Moderate Deficiency of ADAMTS13 in Thrombotic Microangiopathy Is Associated with Poor Survival Regardless of Plasma Exchange

Abstract Introduction: The ADAMTS13 assay is routinely ordered as part of the work-up for thrombotic microangiopathies (TMAs). While severe deficiency of ADAMTS13 activity (≤10%) is specific for the diagnosis of idiopathic TTP and identifies a group of patients who respond well to treatment with therapeutic plasma exchange (TPE), the implications of mild-to-moderate deficiency (11-66%) remain unclear. This study aims to elucidate the presenting characteristics, clinical outcomes and diagnoses, and responses to TPE in TMA patients with non-critically low ADAMTS13 activity. Methods: Two hundred-fifty two adult TMA patients from 3 large academic medical centers over a 10-year period were identified based on the presence of microangiopathic hemolytic anemia (schistocytes on smear, platelets <150,000/μL) and available ADAMTS13 results. Sixty-eight patients with ADAMTS13 ≤10% were excluded from the current analysis. Three cohorts were identified from the remaining 184 patients based on their ADAMTS13 activity level: 45 moderately deficient (11-40%), 84 mildly deficient (41-66%), and 55 non-deficient (≥67%). The ANOVA and chi-square tests were used for intergroup comparisons. Kaplan-Meier curves with log-rank analysis were used to assess survival differences where day 0 was defined as the day ADAMTS13 assay was sent. Results: With the exception of younger age in the non-deficient group, the 3 cohorts were similar with respect to gender and ethnicity, presenting signs and symptoms, clinical history and laboratory values (Table 1). Whereas the frequency of secondary TMA attributable to drugs, malignancy, hypertension, hemolytic-uremic syndrome (HUS), and autoimmune disease was not different across these three cohorts, patients with moderate reduction in ADAMTS13 activity were more likely to have disseminated intravascular coagulation (DIC) and sepsis compared to the mildly- and non-deficient cohorts (p=0.001). Additionally, the moderately deficient cohort had slower recovery of platelet count by day 4 (p=0.043) and significantly lower 90-day survival (Figure 1, p=0.01 by log-rank). The role of TPE in patients with moderate ADAMTS13 deficiency was evaluated. TPE was performed in 10 of 45 patients (22%). Presenting features among these 10 patients were not significantly different from the 33 patients (73%) who did not receive TPE (2 patients receiving <3 treatments were excluded). The 90-day survival between these two subgroups was not significantly different (Figure 2, p=0.48 by log-rank). Conclusions: Moderate ADAMTS13 deficiency (11-40%) in patients with TMA is more frequently associated with an underlying diagnosis of DIC and sepsis and portends slower recovery as well as worse survival. A modest reduction of ADAMTS13 activity may be a result of disease manifestation rather than the cause. Therefore, therapy directed at the underlying disease processes may lead to better outcomes than routine plasma exchange for these patients. Figure 2 Figure 2. Figure 3 Figure 3. Disclosures No relevant conflicts of interest to declare.

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Thienopyridine-Associated Thrombotic Thrombocytopenia Purpura: Updated Antibody Results From the SERF-TTP Study.

Blood ◽

10.1182/blood.v114.22.892.892 ◽

2009 ◽

Vol 114 (22) ◽

pp. 892-892

Author(s):

Anaadriana Zakarija ◽

Thanh Ha Luu ◽

Hau C. Kwaan ◽

June McKoy ◽

Ivy Weiss ◽

...

Keyword(s):

Plasma Exchange ◽

Neutralizing Antibodies ◽

Conflicts Of Interest ◽

Therapeutic Plasma Exchange ◽

Severe Thrombocytopenia ◽

Adamts13 Activity ◽

Laboratory Findings ◽

History Of ◽

Adamts13 Deficiency ◽

Drug Dependent

Abstract Abstract 892 Background: The thienopyridines, ticlopidine and clopidogrel, have been associated with thrombotic thrombocytopenia purpura (TTP). However, few studies have reported information on antibodies to ADAMTS13 among patients with thienopyridine-associated TTP. We previously reported on two mechanistic pathways of thienopyridine-associated TTP with some overlapping features. Evaluation of ADAMTS13 autoantibodies was undertaken to improve understanding of these syndromes. Methods: Clinical and laboratory findings were evaluated for 30 ticlopidine-, 10 clopidogrel-associated TTP cases, and 54 cases of idiopathic TTP. Results: Among patients with thienopyridine-induced TTP, those with a history of ticlopidine versus clopidogrel use were more likely to present with severe thrombocytopenia (platelet < 20,000) (90% versus 13%), severe ADAMTS13-deficiency (80% versus 0%), and neutralizing antibodies to ADAMTS13 (100% versus 0%), and were less likely to have less than a two week history of thienopyridine exposure (0% versus 50%) (p<0.05 for each comparison). They were also more likely to survive following therapeutic plasma exchange (TPE) (85% versus 50%). 2 patients exposed to clopidogrel later relapsed and had similar characteristics to idiopathic TTP patients with non-deficient ADAMTS13 activity. Conclusion: Ticlopidine causes TTP by a pathway involving a neutralizing autoantibody to ADAMTS13 while clopidogrel causes TTP by an ADAMTS13-independent pathway. Although ADAMTS13 autoantibodies are present in both idiopathic and ticlopidine-associated TTP, spontaneous relapses are not seen in ticlopidine-associaated TTP, suggesting that drug-dependent antibodies are present. Clopidogrel associated TTP is distinct from idiopathic TTP in that ADAMTS13 autoantibodies are absent and response to TPE is poor. Disclosures: No relevant conflicts of interest to declare.

