ADAMTS13 Deficiency Research Articles

Acquired thrombotic thrombocytopenic purpura without detectable anti-ADAMTS13 antibodies: a possible underlying autoimmune mechanism.

In up to 25% of patients with acquired TTP, anti-ADAMTS13 antibodies are not identified, the mechanism resulting from ADAMTS13 deficiency remains unidentified (uTTP). In this study, we provide further insights on clinical presentation and outcome of uTTP. In patients with baseline undetectable anti-ADAMTS13 antibodies, usual features of iTTP (young age, cerebral involvement, severe thrombocytopenia) with no other associated context than a history of systemic autoimmune disease or pregnancy, should prompt to consider the diagnosis of iTTP.

The Highs and Lows of ADAMTS13 Activity.

Severe deficiency of ADAMTS13 (<10 iu/dL) is diagnostic of thrombotic thrombocytopenic purpura (TTP) and leads to accumulation of ultra-large vWF multimers, platelet aggregation, and widespread microthrombi, which can be life-threatening. However, the clinical implications of a low ADAMTS13 activity level are not only important in an acute episode of TTP. In this article, we discuss the effects of low ADAMTS13 activity in congenital and immune-mediated TTP patients not only at presentation but once in a clinical remission. Evidence is emerging of the clinical effects of low ADAMTS13 activity in other disease areas outside of TTP, and here, we explore the wider impact of low ADAMTS13 activity on the vascular endothelium and the potential for recombinant ADAMTS13 therapy in other thrombotic disease states.

The Phenomenon of Thrombotic Microangiopathy in Cancer Patients.

Thrombotic microangiopathy (TMA) encompasses a range of disorders characterized by blood clotting in small blood vessels, leading to organ damage. It can manifest as various syndromes, including thrombotic thrombocytopenic purpura (TTP), hemolytic-uremic syndrome (HUS), and others, each with distinct causes and pathophysiology. Thrombo-inflammation plays a significant role in TMA pathogenesis: inflammatory mediators induce endothelial injury and activation of platelet and coagulation cascade, contributing to microvascular thrombosis. Primary TMA, such as TTP, is primarily caused by deficient ADAMTS13 metalloproteinase activity, either due to antibody-mediated inhibition or intrinsic enzyme synthesis defects. In cancer patients, a significant reduction in ADAMTS13 levels and a corresponding increase in VWF levels is observed. Chemotherapy further decreased ADAMTS13 levels and increased VWF levels, leading to an elevated VWF/ADAMTS13 ratio and increased thrombotic risk. Drug-induced TMA (DITMA) can result from immune-mediated or non-immune-mediated mechanisms. Severe cases of COVID-19 may lead to a convergence of syndromes, including disseminated intravascular coagulation (DIC), systemic inflammatory response syndrome (SIRS), and TMA. Treatment of TMA involves identifying the underlying cause, implementing therapies to inhibit complement activation, and providing supportive care to manage complications. Plasmapheresis may be beneficial in conditions like TTP. Prompt diagnosis and treatment are crucial to prevent serious complications and improve outcomes.

Practical Considerations for the Use of the Rapid AcuStar® ADAMTS13 Activity Assay in the Diagnosis of Acute Thrombotic Thrombocytopenic Purpura (TTP).

Introduction: Conventional practice in the management of acute TTP entails empirical treatment of suspected cases whilst awaiting confirmatory ADAMTS13 deficiency testing. Rapid ADAMTS13 assays offer increased accessibility and rapid diagnostics. The new automated HemosIL AcuStar® ADAMTS13 assay has seen increasing use among UK TTP Specialist Centres alongside the traditional ELISA method to confirm severe ADAMTS13 deficiency. Methods: A multi-centre retrospective case-control study was performed to review patients demonstrating discrepant ADAMTS13 activity results measured using rapid (AcuStar®) and ELISA assays in parallel from September 2019 to December 2021. Cases were compared with a cohort of suspected TTP patients exhibiting no difference in assay results and in relation to their presenting characteristics and pre-test probability of a diagnosis of TTP. Results: Where the clinical index of suspicion for TTP was high at presentation, acute TTP was confirmed using the AcuStar® assay < 0.2 IU/dL and subsequently < 10 IU/dL by ELISA with zero incidence of discrepancy. For patients with low clinical suspicion of acute TTP, a discrepancy between the AcuStar® and ELISA assay results was observed in 2% of cases; 5-10 IU/dL in AcuStar®, confirmed as >20 IU/dL by ELISA. A concurrent cancer diagnosis or sepsis was observed in 40% of discrepant cases. Conclusions: Where acute TTP is strongly suspected, there is a good correlation between the rapid AcuStar® ADAMTS13 assay and the conventional ELISA assay. Where the clinical suspicion of acute TTP is low, caution should be exercised in the interpretation of the ADAMTS13 activity using the AcuStar® assay. Accurate interpretation requires robust ADAMTS13 testing algorithms to be incorporated into diagnostic pathways.

