ADAMTS13 Deficiency Research Articles

Recombinant ADAMTS13 for the Treatment of Acute TTP Events in Patients with Congenital Thrombotic Thrombocytopenic Purpura: Results from the Phase 3 Randomized, Controlled, Crossover Study and the Phase 3b Continuation Study

Background Congenital thrombotic thrombocytopenic purpura (cTTP) is an ultra-rare, life-threatening thrombotic microangiopathy caused by an inherited deficiency of the enzyme ADAMTS13. An ongoing phase 3 study (NCT03393975) and phase 3b continuation study (NCT04683003) are investigating the safety and efficacy of recombinant ADAMTS13 (rADAMTS13; TAK-755; Takeda Development Center Americas, Inc., Lexington, MA, USA) for prophylaxis and on-demand treatment of acute events in patients with cTTP. Aims To assess the efficacy and safety of rADAMTS13 for the treatment of acute TTP events and long-term prophylaxis in patients with severe cTTP. Methods The phase 3 prospective, randomized, controlled, open-label, multicenter, crossover study (NCT03393975) is open to enroll patients 0-70 years old with severe cTTP (ADAMTS13 activity <10%). Upon completion of the phase 3 study, patients could enroll into the phase 3b prospective, open-label, multicenter, single treatment arm continuation study (NCT04683003). In the phase 3 study, patients were randomized 1:1 at enrollment to receive prophylaxis with either rADAMTS13 or standard of care (SoC). SoC was determined by the treating physician and could include fresh frozen plasma, pooled solvent/detergent-treated plasma, or factor VIII/von Willebrand factor concentrates. Patients in the phase 3b continuation study received open-label rADAMTS13 treatment. In both studies, patients could be enrolled and receive treatment on demand for acute TTP events. Per protocol, rADAMTS13 was to be administered at 40 IU/kg on Day 1, 20 IU/kg on Day 2 and 15 IU/kg daily from Day 3 onwards until 2 days after resolution of the acute event (defined as platelet count either ≥150,000/μL or within 25% of baseline; and elevation of LDH levels ≤1.5× of baseline or ≤1.5× the upper limit of normal). Data are presented from a pre-planned interim analysis (data cutoff: August 12, 2022) and focus on the treatment of acute TTP events in both studies. Results At the time of the data cutoff, 8 acute TTP events were reported in 7 patients ( Table), all of whom were ≥18 years old. None of the events occurred while the patient was receiving rADAMTS13 prophylaxis. Six events occurred in 5 patients (median age: 20.0 years; sex: 3 male, 2 female) who received on-demand treatment in the phase 3 study; 2 of these patients were randomized to receive rADAMTS13 and 3 to receive SoC. One event also occurred in the phase 3 study while the patient was receiving prophylaxis with SoC. One event occurred in the screening period prior to the patient starting rADAMTS13 prophylaxis in the phase 3b continuation study; this event was treated with rADAMTS13. Platelet counts observed during the first 3 days of treatment for all 8 acute TTP events are shown in the Figure. Prior to study treatment, on Day 0, the mean platelet counts were similar between the rADAMTS13 and SoC cohorts. Over the first 3 treatment days, the mean platelet count increased more than ~5-fold with rADAMTS13, and ~3-fold with SoC. All three acute TTP events treated with rADAMTS13 resolved without requiring the administration of any other treatment containing ADAMTS13. Based on pharmacokinetics (PK) data available in 5 patients (3 received treatment with rADAMTS13 and 2 with SoC), the post-infusion ADAMTS13 activity levels ~1 hour after administration were between 80% to 270% of normal with rADAMTS13 and between 10% to 48% with SoC. These observed ADAMTS13 activity levels were as expected based on the linear PK observed following single dose PK assessments in the phase 3 study. Of the 4 patients who received SoC for the treatment of an acute TTP event, 2 experienced a mild treatment-emergent adverse event (TEAE) that was considered related to the SoC (nausea and pruritis). Of the 3 patients who received rADAMTS13, 1 patient experienced 3 mild TEAEs (feeling hot, nausea, and thrombocytosis) that were considered related to rADAMTS13. No serious TEAEs related to rADAMTS13 were reported and no neutralizing antibodies against ADAMTS13 were observed. Conclusions The resolution of acute TTP events and an improvement in platelet count in patients with cTTP following treatment with rADAMTS13 was closely related to higher ADAMTS13 activity exposure. No serious TEAEs related to rADAMTS13 were reported.