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Survival and relapse in patients with thrombotic thrombocytopenic purpura

Blood ◽

10.1182/blood-2009-09-243790 ◽

2010 ◽

Vol 115 (8) ◽

pp. 1500-1511 ◽

Cited By ~ 307

Author(s):

Johanna A. Kremer Hovinga ◽

Sara K. Vesely ◽

Deirdra R. Terrell ◽

Bernhard Lämmle ◽

James N. George

Keyword(s):

Plasma Exchange ◽

Thrombotic Thrombocytopenic Purpura ◽

Signs And Symptoms ◽

Population Based ◽

Adamts13 Activity ◽

Thrombocytopenic Purpura ◽

Adamts13 Deficiency ◽

Estimated Risk ◽

Subsequent Relapse ◽

Organ Dysfunctions

AbstractSurvival of patients with thrombotic thrombocytopenic purpura (TTP) improved dramatically with plasma exchange treatment, revealing risk for relapse. The Oklahoma TTP Registry is a population-based inception cohort of all 376 consecutive patients with an initial episode of clinically diagnosed TTP (defined as microangiopathic hemolytic anemia and thrombocytopenia with or without signs and symptoms of ischemic organ dysfunctions) for whom plasma exchange was requested, 1989 to 2008. Survival was not different between the first and second 10-year periods for all patients (68% and 69%, P = .83) and for patients with idiopathic TTP (83% and 77%, P = .33). ADAMTS13 activity was measured in 261 (93%) of 282 patients since 1995. Survival was not different between patients with ADAMTS13 activity < 10% (47 of 60, 78%) and patients with 10% or more (136 of 201, 68%, P = .11). Among patients with ADAMTS13 activity < 10%, an inhibitor titer of 2 or more Bethesda units/mL was associated with lower survival (P = .05). Relapse rate was greater among survivors with ADAMTS13 activity < 10% (16 of 47, 34%; estimated risk for relapse at 7.5 years, 41%) than among survivors with ADAMTS13 activity of 10% or more (5 of 136, 4%; P < .001). In 41 (93%) of 44 survivors, ADAMTS13 deficiency during remission was not clearly related to subsequent relapse.

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The Frequency of Rheumatic Disease Autoantibodies in Patients with ADAMTS13-Deficient Thrombotic Thrombocytopenia Purpura (TTP).

Blood ◽

10.1182/blood.v110.11.2090.2090 ◽

2007 ◽

Vol 110 (11) ◽

pp. 2090-2090

Author(s):

Karen K. Swisher ◽

Qurana F. Lewis ◽

Judith A. James ◽

Johanna A. Kremer Hovinga ◽

Bernhard Lämmle ◽

...

Keyword(s):