Clinical and economic burden of suspected thrombotic thrombocytopenic purpura in US hospitals.

In an effort to expedite the publication of articles, AJHP is posting manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time. Severe ADAMTS13 deficiency (activity <10%) is the diagnostic threshold for thrombotic thrombocytopenic purpura (TTP) and is associated with various clinical symptoms, abnormal laboratory results, and long-term complications. This retrospective, noninterventional cohort study used the Premier Healthcare Database to identify patients with ADAMTS13 activity of <10% in US hospitals from January 1, 2016, through March 31, 2020. The objective was to describe patient characteristics, laboratory results, comorbidities (as measured by the Elixhauser comorbidity index), symptoms, length of stay, treatment patterns, mortality, inpatient costs, and readmission rates (summarized descriptively). Inpatient costs were calculated as total cost to the hospital. There were 211 patients with severe ADAMTS13 deficiency; 89% of patients had a TTP-related diagnosis, of whom 62% had a primary diagnosis of thrombotic microangiopathy. Over 80% of patients with available data had a decreased platelet count and elevated lactate dehydrogenase; schistocytes were detected in 99%. The most prevalent symptoms/complications were neurological, bleeding, and pain. Most patients (86%) had 2 or more Elixhauser comorbidities. Over 80% of patients received 1 or more TTP-related treatments, mostly plasma exchange. The mean length of stay was 11.5 days; 5% of patients died during their stay. Readmission rates at 30, 60, and 90 days were 20%, 26%, and 28%, respectively. The median (interquartile range) total inpatient cost to the hospital throughout the index admission was $33,221 ($19,431-$64,901). Patients with severe ADAMTS13 deficiency have substantial clinical burden, have high mortality and readmission rates, and generate high costs for hospitals. There is a high need for a therapy that replaces ADAMTS13, thus addressing the root cause of the symptoms and complications caused by this deficiency.

Lupus nephritis and thrombotic microangiopathy: A review

Lupus nephritis (LN) is one of the most common organ-specific manifestations of systemic lupus erythematosus (SLE). Various clinical signs of LN develop in at least 50% of patients with SLE. In addition to LN, the spectrum of renal lesions associated with SLE also includes vascular pathology. One of the variants of renal microvascular injury is thrombotic microangiopathy (TMA), the mechanisms of which are diverse. The review focuses on the main forms of TMA, including antiphospholipid syndrome and nephropathy associated with antiphospholipid syndrome, TMA caused by complement system regulation disorders and deficiency of ADAMTS13. In most cases, these forms of TMA are combined with LN. However, they may also exist as a single form of kidney damage. This article discusses the TMA pathogenesis, the impact on kidney prognosis, and treatment options.

Risk factors of death or chronic renal replacement therapy requirements in patients with thrombotic microangiopathies without ADAMTS-13 deficiency.

Thrombotic microangiopathy (TMA), characterized by microangiopathic hemolytic anemia, thrombocytopenia, and multisystem organ dysfunction, is a life-threatening disease. Patients with TMA who do not exhibit a severe ADAMTS-13 deficiency (defined as a disintegrin-like and metalloprotease with thrombospondin type 1 motif no. 13 activity ≥10%: TMA-13n) continue to experience elevated mortality rates. This study explores the prognostic indicators for augmented mortality risk or necessitating chronic renal replacement therapy (composite outcome: CO) in TMA-13n patients. We included 42 TMA-13n patients from January 2008 to May 2018. Median age of 41 years and 60% were female. At presentation, 62% required dialysis, and 57% warranted intensive care unit admission. CO was observed in 45% of patients, including a 9-patient mortality subset. Multivariate logistic regression revealed three independent prognostic factors for CO: early administration of eculizumab (median time from hospitalization to eculizumab initiation: 5 days, range 0-19 days; odds ratio [OR], 0.14; 95% confidence interval [CI], 0.02-0.94), presence of neuroradiological lesions (OR, 6.67; 95% CI, 1.12-39.80), and a PLASMIC score ≤4 (OR, 7.39; 95% CI, 1.18-46.11). In conclusion, TMA-13n patients exhibit a heightened risk of CO in the presence of low PLASMIC scores and neuroradiological lesions, while early eculizumab therapy was the only protective factor.