Caplacizumab Frontline Added to Therapeutic Plasma Exchange and Immunosuppression Prevents Unfavorable Outcomes in Immune-Mediated TTP: An International Real-World Study of the TTP-IWG (The Capla 500 Project)

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) results from autoantibody-mediated severe deficiency of ADAMTS13, the Von Willebrand factor (VWF)-cleaving protease. In this context, ultra-large VWF multimers accumulate in the circulation, leading to increased platelet clumping, with subsequent severe thrombocytopenia, microangiopathic hemolytic anemia and multiorgan failure. The anti-VWF nanobody caplacizumab is licensed for adults with iTTP. Prospective controlled trials and national real-world studies have provided evidence that caplacizumab improved outcome of the acute phase of the disease. However, whether caplacizumab decreases mortality, and the optimal timing of caplacizumab initiation, remain to be determined. To address these questions, an international survey, the Capla 500+ project, has been conducted. An academic call for observations involving experienced teams from 10 worldwide countries recruited 942 adult patients treated with a regimen of daily therapeutic plasma exchange (TPE), caplacizumab and immunosuppression with corticosteroids ± rituximab (caplacizumab group). Cases were compared to historic controls (control group) randomly selected from 2015 to 2018 by 4 teams in a 2:1 ratio (N=495), treated with TPE and immunosuppression. Primary outcome was 3-month survival post-first TPE. Key secondary outcomes were refractoriness and exacerbations, time to clinical response, number of TPE to achieve clinical response, time to ADAMTS13 activity recovery ≥20%, and caplacizumab-related adverse events. Clinical presentation and severity were comparable between groups ( Table). All patients received TPE in both caplacizumab and control groups, in association with corticosteroids (99% and 93%, respectively), and rituximab (92% and 71%, respectively) frontline or as salvage therapy. Caplacizumab was started within 3 days (715 patients), or delayed by≥4 days from first TPE (218 patients); for those with delayed initiation, caplacizumab was added for management of exacerbation or refractoriness (63 cases) or a slow improvement to TPE/immunosuppression (155 cases). The 3-month survival post-first TPE in the caplacizumab group was 98.6% vs 93.3% in the control group (p<0.0001). Failure to achieve clinical response was 5-times less likely in the caplacizumab group as compared to the control group (95% confidence interval, 0.1-0.37, p<0.0001). Deaths in the caplacizumab group occurred after a median of 4.5 days (interquartile range [IQR], 3-5), mostly due to uncontrolled iTTP. Patients receiving caplacizumab experienced less refractoriness and exacerbations, and required less TPE to achieve clinical remission than controls (p<0.0001 for all), regardless of the use of rituximab. Forty-six patients experienced an exacerbation following caplacizumab interruption while ADAMTS13 activity was still undetectable. Time to ADAMTS13 activity ≥20% was shorter in the caplacizumab group (p=0.01) ( Table), where rituximab was more systematically used. In patients with delayed caplacizumab initiation, clinical response was obtained after a median of 4 days (IQR, 2-8) following caplacizumab introduction. This result was comparable to the time to clinical response obtained in patients who initiated caplacizumab within 3 days of the first TPE (median, 4 days [IQR, 3-6], p=0.8). In patients with early caplacizumab initiation, unfavorable outcomes were particularly infrequent (death, 1%; refractoriness, 1.1%; exacerbations, 5.3%),andtime to clinical response in survivors was half the time compared to control group survivors (p<0.0001) ( Figure). Caplacizumab-related adverse events occurred in 220 patients (23%). They consisted of major bleeding (N=19, 2.2%), including: digestive tract bleeding (N=8), intracranial hemorrhage, severe central venous catheter insertion bleeding, metrorrhagia (N=2 cases each). Clinically relevant non-major bleeding (N=34, 3.7%), non-clinically relevant non-major bleeding (N=114, 14%), and inflammatory reaction at the injection site (N=35, 4.5%) were also reported. This unprecedented, international academic effort on such a rare disease provides convincing evidence that caplacizumab added to TPE and immunosuppression prevents unfavorable outcomes during the acute phase of iTTP, including mortality, and alleviates the burden of care at the potential expense of rare, major bleeding events.

Population Pharmacokinetics and Exposure-Response Analyses to Demonstrate the Link of Causality between ADAMTS13 and the Clinical Effects of Recombinant ADAMTS13 Compared to Plasma-Based Therapies