Rheumatic Disease ◽

Plasma Exchange ◽

Potential Risk ◽

Lupus Erythematosus ◽

Autoimmune Disorders ◽

First Episode ◽

Adamts13 Activity ◽

Disease Systemic Lupus Erythematosus ◽

Increased Risk ◽

Adamts13 Deficiency

Abstract Patients who have TTP associated with acquired, severe ADAMTS13 deficiency have an autoimmune etiology and therefore may have increased risk for additional autoimmune disorders. The Oklahoma TTP-HUS Registry enrolled 247 consecutive patients with their first episode of clinically diagnosed TTP from 11-13-1995 (the date of our initial ADAMTS13 measurement) to 6-30-2006 for whom plasma exchange treatment was requested; ADAMTS13 activity was measured in 228 (92%) of patients immediately before their first plasma exchange treatment; 42 (18%) patients had ADAMTS13 activity <10%. Three patients were excluded from this analysis because of preexisting systemic rheumatic disease (systemic lupus erythematosus (SLE), 2, Sjogren’s syndrome, 1). To examine the potential risk for development of autoimmune disorders, we measured screening autoantibodies (ANA, dsDNA, Sm, nRNP, Ro, La, ribosomal P, Jo-1, anti-phospholipid (aPL) IgG and IgM) in 34 of the 39 (87%) remaining patients. The median age at initial presentation was 39 years (range 9–71 years); 27 (79%) patients were women; 13 (41%) patients were black. Autoantibodies were measured by indirect immunofluorescence, immunodiffusion, or ELISA. Measurements were performed only once in 16 patients; in 18 patients 2–3 measures were performed over a period of 13 to 126 months. Rheumatic disease autoantibodies TTP patients *1 patient had a maximum titer of >1:3240 in 2 samples; 1 patient developed overt SLE and his titer decreased with treatment. ANA ≥1:40 on at least one occasion 33/34 (97%) ANA ≥1:120 on at least one occasion 29/34 (85%) ANA measured ≥2 times, increasing titer 14/16* (88%) Anti-dsDNA ≥1:30 12/34 (35%) Anti-Ro positive 14/29 (48%) Anti-Sm positive 1/34 (3%) Anti-nRNP positive 1/34 (3%) aPL IgG and/or IgM ≥moderate positive 4/34 (12%) No patients had positive tests for anti-La, anti-Ribo-P, or anti-Jo-1. 23 (68%) of the 34 patients had a positive test for one or more rheumatic disease autoantibodies (dsDNA, nRNP, Ro, La, or moderately positive aPLs). 4 of the 34 patients died during their initial episode; the remaining 30 patients have been followed for a median of 6.4 years (range, 1–11.5 years). During this time only 1 patient has developed clinically evident SLE; no other patients have developed systemic rheumatic diseases. Conclusions: A high prevalence of rheumatic disease-associated autoantibodies were found in a cohort of consecutive patients with TTP associated with acquired severe ADAMTS13 deficiency. The presence of dsDNA and Ro autoantibodies and increasing ANA titers suggest that patients with ADAMTS13-deficientTTP may have a potential risk for developing additional autoimmune disorders such as SLE or Sjogren’s syndromes. [3] These serologic observations support clinical observations that presenting features of TTP and SLE may overlap.

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Are Patients Who Have Recovered From ADAMTS13-Deficient Thrombotic Thrombocytopenia Purpura (TTP) at Risk for Developing Systemic Lupus Erythematosus (SLE)?

Blood ◽

10.1182/blood.v116.21.2519.2519 ◽

2010 ◽

Vol 116 (21) ◽

pp. 2519-2519

Author(s):

Deirdra R. Terrell ◽

Zayd Al-Nouri ◽

Judith A. James ◽

Johanna A. Kremer Hovinga Strebel ◽

Bernhard Lämmle ◽

...

Keyword(s):

At Risk ◽

Clinical Features ◽

Lupus Erythematosus ◽

Conflicts Of Interest ◽

Population Data ◽

First Episode ◽

Adamts13 Activity ◽

Acr Criteria ◽

Adamts13 Deficiency

Abstract Abstract 2519 TTP associated with acquired, ADAMTS13-deficiency and SLE are both autoimmune disorders that occur preferentially in young, black women and they have many similar clinical features. TTP may occur in patients previously diagnosed with SLE, or patients may develop SLE following recovery from TTP. In addition, TTP may be quite difficult to distinguish from SLE patients with severe hematologic manifestations. We compared the prevalence of SLE-associated autoantibodies in TTP patients to published population data using 95% confidence intervals (CI). The Oklahoma TTP Registry enrolled 292 consecutive patients with their first episode of clinically diagnosed TTP from 11–13-1995 (date of our initial ADAMTS13 measurement) to 7–31-2009; ADAMTS13 activity was measured in 271 (93%) patients; 64 (24%) patients had ADAMTS13 activity <10%, 63 were evaluated for SLE-associated autoantibodies, including 2 patients with a previous diagnosis of SLE. Serum from the patient's acute initial episode was used for analysis. The prevalence of ANA, anti-dsDNA, anti-Ro, and aPL in TTP patients was significantly higher than published population data; prevalences of anti-nRNP, anti-Sm, and anti-La were not different. Autoantibody TTP (95% CI) Population % ANA ≥1:40 89% (78%–95%) 0–27% ≥1:120 56% (42%–68%) 0% Anti-dsDNA ≥1:30 43% (30%–56%) 3% Anti-Ro OD>0.350 17% (8%–29%) 3% aPL IgM ≥20 PL units 15% (7%–26%) 2% Because of the increased prevalence of SLE-associated autoantibodies, we evaluated our TTP patients for the America College of Rheumatology (ACR) criteria for SLE (presence of ≥4 of 11 criteria suggests the diagnosis of lupus); abnormalities associated with any TTP episode were not counted in this evaluation of clinical criteria for SLE. By definition ACR criteria can be fulfilled serially or simultaneously over a lifetime. Evaluations were completed between 6-1-2007 and 5-1-2009 on 38/42 (90%) eligible patients (alive, non-institutionalized, no previous SLE diagnosis) consisting of physical examination, review of available lifetime medical records, and serial laboratory evaluations. Patients have been followed for a median of 8.3 years (range, 1–14 years). During this time, 3 (8%) developed clinically evident SLE requiring treatment 1, 5, and 70 months after their initial TTP episodes. Among the other 35 patients, 3 (8%) have ≥4 SLE classification criteria by medical record review (1 had pre-existing Sjögren's syndrome and receives treatment; 2 have minimal clinical features and are not actively treated for SLE); 9 (24%) have 3 criteria; 16 (42%) have 2 criteria; 6 (16%) have 1 criterion; and 1 (2%) patient has no ACR criteria for SLE. All patients continue to be followed and clinically evaluated for potential intervention. SLE diagnosis is a clinical designation and because of the lack of disease modifying drugs, routine follow-up is standard of care unless the patient is symptomatic. Conclusions: [1] A high prevalence of SLE-associated autoantibodies was present in a cohort of consecutive patients with TTP associated with acquired severe ADAMTS13 deficiency. [2] The presence of anti-dsDNA, anti-Ro, aPL and high titers of ANA suggest that patients with ADAMTS13-deficient TTP may be at risk for developing SLE. [3] During long-term follow-up, 6 (16%) of 38 patients have developed overt SLE or ACR criteria without an established diagnosis of SLE. Careful continuing evaluation following recovery from TTP is important. Disclosures: No relevant conflicts of interest to declare.

