13 activity (normal range (NR): 66–126%) was reduced in 15/15 (100%) HIT positive patients (median 17%, range 0–55%), but also in 4/5 (80%) HIT negative thrombocytopenic patients (median 31%, range 18–76%). There was no statistically significant difference between these two groups (p=0.12). Furthermore, the ADAMTS13 activity of the 10 cardiothoracic patients was not significantly different from the remaining HIT positive cases. Anti-ADAMTS13 IgG was detected in 3/15 HIT positive patients (with IgG levels of 12%, 28% and 69% [NR <4%]) and 1/5 HIT negative cases (IgG of 21%). VWF:Ag was elevated (>200 iu/dL) in 18/20 with a median VWF:Ag of 297 iu/dL (range 165–606 iu/dL). These observations show that ADAMTS13 activity is often low in HIT patients, and can be markedly reduced in some cases. However, ADAMTS13 IgG autoantibodies were only detected in 3 cases, suggesting that autoantibody production is not the predominant mechanism for reduced ADAMTS13 function. The high VWF:Ag observed in HIT is an acute phase reactant and represents excess ADAMTS13 substrate, which drives the process of VWF proteolysis and causes circulating ADAMTS13 depletion. This may ultimately promote the prothrombotic milieu seen in HIT.

Ticlopidine- and Clopidogrel-Associated Thrombotic Thrombocytopenic Purpura (TTP): Final Results from the Surveillance Epidemiology and Risk Factor-TTP Study Group.

Thrombotic thrombocytopenic purpura (TTP) is a microvascular occlusive disorder characterized by systemic aggregation of platelets, thrombocytopenia, and mechanical injury to erythrocytes. Between 30% and 80% of TTP cases are associated with ADAMTS13 deficiency. Thienopyridine-derivative anti-platelet agents, ticlopidine and clopidogrel, are the drugs most commonly associated with TTP. The structures differ only by a carboxymethyl side-chain and have no common metabolites. Since 2002, our R01 research project has focused on evaluating thienopyridine-associated TTP. Herein, we present the final results. Clinical and laboratory data were obtained from case reports, the FDA's MedWatch program, a Japanese national reference laboratory for ADAMTS13 assays, and apheresis centers at Duke University, University of North Carolina, Northwestern University, and the Mayo Clinic. Epidemiologic data for rate estimation for thienopyridine-associated TTP among persons who receive cardiac stents were obtained from international cardiology laboratories. Pharmacovigilance information was obtained from package inserts for the drugs. Most thienopyridine-associated TTP cases are associated with two weeks or more of ticlopidine rather than clopidogrel, are immune-mediated involving neutralizing antibodies to ADAMTS13, resolve with therapeutic plasma exchange (TPE), and have spontaneous relapses. Less frequently, cases are associated with clopidogrel, occur within days of drug initiation, may be a direct result of endothelial cell damage, are less responsive to TPE, and are less likely to recur. Thienopyridine-associated TTP patients with severe deficiency of ADAMTS13 activity have a different profile than those with normal ADAMTS13 levels. Among thienopyridine-associated TTP patients who have ADAMTS13 deficiency, TPE is usually performed for a few days and patients recover without detectable organ damage. In contrast, among thienopyridine-associated TTP patients who do not have ADAMTS13 deficiency, several weeks of TPE is required for recovery, and 30% mortality rates have been reported. Despite similar chemical structures, ticlopidine- and clopidogrel-associated TTP probably occur by different mechanisms and have different clinical presentations and expected outcomes.Clinical CharacteristicsOnsetPlatelet Count <20,000 (%)Creatinine ≤2 mg/dl (%)Neurologic Symptoms (%)Mortality With TPE/Without TPE (%)Relapseticlopidine10%* <2 weeks; 90% 2-12 weeks84*28*2815/44Occasionalclopidogrel74%*≤2 weeks; 26% > 2 weeks60*55*3228/33RareEpidemiology, Pharmacovigilance & Basic ScienceIncidence (cases per treated patients)SafetyADAMTS13 Activity (%)ADAMTS13 Antibodies (%)ticlopidine1:1,600“Black Box” warning<10*90*clopidogrel1:100,000package insert warning50–100*10**p < 0.05

Are There Two Distinct Mechanistic Pathways That Explain the Varying Clinical Presentations, Laboratory Findings, and Outcomes of Thienopyridine-Associated Thrombotic Thrombocytopenic Purpura (TTP)?.