Background: Congenital thrombotic thrombocytopenic purpura (cTTP) is an ultra-rare, life-threatening deficiency of ADAMTS13. TTP clinical manifestations include thrombocytopenia and microangiopathic hemolytic anemia (MAHA) but incomplete understanding of their relationship to ADAMTS13 exposure is a challenge for assessing the impact of ADAMTS13 supplementation. Integrated population pharmacokinetics (PopPK) analysis and exposure-response modeling were conducted to support the clinical benefit assessment of recombinant ADAMTS13 (rADAMTS13; Takeda Development Center Americas, Inc., Lexington, MA, USA) in patients with cTTP. Aims: To characterize ADAMTS13 activity following intravenous (IV) administration of rADAMTS13 or plasma-based therapies (PBT) in patients with cTTP, to identify sources of variability, and to evaluate the relationship between ADAMTS13 activity and the probability of isolated TTP manifestations. Methods:The PopPK analysis included data from phase 1 (NCT02216084), pivotal phase 3 (NCT03393975), and phase 3b continuation (NCT04683003) studies of rADAMTS13. Exposure-response analyses included data from NCT03393975 where patients received rADAMTS13 or PBT in prophylaxis treatment period 1 and crossed over to the opposite treatment in period 2. PBT consisted of fresh frozen plasma, solvent/detergent-treated plasma or factor VIII/von Willebrand factor concentrates. A covariate analysis was conducted to identify sources and assess the significance of variability on the PK of ADAMTS13 activity. Exposure-response models were developed to assess the relationship between the average ADAMTS13 plasma activity for a given dosing interval (C ave) and the count of isolated TTP manifestations: thrombocytopenia (platelet count decreased ≥25% of baseline or a platelet count <150,000/µL) or MAHA (increased lactate dehydrogenase >1.5 × of baseline or >1.5 × upper limit of normal). Cox proportional hazard modeling using recurring events was performed to demonstrate the treatment effect of rADAMTS13 over PBT, and explain carry-over prophylactic effects. Repeated time to event was performed using longitudinal data from all periods to demonstrate ADAMTS13-dependent reduction in the hazard of thrombocytopenia. Results: A 2-compartment PK model with linear elimination adequately characterized the time profiles of ADAMTS13 activity following body-weight-based IV administration of rADAMTS13 or PBT (N=65 patients). Following body-weight-based dosing, dosing interval (once per week [Q1W] vs every 2 weeks [Q2W]) and treatment type (rADAMTS13 vs PBT) were the only significant extrinsic factors found with an impact on ADAMTS13 PK. ADAMTS13 C ave was associated with a significant reduction of the thrombocytopenia hazard in an activity-dependent manner (Figure). Exposure-response model simulations suggested that >95% of patients treated with rADAMTS13 are predicted to have plasma C ave ADAMTS13 >0.13 IU/mL (equivalent to 13% activity), with high (>70%) protection against thrombocytopenia regardless of dosing intervals (Q2W or Q1W) and age. In contrast, a similar level of protection against thrombocytopenia is expected in only ~10% of patients treated with PBT (Table). Similarly, a significant exposure-response relationship was identified between ADAMTS13 C ave and MAHA.In treatment period 1, rADAMTS13 was associated with a higher probability of zero counts of thrombocytopenia versus PBT from week 2 onwards. Patients switching from rADAMTS13 to PBT in period 2 initially had a slightly higher probability of having zero counts of thrombocytopenia than patients switching from PBT to rADAMTS13, suggesting that treatment with rADAMTS13 led to a carry-over prophylactic effect maintained for some time after treatment cessation. Conclusions: Besides body-weight-based dosing, no additional dose adjustments of rADAMTS13 are needed in the cTTP patient population. A consistent and significant ADAMTS13 activity-response relationship was identified in which rADAMTS13 reduced the hazard of objective laboratory based TTP manifestations (thrombocytopenia and MAHA) in an activity-dependent manner. Overall, these findings suggest that rADAMTS13 at 40 IU/kg Q2W or Q1W offers a favorable prophylactic treatment effect over PBT that is attributable to higher ADAMTS13 activity.

Insight into the Natural History of Hereditary Thrombotic Thrombocytopenic Purpura: Short- and Long-Term Outcomes in a Longitudinally Followed Large Patient Cohort of the International Hereditary TTP Registry