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Correlation Of ADAMTS13 Activity With Baseline Characteristics and Management Patterns In Patients With Suspected Thrombotic Thrombocytopenic Purpura In The State Of Rhode Island

Blood ◽

10.1182/blood.v122.21.3556.3556 ◽

2013 ◽

Vol 122 (21) ◽

pp. 3556-3556

Author(s):

Nathan T. Connell ◽

Joseph D. Sweeney

Keyword(s):

Plasma Exchange ◽

Thrombotic Thrombocytopenic Purpura ◽

Rhode Island ◽

Turnaround Time ◽

Activity Level ◽

Activity Levels ◽

Adamts13 Activity ◽

Thrombocytopenic Purpura ◽

Baseline Characteristics ◽

Pre Treatment

Abstract Introduction While the activity level of ADAMTS13 can be helpful in diagnosing patients with thrombotic thrombocytopenic purpura (TTP), the current long turnaround time of this test for most institutions limits its role in early clinical decision-making about the initiation of plasma exchange. Levels of ADAMTS13<10% are pathognomonic of TTP and levels in excess of 10% indicate an alternate cause of thrombotic microangiopathy. The aim of the study was to look at recent practice in the State of Rhode Island regarding the criteria for initiation of plasma exchange with a subsequent categorization of those patients based on ADAMTS13 activity levels. Methods Patients with a diagnosis of TTP were identified from hospital records of the major hospitals in Rhode Island which perform therapeutic apheresis in calendar years 2011 and 2012. From a chart review and blood bank records, baseline clinical parameters were collected, the number of therapeutic plasma exchanges (TPE) performed and the volume of plasma utilized. Pre-treatment ADAMTS13 activity was recorded if available in addition to the number of days from the initiation of TPE to test result availability. An analysis was performed to examine if patients who had a pre-treatment ADAMTS13 activity level ≤10% differed in baseline characteristics or response to TPE from those with activity levels >10%. Based on the normality of the distribution of the data, independent t-tests or Wilcoxon rank-sum tests were performed using SAS version 9.3. Results During this two year period, 24 patients received plasma exchange in Rhode Island for a presumptive diagnosis of TTP. The mean age was 47 years (range 20-89 years) and 38% were male. ADAMTS13 activity was available for 20 patients and 7 (30% of those exchanged) had documented pre-treatment activity levels ≤10% consistent with TTP. The median turnaround time for the ADAMTS13 assay was 10 days (range 2-52). Mean baseline parameters at the time of presentation are shown in the table. As expected, creatinine levels were lower in those patients with true TTP (p=0.0410). ADAMTS13 activity level was predictive of the number of days to a platelet count ≥150 x 109/L (Pearson correlation 0.56; p-value 0.0458). Overall, 4238 units of plasma were utilized for exchange. Of these 4238 units, 1886 were transfused to patients who were subsequently shown to have an ADAMTS13 activity >10%, and 813 of the 1886 units (20% of all plasma exchanged) were transfused after the results of enzyme activity were available in this population. Conclusions Based on an ADAMTS13 >10%, a significant volume of plasma was unnecessarily transfused. Reducing the turnaround time for the ADAMTS13 assay in tertiary care centers could help clinicians better determine which patients will benefit from plasma exchange, avoiding the morbidity and expense associated with large volume plasma exchange. Disclosures: No relevant conflicts of interest to declare.

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Adamts-13 Inhibitor Testing Is Often Negative on Initial Testing

Blood ◽

10.1182/blood-2018-99-119399 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 5051-5051

Author(s):

Hina Chaudhry ◽

Michelle Sholzberg ◽

Katerina Pavenski

Keyword(s):