Introduction: The antiplatelet agents ticlopidine and clopidogrel are thienopyridine derivatives that are commonly used for secondary prevention of cerebrovascular events, prevention of coronary artery stent thrombosis, and for treatment of acute coronary syndrome. While these chemically related agents are the first and third most common causes of drug-associated TTP respectively, clinical presentations, laboratory findings, and outcomes suggest that there may be two distinct mechanistic pathways.Methods: Clinical and laboratory data for 60 cases of ticlopidine-associated TTP and 35 cases of clopidogrel associated TTP were reviewed.Results: Type 1 thienopyridine-associated TTP, characterized by onset of disease > 5 days after drug initiation, occurred in 98% of the ticlopidine patients versus 63% of the clopidogrel patients. Laboratory studies identified severe deficiency of ADAMTS13 activity and the presence of IgG inhibitors in 7 ticlopidine (Tsai, et al.; Annals of Internal Medicine, 2000) and 2 clopidogrel (Bennett, et al.; NEJM, 2000) patients. Survival was 68% in the ticlopidine patients versus 91% in the clopidogrel patients. Type 2 thienopyridine-associated TTP, consisting of TTP onset within 5 days of drug initiation, occurred in 2% of the ticlopidine patients versus 37% of the clopidogrel patients. Laboratory studies failed to identify deficient ADAMTS13 activity or the presence of IgG inhibitors in 1 clopidogrel patient (Zheng, et al.; Blood, 2004). Survival was 0% in the ticlopidine patients versus 38% in the clopidogrel patients.Conclusion: The proposed type 1 and type 2 thienopyridine-associated TTP may be distinguished on the basis of clinical presentation, ADAMTS13 levels, and outcome. Type 1 thienopyridine-associated TTP—characterized as occurring after > 5 days of thienopyridine treatment, severely deficient ADAMTS13 activity and presence of IgG inhibitors, and high survival rates with plasmapheresis—is more likely to occur in patients receiving ticlopidine. Type 2 thienopyridine-associated TTP—characterized as occurring within 5 days of thienopyridine therapy initiation, normal ADAMTS13 activity and undetectable IgG inhibitors, and poor survival rates despite plasmapheresis—is more likely to occur in patients receiving clopidogrel. Additional confirmatory studies on larger numbers of patients are needed.

Severe deficiency of VWF-cleaving protease (ADAMTS13) activity defines a distinct population of thrombotic microangiopathy patients.

Severe deficiency of ADAMTS13 activity is a biologic risk factor for thrombotic microangiopathy (TMA). It was hypothesized that severe ADAMTS13 deficiency is associated with a distinct TMA subpopulation. ADAMTS13 activity before treatment was determined retrospectively in 107 adult TMA patients treated with plasma exchange. Patients were not clinically categorized, but divided between severely deficient (n = 50) and nonseverely deficient (n = 57) ADAMTS13 activity. Laboratory and clinical factors before treatment were compared between the groups. Median PLT counts were 44,000 per micro L in nonseverely deficient ADAMTS13 patients and 13,000 per micro L in severely deficient ADAMTS13 patients (p < 0.001). Median serum creatinine levels were 2.7 mg per dL in nonseverely deficient patients and 1.2 mg per dL in severely deficient patients (p < 0.001). In surviving patients, median plasma exchange procedures were 9 in nonseverely deficient patients and 14.5 in severely deficient patients (p < 0.01). Rates of relapse following remission were 4 of 47 in nonseverely deficient patients and 16 of 46 in severely deficient patients (p < 0.01). Among analyzed factors only mortality rates were not significantly different. In a heterogeneous population of TMA patients treated with plasma exchange, ADAMTS13 activity defined two subpopulations with distinct clinical and laboratory features. These results suggest that TMA with severe ADAMTS13 deficiency is a distinct pathologic process.