Background: Hereditary thrombotic thrombocytopenic purpura (hTTP), also known as Upshaw-Schulman syndrome, is an ultra-rare, thrombotic microangiopathy resulting from bi-allelic ADAMTS13 mutations and severe congenital ADAMTS13 deficiency. Clinical presentation includes thrombocytopenia, hemolytic anemia and symptoms of organ ischemia (primarily of brain, heart, gastrointestinal tract and kidneys) during acute episodes and pregnancy complications, but less explicit symptoms (abdominal discomfort, headaches, neurocognitive problems or fatigue) responding to plasma therapy are also common. Standard of care consists of replenishing ADAMTS13 using plasma/plasma-derived blood products to treat acute episodes as well as prophylactically to prevent morbidity and mortality. Improvement of hTTP disease management requires better understanding of the treatment burden and possible shortcomings as well as short- and long-term clinical outcomes. Aims: Description of the natural history of hTTP in a prospectively followed large patient cohort with a focus on demographic and clinical characteristics, as well as on the occurrence of acute TTP episodes, comorbidities and mortality. Methods: Eligible for the current study were patients with a confirmed hTTP diagnosis (lasting ADAMTS13 activity <10%, bi-allelic ADAMTS13 mutations, and exclusion of acquired, autoimmune TTP) enrolled before December 31, 2021. In an ambidirectional approach, the registry assesses the patients' detailed medical history at enrollment (retrospective data) and then prospective clinical, molecular and observational data through questionnaires completed by treating physicians during annual visits or at occurrence of acute TTP episodes. Patients were followed by the International hTTP Registry until December 31, 2022 (end of current analysis), death, or loss to follow-up, whichever occurred first and results were reported using descriptive statistics. Results: At the end of December 2021, the International hTTP Registry had enrolled 182 confirmed hTTP patients from 49 sites in 20 countries, who were followed for a median of 3.6 (range, 0-18.5) years. The cohort included more female (n=98, 53.8%) than male (n= 84, 46.2%) patients, a gender disparity observed in adult patients because of increased diagnosis in women related to pregnancy complications. The patients were mostly White/Caucasian (n=111, 61.0%), followed by Asian (n=50, 27.5%), Black (n=2, 1.1%) and other ethnicities (n=19, 10.4%). Although 46.2% of the patients reported first symptoms of hTTP in the perinatal period (0-3 months), the median ages (ranges) at diagnosis and registry enrollment were 19.1 (0-69.9), and 30.4 (0.1-75) years, respectively. Prior to enrollment, 85.7% of patients had experienced at least one acute TTP episode with a mean (SD) of 4.3 (4.5) reported events per patient. The medical history was notable for transient ischemic attacks or strokes in 31% of hTTP patients, followed by arterial hypertension in 20%, chronic kidney disease in 12%, migraines/severe headaches in 8.2%, and seizures in 7.7%, respectively. During prospective follow-up 82 of 182 patients (45.1%) experienced 265 acute TTP episodes resulting in an overall event rate of 296.7 (95% confidence interval [CI]: 262.0-334.6) per 1000 person-years. Eight hTTP patients died during follow-up, five of them were on regular plasma prophylaxis. The causes of death were acute TTP episodes associated with cerebral (n=3; patient ages 33, 44 and 52 years) or cardiac (n=3; 39, 49, and 56 years) events, and unknown in two patients (75 and 79 years). Conclusions: The clinical burden due to recurrent acute TTP episodes and resulting neurological, cardiovascular and renal sequelae and other comorbidities is significant. Delayed diagnosis and insufficient treatment likely contributed to the observed morbidity and early mortality. Awareness, timely diagnosis and sufficient ADAMTS13 replacement therapy (for acute episodes and prophylactically) are crucial for improving short- and long-term clinical outcomes and disease burden in hTTP.

Estimating the Population-Based Prevalence of Congenital Thrombotic Thrombocytopenic Purpura Using Large-Scale Sequencing Data