Conflicts Of Interest ◽

Thrombus Formation ◽

Genetic Defect ◽

Reference Laboratory ◽

Adamts13 Activity ◽

Repeated Testing ◽

Inhibitor Titre ◽

Adamts13 Deficiency ◽

Platelet Thrombus ◽

Von Willebrand

Abstract Background: Thrombotic thrombocytopenic purpura (TTP) presents with microangiopathic hemolytic anemia and thrombocytopenia and is caused by severe ADAMTS13 deficiency. TTP can be the result of autoantibodies to ADAMTS13 or genetic defect in the ADAMTS13 gene. ADAMTS-13 is an enzyme that specifically cleaves unusually large von Willebrand Factor (VWF) multimers which mediate platelet thrombus formation under high shear. When ADAMTS13 is deficient, unusually large VWF multimers accumulate causing excessive platelet aggregation and thrombosis in the microvasculature. Methods: St. Michael's Hospital, Toronto is home to a large reference laboratory for special coagulation. We use a commercial ELISA Technoclone Technozym ADAMTS-13 activity assay for the determination of ADAMTS-13 activity and Technoclone Technozym ADAMTS-13 inhibitor assay to identify anti-ADAMTS-13 antibodies. We send samples to another Canadian laboratory for validation of our results as they use an in-house ELISA assay for ADAMTS13 activity and anti-ADAMTS13 antibody. Results: We performed a retrospective review of all ADAMTS13 activity tests performed by our laboratory between January 1, 2013 and June 30, 2018. The total number of tests was 466 from 203 unique patients. 24% had an ADAMTS-13 activity under 10% (N = 144) which is consistent with the diagnosis of TTP. When specimens with severe ADAMTS-13 deficiency were tested for presence of anti-ADAMTS13 antibody, 46% were negative. Four of these specimens were sent to the other laboratory and all had detectable, albeit very low titre, inhibitors. Furthermore, on repeated testing over the study period, the vast majority of patients who presented with low ADAMTS13 activity and no detectable antibody subsequently became antibody positive. Fifty-two patients remained antibody negative by our internal and send-out testing. Five of them were known to have or were subsequently diagnosed with hereditary TTP (hTTP). Only one patient continues to have negative antibody but whose clinical course is not consistent with hTTP. Conclusions: We found that a commercial ADAMTS13 (Technoclone Technozym) antibody assay is falsely negative in a substantial proportion of patients with autoimmune TTP, the majority of which likely had a low titer inhibitor, below the threshold of test detection. More sensitive assays and/or repeated testing, presumably as inhibitor titre increases during the course of the disease, may detect antibody presence in the majority of samples of patients with autoimmune TTP. This is an important finding as this could impact the types of therapies offered to patients with negative antibody screens and may also avoid unnecessary, expensive genetic testing . Disclosures No relevant conflicts of interest to declare.

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Correction of ADAMTS13 Deficiency by AAV-Mediated Gene Transfer of a C-Terminal Truncated ADAMTS13 Variant In a Murine Model

Blood ◽

10.1182/blood.v116.21.251.251 ◽

2010 ◽

Vol 116 (21) ◽

pp. 251-251

Author(s):

Sheng-Yu Jin ◽

Juan (Jenny) Xiao ◽

J. Fraser Wright ◽

X. Long Zheng

Keyword(s):