Genetic variants contribute to modulation of renal function in patients with immune thrombotic thrombocytopenic purpura

AbstractImmune thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal blood disorder, resulting from autoantibodies against ADAMTS13. However, the contribution of genetic variations that may modulate its clinical presentations remains unknown. This study aimed to determine the potential contribution of variants in the genes associated with coagulation, complement activation or regulation, and platelet activation to pathophysiology of iTTP. Multicenter case series, whole-exome sequencing, and bioinformatic approaches were used. We focused on analysis of 20 genes that are involved in regulation of coagulation (eg, ADAMTS13, THBD, MMACHC, INF2, and PLG), complement activation (eg, C3, C3AR1, C5, CFB, CFH, CFI, C4BPA, CD46 [MCP], CD59, and CFHR1-CFHR5), and platelet activation (eg, DGKE) from 40 adult patients with iTTP. Multiple genetic variations were identified in 12 of 20 genes of interest. More than 80% of patients harbored genetic variants in CFI, CFH, C5, and ADAMTS13; 15% to 55% of patients had variants in C3, INF2, CFHR5, and PLG; and <10% of patients had variants in CD46, C3AR1, DGKE, and THBD. Of these, the variants in C5 are associated with a more favorable renal function, whereas the variants in DGKE are associated with more persistently elevated creatinine levels. These results demonstrate that variants in the genes involved in coagulation, complement, and platelet activation are common in patients with iTTP, which may contribute to phenotypical modulations of or predispose to iTTP resulting from severe ADAMTS13 deficiency.

Vascular endothelial-cadherin is involved in endothelial cell detachment during thrombotic thrombocytopenic purpura

BackgroundImmune thrombotic thrombocytopenic purpura (i-TTP) is a life-threatening thrombotic microangiopathy linked to ADAMTS-13 deficiency. It has long been assumed that the activation of endothelial cells is the triggering factor for the thrombotic thrombocytopenic purpura crisis. Circulating endothelial cells (CECs) have been shown to be a biomarker of vascular damage and are associated with the clinical severity of i-TTP. However, the mechanisms leading to endothelial cell detachment remain unclear. ObjectivesWe investigated junctional destabilization the mechanisms underlying cell detachment in thrombotic thrombocytopenic purpura. MethodsWe quantified CECs in i-TTP patients and investigated the effect of plasmas in vitro by measuring phosphorylation and internalization of vascular endothelial (VE)-Cadherin and in vivo in a vascular permeability model. ResultsIn plasma from i-TTP patients, we show that CEC count is associated with severity and correlated to intracellular calcium influx (P < .01). In vitro, serum from i-TTP patients induced stronger detachment of human umbilical vein endothelial cells than serum from control patients (P < .001). Plasma from i-TTP patients induced a higher calcium-dependent phosphorylation (P < .05) and internalization (P < .05) of VE-cadherin compared with plasma from control patients. This effect could be reproduced by immunoglobulin (Ig)G fraction isolated from patient plasma and, in particular, by the F(ab)’2 fragments of the corresponding IgG. In addition, subcutaneous injection of i-TTP plasma into mice resulted in higher vascular permeability than plasma from control patients. An inhibitor of endothelial calcium influx, ITF1697, normalized this increase in permeability. ConclusionOur results suggest that plasma-induced endothelial activation also leads to an increase in vascular permeability. They contribute to the understanding of the mechanisms behind the presence of elevated CECs in patients' blood by linking endothelial activation to endothelial injury.

Immune Thrombotic Thrombocytopenic Purpura: Pathophysiology, Diagnosis, Therapy and Open Issues.