Introduction Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disorder caused by severe ADAMTS13 deficiency. This severe deficiency (<10%) is classified into two forms of acquired or hereditary TTP. Acquired TTP is either due to circulating autoantibodies inhibiting ADAMTS13 activity or increasing its clearance, whereas congenital TTP results from homozygous or compound heterozygous ADAMTS13 mutations (cTTP, Upshaw-Schulman syndrome). Because of ADAMTS13 defects, an abnormal amount of ultra-large von Willebrand factor multimers is concentrated, resulting in the formation of platelet-rich microthrombi in the circulation. Given that the true prevalence of cTTP is not established, we sought to leverage the availability of exome or genome sequences of very large numbers of individuals (genome Aggregation Database, gnomAD) to estimate the worldwide and within-population prevalence of cTTP. We also aimed to examine the global mutational landscape of ADAMTS13. Methods Exome and genome sequencing data of 141,456 subjects of gnomAD were extracted and analyzed for ADAMTS13. We comprehensively reviewed literature to identify all ADAMTS13 variants that have been associated with cTTP so far. In addition, all variants reported to be associated with cTTP in HGMD and/or LOVD datasets were included. Finally, we searched for ADAMTS13 variants in ClinVar that have been classified as “pathogenic” or “likely pathogenic”. The following gnomAD variants were considered pathogenic: variants associated with cTTP in HGMD/LOVD; nonsense, frameshift, inframe deletion/insertion variants; splicing variants affecting the first/last two intronic nucleotides; splicing variants affecting the first/last eight intronic nucleotides predicted deleterious by 4 different in silico tools; missense variants predicted deleterious by 7 different in silico tools. Using the frequencies of known or predicted pathogenic variants in ADAMTS13 of the gnomAD population (n= 141,456), we estimated the prevalence of individuals homozygous or compound heterozygous for cTTP (assuming Hardy-Weinberg equilibrium). Results Following quality controls and removing variants with no clear association with cTTP, we found that 302 different ADAMTS13 variants have been so far reported to cause cTTP in the literature, HGMD and LOVD as well as ClinVar. We then collected high-quality data from gnomAD population including 141,456 subjects with different ethnicities: 12,487 Africans/African Americans, 17,720 Latinos/Admixed Americans, 5,185 Ashkenazi Jewish, 9,977 East Asians, 12,562 Finnish Europeans, 64,603 non-Finnish Europeans, 15,308 South Asians, and 3,614 persons without an assigned ethnicity. We identified a total number of 2212 variants within ADAMTS13 among 282,912 alleles analyzed in the gnomAD population. Of these, following a conservative approach, 250 different variants were pathogenic; 83 reported to be associated with cTTP and 167 predicted to be pathogenic. Among a maximum number of 282912 alleles analyzed, 2166 alleles were affected by novel or reported variants. Of which, 53% of the affected alleles were due to known pathogenic variants and the remaining 47% were due to novel predicted variants. Considering all pathogenic variants (n=250) and only those reported (n=83), we estimated an overall cTTP prevalence of 17 and 59 individuals per million people, respectively (Table 1). Considering reported variants only, the highest prevalence of cTTP was estimated in Europeans and Finnish population (30 and 26 per 10 6), followed by Latinos/Admixed Americans (14 per 10 6) and Africans/African Americans (6 per 10 6). East and South Asian ethnicities had a lower estimated prevalence of 4 and 3 per 10 6, respectively. Ashkenazi Jewish population had the lowest estimated prevalence of cTTP (0.6 per 10 6) among all populations (Table 1). Conclusion We have attempted to estimate the worldwide and within-population prevalence of cTTP using available genome/exome sequencing data of 141,456 individuals. Our results reveal that putative disease alleles and cTTP-associated variants are more prevalent than expected and the true cTTP prevalence is more than ten times higher than was reported. This finding suggests that a large number of patients might be undiagnosed. We also established the mutational burden of ADAMTS13 by identifying 167 novel variants in addition to the 302 previously reported.

Long-term follow-up of patients with congenital thrombotic thrombocytopenia purpura receiving a plasma-derived factor VIII (Koate) that contains ADAMTS13.

Hereditary thrombotic thrombocytopenia purpura (hTTP) is an ultra-rare disorder resulting from an inherited deficiency of ADAMTS13, a von Willebrand factor (VWF)-cleaving metalloprotease. The plasma-derived factor VIII/VWF Koate (FVIII/VWFKoate ) has been shown to contain ADAMTS13, allowing for its use to treat hTTP at home by the patient/caregiver. Based on prior demonstration of safe and effective use of FVIII/VWFKoate in eight patients with hTTP, we conducted a retrospective study to gather additional data regarding the use of FVIII/VWFKoate for hTTP. This was a multicentre, retrospective, noninterventional chart review of patients who had received FVIII/VWFKoate for the management of hTTP. Data collected included demographics, medical history, relevant family history, past use and tolerability of fresh frozen plasma, and details regarding FVIII/VWFKoate therapy. The cohort included 11 patients (seven males, four females) with hTTP, ranging in age at study entry from 2 to 28years. The average duration of FVIII/VWFKoate therapy was 4.8years (range, 0.5-6.5years). Among nine patients using FVIII/VWFKoate as prophylaxis, the normalized annual rate of breakthrough TTP episodes ranged from 0.2 to 1.1 episodes/year. All nine patients who received FVIII/VWFKoate prophylaxis had thrombocytopenia recorded at baseline, while eight (88.9%) did not have thrombocytopenia after using FVIII/VWFKoate . There was one AE (unspecified) attributed to FVIII/VWFKoate . These data suggest that FVIII/VWFKoate is a safe and well-tolerated source of the missing ADAMTS13 enzyme in patients with hTTP, producing a marked reduction in thrombocytopenia prevalence, low frequency of TTP episodes, and with the added benefit of self- or caregiver-administration.