Gene Transfer ◽

Murine Model ◽

Bacterial Infections ◽

Rational Design ◽

Conflicts Of Interest ◽

Pediatric Population ◽

Pcr Analysis ◽

Adamts13 Activity ◽

Wild Type ◽

Adamts13 Deficiency

Abstract Abstract 251 ADAMTS13 is primarily synthesized in hepatic stellate cells. Plasma ADAMTS13 concentration in humans ranges from 0.5 to 1.2 μ g/ml. ADAMTS13 cleaves von Willebrand factor (VWF) after the Tyr1605 at the central A2 domain. This proteolytic cleavage is essential for removing newly released ultra large (UL) VWF from endothelial cell surface and further reducing the size of the released UL-VWF multimers in circulation under high flow shear stress. Deficiency of plasma ADAMTS13 activity results in thrombotic thrombocytopenic purpura (TTP), a life-threatening syndrome. Approximately 5–10% of all TTP cases are caused by a genetic deficiency of ADAMTS13 and known as hereditary TTP (or Upshaw-Schulman syndrome). Patients with this syndrome may present as neonates or during early childhood with unexplained jaundice, thrombocytopenia, and microangiopathic hemolytic anemia. If left untreated, central nervous system abnormality, chronic renal insufficiency and end-stage renal failure may develop in some cases. To date, the only treatment for hereditary TTP is intermittent infusion of fresh frozen plasma. The complications associated with administration of plasma including adverse events with central line placement, bacterial infections, chronic hepatitis C and allergic reactions to plasma proteins remain problematic, particularly in pediatric population. To develop a better therapy, we explored expression of an ADAMTS13 variant with adeno associated virus (AAV) serotype 2-mediated gene transfer in Adamts13-/- mice. We showed that a single injection of AAV2 encoding an ADAMTS13 variant truncated after the spacer domain (i.e. construct S), either under a ubiquitous promoter, elongation factor 1a (EF1a), or under a liver-specific promoter, human alpha 1-anti-trypsin (hAAT), at the vector doses between 1.3×1012 and 1×1013 vg/kg, resulted in a sustained expression of recombinant S for approximately 19 weeks analyzed. The maximal levels of plasma ADAMTS13 activity were between 1.0 and 1.6 units/ml at 4–6 weeks of post vector administration. The ADAMTS13 activity was determined in murine plasma by cleavage of a murine-specific recombinant fluorescein-labeled VWF73 peptide (rF-mVWF73). The pooled murine plasma from wild-type (C57BL/6) mice was used for calibration, defined as having 1.0 unit/ml. Plasma VWF multimers were assessed at 2, 4, 8, 12, 16 and 19 weeks after the vector administration by 1% agarose gel electrophoresis and Western blotting. Our results showed that UL-VWF multimers were present in plasma of Adamts13-/- mice, but not in wild-type mice. The plasma UL-VWF multimers were, however, dramatically reduced or eliminated in Adamts13-/-mice expressing recombinant S. The size of VWF multimers appeared to be correlated with plasma ADAMTS13 activity. As expected, a real-time PCR analysis demonstrated that the transgene S mRNA was detected in the liver, lung, kidney, spleen, brain and heart after the injection of AAV2-EF1a-S, but restricted to the liver and heart after the injection of AAV2- hAAT-S. To assess the minimal AAV vector dose required to produce therapeutic levels of ADAMTS13 activity, we injected AAV2-EF1a-S and AAV2-hAAT-S at lower doses, i.e. 4×1011 and 1.3×1011vg/kg. The maximal levels of ADAMTS13 activity at the vector dose of 1.3×1011 vg/kg were detected 4–6 weeks after vector injection, which were 0.2 units/ml and 0.3 units/ml for AAV2-EF1a-S and AAV2-hAAT-S, respectively. However, the maximal levels of ADAMTS13 activity in Adamts13-/- mice receiving AAV2-EF1a-S and AAV2-hAAT-S at the vector dose of 4×1011 vg/kg reached 1.0 unit/ml and 1.4 unit/ml, respectively. These levels of plasma ADAMTS13 activity were comparable with those observed in wild type mice and in Adamts13-/- mice receiving higher doses of vector. Our results suggest that a vector dose of 4×1011 vg/kg appears to be sufficient to transduce the therapeutic levels of ADAMTS13 expression. In summary, we have demonstrated a successful correction of ADAMTS13 deficiency in a murine model using recombinant AAV2 encoding a C-terminal truncated ADAMTS13 variant S. Our ongoing study is to determine whether the expressed ADAMTS13 variant is efficacious to prevent Shiga toxin-induced TTP in Adamts13-/- and disease-susceptible strain (CAST/Ei). The results of our study may provide a molecular basis for a rational design of a gene therapy approach for hereditary TTP. Disclosures: No relevant conflicts of interest to declare.

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Assessment of the Plasmic Score Utility for Classification of Pediatric Thrombotic Microangiopathies

Blood ◽

10.1182/blood-2019-130608 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 1075-1075

Author(s):

Grace E Linder ◽

Steven Richard Sloan ◽

Pavan Bendapudi ◽

Robert Makar

Keyword(s):