Immune thrombotic thrombocytopenic purpura (iTTP) is a life-threatening thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, thrombocytopenia, and ischemic end-organ injury due to microvascular platelet-rich thrombi. iTTP pathophysiology is based on a severe ADAMTS13 deficiency, the specific von Willebrand factor (vWF)-cleaving protease, due to anti-ADAMTS13 autoantibodies. Early diagnosis and treatment reduce the mortality. Frontline therapy includes daily plasma exchange (PEX) with fresh frozen plasma replacement and immunosuppression with corticosteroids. Caplacizumab has recently been added to frontline therapy. Caplacizumab is a nanobody that binds to the A1 domain of vWF, blocking the interaction of ultra-large vWF multimers with the platelet and thereby preventing the formation of platelet-rich thrombi. Caplacizumab reduces mortality due to ischemic events, refractoriness, and exacerbations after PEX discontinuation. Until now, the criteria for response to treatment mainly took into account the normalization of platelet count and discontinuation of PEX; with the use of caplacizumab leading to rapid normalization of platelet count, it has been necessary to redefine the response criteria, taking into account also the underlying autoimmune disease. Monitoring of ADAMTS13 activity is important to identify cases with a low value of activity (<10IU/L), requiring the optimization of immunosuppressive therapy with the addition of Rituximab. Rituximab is effective in patients with refractory disease or relapsing disease. Currently, the use of Rituximab has expanded, both in frontline treatment and during follow-up, as a pre-emptive approach. Some patients do not achieve ADAMTS13 remission following the acute phase despite steroids and rituximab treatment, requiring an individualized immunosuppressive approach to prevent clinical relapse. In iTTP, there is an increased risk of venous thrombotic events (VTEs) as well as arterial thrombotic events, and most occur after platelet normalization. Until now, there has been no consensus on the use of pharmacological thromboprophylaxis in patients on caplacizumab because the drug is known to increase bleeding risk.

Management of immune thrombotic thrombocytopenic purpura without therapeutic plasma exchange

AbstractImmune thrombotic thrombocytopenic purpura (iTTP) is a rare, life-threatening autoimmune disorder caused by a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13) deficiency. Caplacizumab, an anti–von Willebrand factor nanobody, is approved for iTTP treatment, reducing the need for therapeutic plasma exchange (TPE) and improving platelet count recovery and survival. We conducted a retrospective study on 42 acute iTTP cases in Austria and Germany, treated with a modified regimen aimed at avoiding TPE if platelet count increased after the first caplacizumab dose. Baseline characteristics and patient outcomes were compared with a control group of 59 patients with iTTP receiving frontline treatment with TPE, caplacizumab, and immunosuppression. The main outcome was the time to platelet count normalization. Secondary outcomes included clinical response, exacerbation, refractory iTTP, iTTP-related deaths, and the time to platelet count doubling. The median time to platelet count normalization was similar between the 2 cohorts (3 and 4 days; P = .31). There were no significant differences in clinical response, exacerbations, refractoriness, iTTP-related deaths, or time to platelet count doubling, reflecting the short-term treatment response. Four patients did not respond to the first caplacizumab dose, and TPE was subsequently initiated. Cytomegalovirus infection, HIV/hepatitis B virus coinfection, an ovarian teratoma with associated antiplatelet antibodies, and multiple platelet transfusions before the correct diagnosis may have impeded the immediate treatment response in these patients. In conclusion, caplacizumab and immunosuppression alone, without TPE, rapidly controlled thrombotic microangiopathy and achieved a sustained clinical response in iTTP. Our study provides a basis for TPE-free iTTP management in experienced centers via shared decision-making between patients and treating physicians.

The history of thrombotic thrombocytopenic purpura research: a narrative review.

Thrombotic thrombocytopenic purpura (TTP) is a rare but debilitating thrombotic microangiopathy that results from severe deficiency of the enzyme ADAMTS13. The disorder was first described in the early 20th century, but the pathophysiology of the disease has only been elucidated in the past three decades. In this narrative review, we will summarize the milestone moments in the history of TTP research and discovery. We searched literature using PubMed from 1924 to 2023 using the following free text searches: "thrombotic thrombocytopenic purpura", "Moschcowitz disease", and "thrombotic microangiopathy". We found 6,917 peer-reviewed articles and sorted through these for relevant literature pertinent to the review. A total of 46 articles were included for review and the remainder were excluded. The history of TTP research was reviewed, with a sampling of major events in the evolution of the understanding of the pathophysiology and treatment of the disease discussed here. There remains much to be learned about the nature of the disease in order to develop more specific and less harmful treatments. An overview of the major discoveries that have led to our current understanding of TTP reveals the results of collaboration of multiple groups of physicians and scientists through the past century, with additional breakthroughs likely to occur in the future because of that same collaborative spirit.