Novel ADAMTS13 mutations in a patient with congenital thrombotic thrombocytopenic purpura

ABSTRACTCongenital thrombotic thrombocytopenic purpura (TTP) is a rare autosomal recessive genetic disorder caused by mutations in the ADAMTS13 gene. Approximately 200 mutations of the ADAMTS-13 gene have been identified, although only a few have been characterized through in vitro expression studies. We conducted an investigation on a male congenital TTP patient with reduced plasma levels of ADAMTS13 activity. DNA sequence analysis revealed two mutations on chromosome 9 (1.9q34.2) in the patient’s ADAMTS13 gene. One mutation was a non-synonymous mutation (exon 5: c.A530G: p.Y177C), while the other was a nonsense mutation (exon 21: c.G2651A: p.W884X). Both mutations were found to be heterozygous. The patient’s parents had no history of thrombocytopenia or neurological symptoms. DNA sequence analysis showed the patient’s father was a heterozygote for the nonsense mutation of the ADAMTS13 gene (exon 21: c.G2651A: p.W884X), while the mother was a heterozygote for the non-synonymous mutation of the ADAMTS13 gene (exon 5: c.A530G: p.Y177C). To investigate the mechanism behind ADAMTS13 deficiency in this patient, wild type (WT), ADAMTS13 p.Y177C, and ADAMTS13 p.W884X were transiently expressed in 293-6E cells. Expression studies revealed a significant reduction in enzyme activity and secretion, although the protease was detected within the cells. The 3D structures of the natural and mutated ADAMTS-13 proteins were partially reconstructed using the Phyre2 web server. The mutation that replaces the tyrosine residue at amino acid position 177 with cysteine may result in decreased steric hindrance and a looser structure. This mutation affects the binding of calcium ions and the secretion of the enzyme from intracellular to extracellular compartments.

Identification of 8 Rare Deleterious Variants in ADAMTS13 by Next-generation Sequencing in a Chinese Population with Thrombotic Thrombocytopenic Purpura.

Thrombotic thrombocytopenic purpura (TTP) is a rare and fatal disease caused by a severe deficiency in the metalloprotease ADAMTS13 and is characterized by thrombotic microangiopathy. The present study aimed to investigate the genes and variants associated with TTP in a Chinese population. Target sequencing was performed on 220 genes related to complements, coagulation factors, platelets, fibrinolytic, endothelial, inflammatory, and anticoagulation systems in 207 TTP patients and 574 controls. Subsequently, logistic regression analysis was carried out to identify the TTP-associated genes based on the counts of rare deleterious variants in the region of a certain gene. Moreover, the associations between common variants and TTP were also investigated. ADAMTS13 was the only TTP-associated gene (OR = 3.77; 95% CI: 1.82-7.81; P=3.6×10ȡ4) containing rare deleterious variants in TTP patients. Among these 8 variants, 5 novel rare variants that might contribute to TTP were identified, including rs200594025, rs782492477, c.T1928G (p.I643S), c.3336_3361del (p.Q1114Afs*20), and c.3469_3470del (p.A1158Sfs*17). No common variants associated with TTP were identified under the stringent criteria of correction for multiple testing. ADAMTS13 is the primary gene related to TTP. The genetic variants associated with the occurrence of TTP were slightly different between the Chinese and European populations.

Adamts13 Mutation Revealed By a Recurrent Ischemic Stroke in a Young Male Patient Responding to Steroid Therapy Alone: A Case Report

ADAMTS 13 deficiency can lead to recurrent cryptogenic strokes, especially among young patients. We describe the first case of recurrent stroke due to ADAMTS13 deficiency that responded to steroid therapy alone.

A-154 Cost-effectiveness of On-site Vs Send-out Measurement of ADAMTS13 Activity in the Management of Acquired Thrombotic Thrombocytopenic Purpura