Platelet Count ◽

Pediatric Patients ◽

Conflicts Of Interest ◽

Study Cohort ◽

Prediction Tool ◽

Adamts13 Activity ◽

Clinical Prediction ◽

Thrombotic Microangiopathies ◽

Adamts13 Deficiency ◽

Clinical Prediction Tool

Introduction: Thrombotic thrombocytopenic purpura (TTP) is a rare form of microangiopathic hemolytic anemia characterized by congenital or acquired deficiency of the enzyme ADAMTS13. Both inherited TTP (Upshaw-Schulman Syndrome) and acquired TTP can present in childhood. As TTP is particularly uncommon in pediatric patients, there are frequent delays in diagnosis that can prolong time to life-saving treatment with therapeutic plasma exchange (TPE). The PLASMIC score is a validated clinical prediction tool used to stratify adult patients with thrombotic microangiopathies (TMAs) based upon their risk of having severe ADAMTS13 deficiency. The purpose of this study is to characterize a cohort of pediatric patients presenting with TMAs and to determine whether the PLASMIC score can accurately identify those children at risk for severe ADAMTS13 deficiency. Methods: We created a registry of all consecutive pediatric cases of suspected TTP at 3 academic medical centers in Boston, MA from January 2004 through November 2018. Suspected cases were defined as any patient with TMA who received ADAMTS13 activity testing during this period. Patients were included in the cohort if they were ≤18 years-old, thrombocytopenic (platelet count less than lower limit of normal for age), and had schistocytes on peripheral blood smear. Exclusion criteria included individuals tested as outpatients and potential interferents with ADAMTS13 testing (hemolyzed specimen, total bilirubin >15 mg/dL, sample sent less than 24 hours after exposure to plasma). For each patient, the ADAMTS13 test result as well as additional laboratory, demographic, and clinical parameters were recorded. The PLASMIC score was calculated for each patient. Results: Of the 125 unique pediatric patients who underwent ADAMTS13 testing during the study period, 59 presented with a thrombotic microangiopathy and met the inclusion criteria. Nine of the 59 patients (15.3%) had severe ADAMTS13 deficiency with ADAMTS13 activity of ≤10%. Eight of these 9 patients had detectable autoantibody inhibitor titers, consistent with acquired/immune TTP. One patient with severe ADAMTS13 deficiency had a history of renal transplant and was the only patient with ADAMTS13 levels ≤10% who had no detectable inhibitor. Compared to patients with ADAMTS13 levels >10%, patients with severe ADAMTS13 deficiency were older, predominantly female, and more frequently presented with neurological symptoms (see table). At the time of ADAMTS13 testing, patients with severe ADAMTS13 deficiency also had a lower platelet count, a higher LDH, a higher reticulocyte count, and higher levels of total and indirect bilirubin. There were non-significant trends toward improved one-year and overall survival in patients with ADAMTS13 levels ≤10%. Forty-eight patients in the cohort had all necessary data for calculation of the PLASMIC score. As the youngest patient with severe ADAMTS13 deficiency in this cohort was 3 years-old, we restricted our analysis to patients 2 years and older (N=41). All pediatric patients with ADAMTS13% ≤10% in our cohort had a PLASMIC score of 6 or 7. Nine out of 16 patients with a PLASMIC score of >5 had severe ADAMTS13 deficiency. The C statistic for the resultant ROC curve was 0.92 (95% CI 0.796 to 0.983). Conclusion: The small number of pediatric patients with TTP identified over the 14-year period of our study cohort emphasizes the rarity of this disease in children and the potential utility for a clinical prediction tool to aid in diagnosis and to help determine on whom ADAMTS13 testing should be performed. The PLASMIC score can accurately identify pediatric patients at high risk for severe ADAMTS13 deficiency, facilitating rapid diagnosis and initiation of appropriate therapy. Figure Disclosures No relevant conflicts of interest to declare.

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Therapeutic Plasma Exchange for the Treatment of Thrombotic Microangiopathy without Severe ADAMTS13 Deficiency: A Propensity Score-Matched Study

Blood ◽

10.1182/blood.v126.23.3471.3471 ◽

2015 ◽

Vol 126 (23) ◽

pp. 3471-3471 ◽

Cited By ~ 1

Author(s):

Ang Li ◽

Robert S Makar ◽

Shelley Hurwitz ◽

Lynne Uhl ◽

Richard M. Kaufman ◽

...

Keyword(s):

Platelet Count ◽

Propensity Score ◽

Hospital Mortality ◽

Primary Outcome ◽

Activity Level ◽

Adamts13 Activity ◽

Adamts13 Deficiency ◽

Baseline Characteristics ◽

Secondary Outcomes ◽

Count Recovery

Abstract Introduction: Thrombotic microangiopathies (TMA) are a group of uncommon disorders characterized clinically by the presence of thrombocytopenia and microangiopathic hemolytic anemia (MAHA). Therapeutic plasma exchange (TPE) is a proven treatment for cases of autoimmune thrombotic thrombocytopenic purpura (TTP) characterized by an ADAMTS13 activity level of ≤10%, but the efficacy of TPE in TMA with an ADAMTS13 activity level of >10% remains controversial. Methods: We conducted a retrospective cohort study of 186 adult patients included in the Harvard TMA Research Collaborative registry who presented with MAHA and thrombocytopenia concerning for TTP but an ADAMTS13 activity level of >10%. A propensity score (PS) logistic regression model was constructed based on 11 clinically relevant confounding variables: age; sex; ethnicity; Charlson Comorbidity Index (CCI); history of prior solid organ or bone marrow transplant; the presence of neurologic symptoms; the presence of sepsis, shock, or multiorgan failure (MOF); platelet count; creatinine; LDH; and INR. Matching was performed using a 1:1 nearest neighbor method without replacement within a set caliper distance. Standardized differences were used to assess the quality of matching and ensure balance of baseline characteristics. The primary outcome was 90-day survival. Secondary outcomes included in-hospital mortality, percent of patients experiencing platelet count recovery, time to platelet count recovery, and hospital length of stay (LOS). Results: Prior to matching, patients treated with TPE (N=71) had a lower acuity of illness compared to untreated patients (N=115) as reflected by a lower mean CCI (2.3 vs. 3.4, P = 0.003), lower mean INR (1.1 vs. 1.3, P = 0.02), and lower incidence of sepsis, shock or MOF (23% vs. 36%, P = 0.06). Consistent with this confounding, TPE in the pre-matched cohort appeared to be associated with reduced mortality at 90 days (HR 0.51, P = 0.01). The PS match was performed to address these imbalances and resulted in 59 TPE-treated patients paired to 59 untreated controls. After matching, baseline characteristics of the treated and untreated groups were well balanced, with a standardized difference of ≤11% in all PS variables (see Figure). In contrast to the unmatched cohort, Cox regression analysis stratified by matched pairs showed no significant difference in the primary outcome of 90-day survival between the treated and untreated groups (HR 0.88, 95% CI 0.44-1.8, P = 0.72) (see Table). We performed subgroup analyses by age, diagnostic category, and ADAMTS13 activity level and again did not observe any benefit to TPE. With regard to secondary outcomes, in-hospital mortality (OR 0.77, P = 0.53), percent of patients with platelet count recovery (OR 1.6, P = 0.21), median time to platelet count recovery (6 vs. 6 days, P = 0.99), and median hospital LOS (14 vs. 18 days, P = 0.93) did not differ significantly between the two groups. Conclusions: In the absence of a randomized controlled trial, PS matching represents a rigorous statistical approach to study the effect of treatment while adjusting for differences in baseline characteristics across groups of patients. Here we have used PS matching to assess the efficacy of TPE in the management of TMA associated with an ADAMTS13 activity level of >10%. Our data indicate that there is no benefit from TPE for this diverse group of TMA patients without severe ADAMTS13 deficiency. Figure 1. Figure 1. Figure 2. Figure 2. Disclosures No relevant conflicts of interest to declare.