#1491 Management of immune thrombotic thrombocytopenic purpura without therapeutic plasma exchange

Abstract Background and Aims Immune thrombotic thrombocytopenic purpura (iTTP) is a rare, life-threatening autoimmune disorder caused by ADAMTS13 deficiency. The anti-VWF nanobody Caplacizumab is approved for iTTP treatment, reducing the need for therapeutic plasma exchange (TPE) and improving platelet recovery and survival. This study evaluates the treatment of acute iTTP with caplacizumab and immunosuppression, but without TPE, in comparison to the conventional management with TPE, caplacizumab and immunosuppression. Method All patients in this study were identified from the Austrian Thrombotic Microangiopathy Registry (ATMAR) and the German REACT-2020 TTP registry (ClinicalTrials.gov identifier: NCT04985318). A total of 42 acute iTTP episodes in 41 patients were managed with a treatment regimen aimed at avoiding first-line TPE if the platelet count increased after the first dose of 10 mg caplacizumab, and the patient's condition and organ function remained stable (TPE-free cohort). This treatment modification was implemented based on shared decision making. An extensive efficacy and safety analysis of this approach was performed, in comparison with a control group of 59 iTTP patients, receiving frontline caplacizumab treatment with TPE and immunosuppression (TPE cohort). The main outcome was time to platelet count normalization. Secondary outcomes included clinical response, exacerbation, refractoriness, and iTTP-related deaths. Results The primary outcome parameter, time to platelet count normalization, was not significantly different between TPE-free and TPE-based management (Kaplan-Meier estimator and log-rank test, Table 1 and Fig. 1). The median time to platelet count normalization was 3 days in the TPE-free cohort and 4 days in the TPE cohort. There were no significant differences in clinical response, exacerbations, refractoriness, or iTTP-related deaths. For evaluation of the short-term treatment response, both cohorts were assessed for the time to platelet count doubling. The median time to platelet count doubling was 1 day in both cohorts. Four patients in the TPE-free cohort did not immediately respond to the first caplacizumab injection and subsequently underwent TPE, after a maximum monitoring period of 40 hours. In these patients, TPE was initiated at a median of 1.5 days after the first caplacizumab dose, and TPE was performed for a median of 4.5 days. This delayed platelet response could be attributed to concomitant diseases and factors, e.g. active HIV and hepatitis B virus coinfection, active CMV infection, concomitant antiplatelet antibodies in association with an ovarian teratoma, and multiple platelet transfusions before the correct diagnosis. During overall follow-up, complications were observed in 11 patients (26.2%) in the TPE-free group and 16 patients (27.1%) in the TPE group, excluding complications of iTTP that were evaluated as outcome parameters. Serious complications occurred in 4 patients (6.8%) from the TPE cohort while on TPE, including severe systemic anaphylactic reactions with severe hypotension, generalized seizure and supraventricular tachycardia. Bleeding complications were reported without a significant difference between groups. Conclusion For the first time since the introduction of TPE in the early 1990s, the results of our study systematically challenge the absolute need for TPE and suggest a paradigm shift in acute iTTP management. In detail, our treatment approach was successfully implemented in 38 of 42 acute iTTP episodes (90.5%). We observed no significant difference in the time to platelet count normalization between patients with iTTP treated with and without TPE. The analysis of key secondary outcomes did not reveal significant differences in the proportion of patients who achieved a clinical response or experienced exacerbations, refractoriness, or TTP-related deaths. In conclusion, Caplacizumab and immunosuppression, without TPE, rapidly controlled microvascular thrombosis and achieved a sustained clinical response in iTTP.