Abstract Background Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy (TMA) caused by congenital or acquired severe deficiency of disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS-13), an enzyme cleaving von Willebrand factor (VWF). ADAMTS-13 deficiency leads to the accumulation of ultra-large VWF multimers, and subsequent platelet aggregation and microthrombi formation. Aside clinical symptoms, the diagnosis of TTP is based thrombocytopenia, hemolytic anemia with the presence of schistocytes, and severely reduced activity of ADAMTS-13 (<10%). As TTP is a life-threatening condition, it is of great importance to shorten the time to the treatment, and according to the French recommendations, the triplet therapy including plasma exchange (PEX), rituximab, caplacizumab, plus corticosteroids, must be administered to patients with suspected TTP until the results of ADAMTS-13 was obtained, and be pursued only in the case of deficiency. Therefore, a rapid ADAMTS-13 testing is critical for early diagnosis and optimal management of acute TTP. Methods We compared the cost-effectiveness of a strategy based on on-site measurement of ADAMTS-13 activity using a rapid fully automated chemiluminescent assay (HemosIL AcuStar ADAMTS-13) vs its centralized measurement in a reference laboratory, as it is currently the case at our institution. For that purpose, we created two scenarios based on either its local measurement with a maximum time-to-result of 16 h (assay performed during daytime, 7/7) or its centralized measurement with a median time-to-result of 4 days (range: 2–8, as demonstrated from the 2018–2021 estimates). The triplet therapy was hypothesized to be started on admission and stopped if ADAMTS-13 activity was >10%. In case of ADAMTS-13 activity <10%, an inhibitor screening would be performed at the reference laboratory, as this assay was not expected to be locally implemented. For the calculation, we considered the costs of reagent, shipping/handling of samples to the reference laboratory, laboratory staff workload, reimbursement rates, and treatments administered in patients with suspected TTP until availability of the ADAMTS-13 result. Results Based on 2018 to 2021 estimates, there was a mean of 60 prescriptions of ADAMTS-13 activity per year. Most were for the follow-up of TTP patients and for patients with non-TTP TMA. Only seven were for the diagnosis of acute TTP, as suggested by the French score, which was confirmed in four cases (mean values). The local measurement of ADAMTS-13 activity was found to be cost-effective with a 16%-reduction of the costs compared to its centralized measurement in those seven patients with suspected TTP during the first 4 days. Conclusion Together with its short turnaround time (33 min) and its full automation, our results suggest that the HemosIL AcuStar ADAMTS-13 activity assay could be an assay of choice to rapidly measure ADAMTS-13 activity in the plasma and thus to establish the diagnosis of acute TTP in emergency settings. Considering the local costs, using the strategy based on the local evaluation of ADAMTS-13 activity led to a 16%-reduction of the overall costs during the first 4 days after admission of the seven patients with suspected acute TTP.

A Global Assessment of Coagulation Profile and a Novel Insight into Adamts-13 Implication in Neonatal Sepsis.

Neonatal sepsis is a life-threatening condition associated with significant morbidity and mortality. Sepsis-induced coagulopathy is a well-recognized entity, signifying the strong cross-talk between inflammation and coagulation. The aim of the present study was to compare the coagulation profile between the acute phase of sepsis and recovery in term and preterm neonates. Additional comparisons to healthy neonates were undertaken. Levels of clotting, anti-clotting factors and ADAMTS-13 (A disintegrin and metalloprotease with thrombospondin type-1 motives), the cleaving protein of von Willebrand factor (VWF), were measured in 16 term and preterm neonates in the acute phase of infection and following recovery, as well as in 18 healthy neonates. Clotting times were prolonged, while levels of particular clotting factors were lower in the acute phase of infection compared to controls and recovery. On the other hand, levels of fibrinogen, factor VIII (FVIII) and VWF were significantly higher in the acute phase in comparison to controls and recovery, while they remained persistently higher in the infection group compared to controls. In regard to the anticlotting mechanism, a clear suppression was observed in septic neonates. ADAMTS-13 levels were significantly lower in the acute phase of infection in comparison to controls and recovery (p = 0.015 and 0.004, respectively), while a trend toward superimposed normalization was demonstrated post infection, as higher ADAMTS-13 levels were measured in recovered neonates compared to controls (p = 0.002). The coagulation profile is considerably deranged in neonatal sepsis. ADAMTS-13 deficiency in septic neonates is a novel finding with promising future implications, as ADAMTS-13 substitution may serve as a useful therapeutic option in neonatal sepsis, prompting further investigation in future studies.

Anti-ADAMTS13 Autoantibodies: From Pathophysiology to Prognostic Impact-A Review for Clinicians.

Thrombotic thrombocytopenic purpura (TTP) is a fatal disease in which platelet-rich microthrombi cause end-organ ischemia and damage. TTP is caused by markedly reduced ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity. ADAMTS13 autoantibodies (autoAbs) are the major cause of immune TTP (iTTP), determining ADAMTS13 deficiency. The pathophysiology of such autoAbs as well as their prognostic role are continuous objects of scientific studies in iTTP fields. This review aims to provide clinicians with the basic information and updates on autoAbs' structure and function, how they are typically detected in the laboratory and their prognostic implications. This information could be useful in clinical practice and contribute to future research implementations on this specific topic.

Recombinant ADAMTS-13 Improves Survival of Mice Subjected to Endotoxemia.