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Factor V Leiden Is Not a Risk Factor for Thrombotic Microangiopathies without Severe ADAMTS13 Deficiency.

Blood ◽

10.1182/blood.v104.11.850.850 ◽

2004 ◽

Vol 104 (11) ◽

pp. 850-850

Author(s):

Johanna A. Kremer Hovinga ◽

Soraya Krieg ◽

Jan-Dirk Studt ◽

Irmela Sulzer ◽

Bernhard Lammle

Keyword(s):

Risk Factor ◽

Clinical Diagnosis ◽

Factor V Leiden ◽

Base Line ◽

Factor V ◽

Adamts13 Activity ◽

Chi Square ◽

Available N ◽

Chi Square Test ◽

Adamts13 Deficiency

Abstract Background: Severe deficiency of ADAMTS13, the VWF-cleaving protease (<5% of normal) is a specific finding for a thrombotic microangiopathy (TMA) most often labeled clinically as thrombotic thrombocytopenic purpura (TTP). The sensitivity of severe ADAMTS13 deficiency for the clinical diagnosis of idiopathic TTP, however, remains equivocal with an overall sensitivity of about 60% (range 33–100%). This indicates, that other pathogenetic factors may lead to a condition clinically indistinguishable from that seen in severe ADAMTS13 deficiency. Recently, Raife (Blood2002;99:437–442) concluded from a small case series including 27 Caucasians with acute TMA, that factor V Leiden (FVL) represented such a risk factor in a subset of TMA patients without severe ADAMTS13 deficiency. The consequence could be a more individualized treatment regimen including anticoagulant drugs complementing plasma exchange therapy in this subset of patients. Therefore, our aim was to estimate the prevalence and risk of FVL carriers in relation to ADAMTS13 activity levels and clinical TMA diagnosis in a large patient group presenting with acute TMA. Methods: Between January 2001 and July 2003 ADAMTS13 activity was determined in 396 consecutive patients referred to our laboratory for diagnostic purposes. Based on the clinical and patient data provided by the referring clinicians 131 patients were excluded from this study (no clinical information available [n=45]; no acute TMA [50]; no plasma left [26]; non-Caucasians [3] and various reasons [7]). The remaining 265 patients were assigned to three principal clinical categories: idiopathic TMA (n=204, among them 80 patients with the clinical diagnosis of TTP and 124 cases with hemolytic-uremic syndrome [HUS]), secondary TMA (30) and TMA not further specified (31). ADAMTS13 activity was assessed by a quantitative immunoblotting assay. FVL carrier-ship was determined by a commercial aPTT-based APC resistance assay and in cases with prolonged base-line aPTT (>42s), decreased factor V clotting activity (<50%) or equivocal APC sensitivity ratio by genotyping using DNA purified from patient’s plasma. Results: A severe ADAMTS13 deficiency was found in 22% (59/265) of patients investigated, among them none of the HUS cases but 49 patients diagnosed as having TTP. Twenty-one (7.9%) of all patients were FVL carriers consistent with the FVL prevalence reported for Europe (0.9–14%), especially however, for Germany (4–8.9%) and Switzerland (3–7%), who referred most patients (176 [66.4%] and 52 [19.6%], respectively). Similar allele frequencies were observed among patients diagnosed as TTP (6.3%, 5/80) or HUS (8.9%, 11/124). The difference between the latter two was statistically not significant (p=0.497, chi-square test). FVL was found in 6.8% (4/59) of patients with severe ADAMTS13 deficiency and in 8.3% (17/206) without severe ADAMTS13 deficiency (p=0.712, chi-square test). Data did not change when the cut-off level for severe ADAMTS13 deficiency was raised to an ADAMTS13 activity of 10%. Conclusions: We conclude, that FVL is not more prevalent in patients with acute TMA without severe ADAMTS13 deficiency than in TMA patinets with severe ADAMTS13 deficiency. Furthermore, there is no difference in the FVL prevalence in patients diagnosed as having HUS or TTP. Based on our results, FVL is not a risk factor for acute TMA and pathogenetically not involved in acute TMA without ADAMTS13 deficiency.

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