Recombinant ADAMTS13 in Congenital Thrombotic Thrombocytopenic Purpura

BackgroundCongenital thrombotic thrombocytopenic purpura (TTP) results from severe hereditary deficiency of ADAMTS13. The efficacy and safety of recombinant ADAMTS13 and standard therapy (plasma-derived products) administered as routine prophylaxis or on-demand treatment in patients with congenital TTP is not known.MethodsIn this phase 3, open-label, crossover trial, we randomly assigned patients in a 1:1 ratio to two 6-month periods of prophylaxis with recombinant ADAMTS13 (40 IU per kilogram of body weight, administered intravenously) or standard therapy, followed by the alternate treatment; thereafter, all the patients received recombinant ADAMTS13 for an additional 6 months. The trigger for this interim analysis was trial completion by at least 30 patients. The primary outcome was acute TTP events. Manifestations of TTP, safety, and pharmacokinetics were assessed. Patients who had an acute TTP event could receive on-demand treatment.ResultsA total of 48 patients underwent randomization; 32 completed the trial. No acute TTP event occurred during prophylaxis with recombinant ADAMTS13, whereas 1 patient had an acute TTP event during prophylaxis with standard therapy (mean annualized event rate, 0.05). Thrombocytopenia was the most frequent TTP manifestation (annualized event rate, 0.74 with recombinant ADAMTS13 and 1.73 with standard therapy). Adverse events occurred in 71% of the patients with recombinant ADAMTS13 and in 84% with standard therapy. Adverse events that were considered by investigators to be related to the trial drug occurred in 9% of the patients with recombinant ADAMTS13 and in 48% with standard therapy. Trial-drug interruption or discontinuation due to adverse events occurred in no patients with recombinant ADAMTS13 and in 8 patients with standard therapy. No neutralizing antibodies developed during recombinant ADAMTS13 treatment. The mean maximum ADAMTS13 activity after recombinant ADAMTS13 treatment was 101%, as compared with 19% after standard therapy.ConclusionsDuring prophylaxis with recombinant ADAMTS13 in patients with congenital TTP, ADAMTS13 activity reached approximately 100% of normal levels, adverse events were generally mild or moderate in severity, and TTP events and manifestations were rare. (Funded by Takeda Development Center Americas and Baxalta Innovations; ClinicalTrials.gov number, NCT03393975.)

Clinical Profile, Treatment and Outcome of Thrombotic Thrombocytopenia Purpura (TTP) in Rituximab Era- an Experience from Tertiary Care Centre from North India.

Thrombotic thrombocytopenic purpura (TTP) is a microangiopathic hemolytic anemia (MAHA) resulting from severe deficiency of ADAMTS13. TTP is an acute medical emergency which requires early treatment with therapeutic plasma exchange. With the early use of Rituximab along with PLEX, early response is achieved and relapse rate has gone down. There is lack of published data from India regarding treatment and outcome of TTP. We retrospectively analyzed our data of 21 patients of TTP including 4 patients who had TA-TMA. TTP patients were treated with TPE, pulse methylprednisolone and rituximab. After a median follow up of 57.5months overall survival in TTP patients was 82.3% in our study and one patient relapsed twice but again responded to same treatment. Relapse free survival was 92.8%. The mortality rate in our study in TTP patients was (3/17) 17.6%. The total response rate was 82.3% (14/17). Out of 4 patients of TA-TMA, Only 33.3% patients responded to plasma exchange in TA-TMA while two patients died (2/4) 50%. Immediate TPE and early rituximab are associated with improved survival in TTP patients, however TA-TMA still remains a significant challenge for transplant physicians and more research is needed in guiding the therapy.

Pathological Mechanisms and Novel Testing Methods in Thrombotic Thrombocytopenic Purpura.

Thrombotic thrombocytopenic purpura (TTP) is an uncommon, but potentially disabling or even deadly, thrombotic microangiopathy with a well-studied mechanism of ADAMTS13 deficiency or dysfunction. While established treatments are largely effective, the standard ADAMTS13 testing required to definitively diagnose TTP may cause delays in diagnosis and treatment, highlighting the need for rapid and effective diagnostic methods. Additionally, the heterogeneous presentation and varied inciting events of TTP suggest more variation in its mechanism than previously thought, implying three potential pathways rather than the accepted two. The recent discovery of ADAMTS13 conformation as a potential contributor to TTP in addition to the proposal of using the absolute immature platelet count (A-IPC) as a biomarker, present novel areas for monitoring and treatment. A-IPC in particular may serve as a more rapid and accurate diagnostic test to distinguish TTP from non-TTP TMAs and to monitor treatment response and relapse. These considerations highlight the need to further study TTP in order to improve best practices and patient care.