Nonneutralizing IgM and IgG antibodies to von Willebrand factor–cleaving protease (ADAMTS-13) in a patient with thrombotic thrombocytopenic purpura

AbstractAcquired thrombotic thrombocytopenic purpura (TTP) has been linked to severe deficiency of ADAMTS-13 activity caused by autoantibodies inhibitory to ADAMTS-13. We report data on a patient with confirmed TTP who had severely reduced ADAMTS-13 activity but showed no ADAMTS-13 inhibition in a widely used fluid phase activity assay. With a newly developed enzyme-linked immunosorbent assay, using immobilized recombinant ADAMTS-13, we found high titers of IgM and IgG antibodies that bound to ADAMTS-13, but did not neutralize protease activity. These autoantibodies probably influenced the half-life of ADAMTS-13 or its binding to the endothelial cell surface, thereby compromising ADAMTS-13 activity in vivo. Given that ADAMTS-13 may interact physiologically with various receptors or ligands, the occurrence, distribution, and the epitope mapping of nonneutralizing antibodies will be an important area for future research.

Is ADAMTS-13 deficiency specific for thrombotic thrombocytopenic purpura? No

Is ADAMTS-13 deficiency specific for thrombotic thrombocytopenic purpura? No

Platelets: Thrombotic Thrombocytopenic Purpura

Abnormalities of plasma von Willebrand factor (VWF) have been recognized to be associated with thrombotic thrombocytopenic purpura (TTP) for over 20 years. Patients with chronic, relapsing TTP have VWF multimers that are larger than normal, similar in size to those secreted by cultured endothelial cells. Recent observations have documented that a deficiency of a VWF-cleaving protease (termed ADAMTS13) may be responsible for the presence of these unusually large VWF multimers. Multiple mutations of the ADAMTS13 gene can result in ADAMTS13 deficiency and cause congenital TTP; autoantibodies neutralizing ADAMTS13 protease activity have been associated with acquired TTP. In Section I, Dr. Evan Sadler reviews the structure, biosynthesis, and function of the ADAMTS13 protease. He describes the mutations that have been identified in congenital TTP and describes the relationship of ADAMTS13 deficiency to the development of both congenital and acquired TTP. Dr. Sadler postulates that the development of TTP may be favored by conditions that combine increased VWF secretion, such as during the later stages of pregnancy, and decreased ADAMTS13 activity. In Section II, Dr. Bernhard Lämmle describes the assay methods for determining ADAMTS13 activity. Understanding the complexity of these methods is essential for understanding the difficulty of assay performance and the interpretation of assay data. Dr. Lämmle describes his extensive experience measuring ADAMTS13 activity in patients with TTP as well as patients with acute thrombocytopenia and severe illnesses not diagnosed as TTP. His data suggest that a severe deficiency of ADAMTS13 activity (< 5%) is a specific feature of TTP. However, he emphasizes that, although severe ADAMTS13 deficiency may be specific for TTP, it may not be sensitive enough to identify all patients who may be appropriately diagnosed as TTP and who may respond to plasma exchange treatment. In Section III, Dr. James George describes the evaluation and management of patients with clinically suspected TTP, as well as adults who may be described as having hemolytic-uremic syndrome (HUS). Dr. George presents a classification of TTP and HUS in children and adults. Appropriate evaluation and management are related to the clinical setting in which the diagnosis is considered. A clinical approach is described for patients in whom the diagnosis of TTP or HUS is considered (1) following bone marrow transplantation, (2) during pregnancy or the postpartum period, (3) in association with drugs which may cause TTP either by an acute immune-mediated toxicity or a dose-related toxicity, (4) following a prodrome of bloody diarrhea, (5) in patients with autoimmune disorders, and (6) in patients with no apparent associated condition who may be considered to have idiopathic TTP. Patients with idiopathic TTP appear to have the greatest frequency of ADAMTS13 deficiency and appear to be at greatest risk for a prolonged clinical course and subsequent relapse. Management with plasma exchange has a high risk of complications. Indications for additional immunosuppressive therapy are described.