Mean platelet volume and platelet distribution width in the prediction of treatment response in immune thrombotic thrombocytopenic purpura with severe ADAMTS13 deficiency: a multicenter study

Mean platelet volume and platelet distribution width in the prediction of treatment response in immune thrombotic thrombocytopenic purpura with severe ADAMTS13 deficiency: a multicenter study

Le PTT, une microangiopathie thrombotique de l’hémostase

AbstractThrombotic thrombocytopenic purpura is characterized by a severe deficiency in ADAMTS13 (A disintegrin and metalloprotease with a thromboSpondin type 1 repeats, member 13) activity, lower than 10%. This disease involves Von Willebrand Factor (VWF), which is not cleaved by ADAMTS13. Deficiency is mainly acquired, due to anti-ADAMTS1 3 antibodies (iPTT). Mechanical haemolytic anemia, thrombocytopenia due to consumption and thrombosis in microvessels are observed. The diagnosis should be quickly discussed and confirmed by the measurement of ADAMTS13 activity. Pending the results of this marker, clinicians can use scores with high positive predictive values, which help them rapidly introduce replacement therapies, given the poor prognosis of TTP in the absence of treatment. Caplacizumab is also used as a first-line treatment to limit the formation of microthrombi, pending the efficacy of immunosuppressive treatments started at the same time. Specialized management and long-term follow-up of patients is crucial to evaluate sequelae and to predict relapses.

Diagnosis and clinical management of thrombotic thrombocytopenic purpura (TTP): a consensus statement from the TTP Catalan group.

Thrombotic thrombocytopenic purpura (TTP) is a low prevalence disease characterized by severe deficiency of the enzyme ADAMTS13, leading to the development of thrombotic microangiopathy (TMA) and often resulting in severe organ disfunction. TTP is an extremely serious condition and, therefore, timely and appropriate treatment is critical to prevent life-threatening complications.Over the past 25 years, significant advances in the understanding of the pathophysiology of immune TTP have led to the development of readily available techniques for measuring ADAMTS13 levels, as well as new drugs that are particularly effective in the acute phase and in preventing relapses. These developments have improved the course of the disease.Given the complexity of the disease and its various clinical and laboratory manifestations, early diagnosis and treatment can be challenging.To address this challenge, a group of experienced professionals from the Catalan TTP group have developed this consensus statement to standardize terminology, diagnosis, treatment and follow up for immune TTP, based on currently available scientific evidence in the field. This guidance document aims to provide healthcare professionals with a comprehensive tool to make more accurate and timely diagnosis of TTP and improve patient outcomes.

Plasmin-cleaved von Willebrand factor as a biomarker for microvascular thrombosis

Abstractvon Willebrand factor (VWF) is an essential contributor to microvascular thrombosis. Physiological cleavage by ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) limits its prothrombotic properties, explaining why ADAMTS13 deficiency leads to attacks of microthrombosis in patients with thrombotic thrombocytopenic purpura (TTP). We previously reported that plasminogen activation takes place during TTP attacks in these patients. Furthermore, stimulation of plasminogen activation attenuates pathogenesis in preclinical TTP models in vivo. This suggests that plasmin is an endogenous regulator of VWF thrombogenicity, in particular when ADAMTS13 falls short to prevent microvascular occlusions. VWF cleavage by plasmin is biochemically distinct from cleavage by ADAMTS13. We hypothesized that plasmin-cleaved VWF (cVWF) holds value as a biomarker of microvascular thrombosis. Here, we describe the development of a variable domain of heavy-chain-only antibody (VHH)-based bioassay that can distinguish cVWF from intact and ADAMTS13-cleaved VWF in plasma. We validate this assay by tracking cVWF release during degradation of microthombi in vitro. We demonstrate that endogenous cVWF formation takes place in patients with TTP during acute attacks of thrombotic microangiopathy but not in those in remission. Finally, we show that therapeutic plasminogen activation in a mouse model of TTP amplifies cVWF formation, which is accompanied by VWF clearance. Our combined findings indicate that cVWF is released from microthrombi in the context of microvascular occlusion.