When stimulated by proinflammatory mediators, endothelial cells release ultra-large von Willebrand factor (ULVWF) multimers that are hyperactive in activating and aggregating platelets. These ULVWF multimers can accumulate in the circulation and on the inflamed endothelium because they are insufficiently cleaved by the metalloprotease ADAMTS-13, which becomes moderately deficient under conditions of systemic inflammation. This moderate ADAMTS-13 deficiency may lead to thrombotic complications that contribute to ischemic tissue injury and organ failure that are associated with severe infections. To test this hypothesis, we investigated whether recombinant ADAMTS-13 improves the pathological course of endotoxemia in lipopolysaccharide (LPS)-treated mice. C57BL/J6 mice received a bolus infusion of either 5 µg/mouse of ADAMTS-13 or vehicle control 30 min after LPS challenge and were monitored for seven-day survival. During the monitoring period, platelet counts, VWF antigen, and ADAMTS-13 activity were measured. Thrombosis was also examined by the immunohistochemistry in the liver. We found that ADAMTS-13 reduced mortality from 66% to 34.9%. The improved survival was associated with a greater recovery from thrombocytopenia, higher plasma ADAMTS-13 activity, and less thrombotic vascular occlusion. These results suggest that systemic inflammation could result in deficient ULVWF proteolysis by ADAMTS-13 and that ADAMTS-13 improves the outcomes of endotoxemia-induced inflammation.

#3479 RISK FACTORS OF DEATH OR CHRONIC RENAL REPLACEMENT THERAPY REQUIREMENTS IN PATIENTS WITH THROMBOTIC MICROANGIOPATHIES WITHOUT ADAMTS-13 DEFICIENCY

Abstract Background and Aims Thrombotic microangiopathy without severe ADAMTS-13 deficiency activity levels (TMA-13n) has a high mortality rate. Early recognition of patients at higher risk of dying or needing chronic renal replacement therapy (composite outcome: CO) has become of paramount importance since treatments such as eculizumab could ameliorate the prognosis of this group of patients. Plasmic score have been shown to predict severe ADAMTS-13 deficiency; however, its role as a prognostic factor of CO in TMA-13n is unknown. Method We retrospectively evaluate the potential factors associated with the risk of CO. Patients diagnosed with TMA-13n (defined by microangiopathic anaemia, thrombocytopenia, organ damage and ADAMTS-13 activity ≥ 10%) from January 2008 to May 2018 in our centre were included in the study. Results Forty-two consecutive patients were included. Mean (SD) age: 41(20) years. Twenty-five (60% were females. Mean (SD) ADAMTS-13 activity: 69 (24%). Twenty-six (62%) patients required dialysis at admission. Nineteen (45%) met CO (10 patients died). Higher age, lower lactate dehydrogenase, PLASMIC score values ≤ 4, neuroradiological damage and early eculizumab use [median (IQR): 4 (0-16) days from hospital admission: 5] were factors associated with the risk for developing CO. Only three factors were independently associated with CO mortality by logistic regression: early use of eculizumab (OR: 0.14; 95% CI: 0.02-0.94) and neuroradiological damage (OR: 6.67; 95% CI: 1.12-39.80) and PLASMIC score ≤ 4 (OR: 7.39; 95% CI: 1.18-46.11). Conclusion In TMA-13n patients, neuroradiological damage, low PLASMIC score and early use of eculizumab were independent prognostic factors of death and chronic renal replacement therapy requirements.

Health following recovery from immune thrombotic thrombocytopenic purpura: the patient's perspective.

The impact of residual symptoms following recovery from immune-mediated thrombotic thrombocytopenic purpura (iTTP) on activities of daily living during remission is not routinely discussed or evaluated by hematologists. This study used qualitative methodology to understand 3 issues from the patient's perspective: the most important symptoms during remission, the impact of these symptoms on their daily activities, and the effectiveness of communication with hematologists. Oklahoma and Ohio patients participated in either focus groups or individual interviews. Eligibility included age ≥18 years, ADAMTS13 deficiency (<10% activity) at diagnosis or relapse, and in clinical remission (≥1 year from episode). A nonprobabilistic purposive sampling approach was used. The most important symptoms were defined as symptoms mentioned across all 7 focus groups. The interviews supplemented focus group data. The analysis focused on describing the impact of symptoms and barriers to communicating with hematologists. A total of 44 patients participated (focus groups, N= 25; interviews, N= 19). The most important symptoms affecting the patients' daily activities were cognitive issues, anxiety, depression, and fatigue. These symptoms affected patients' ability to return to their previous level of functioning and created difficulties in relationships. A key communication barrier with their hematologists was forgetting to mention these symptoms. Although hematologists pronounce patients as recovered, iTTP remains a life-changing event. Patients often did not return to their previous functioning; relationships and careers were affected. However, patients may forget to discuss these concerns with their hematologist. To improve remission care, hematologists should incorporate patient-reported outcome measures evaluating these symptoms in remission visits.

Immune and Hereditary Thrombotic Thrombocytopenic Purpura: Can ADAMTS13 Deficiency Alone Explain the Different Clinical Phenotypes?

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by a hereditary or immune-mediated deficiency of the enzyme ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). TTPs are caused by the following pathophysiological mechanisms: (1) the presence of inhibitory autoantibodies against ADAMTS13; and (2) hereditary mutations of the ADAMTS13 gene, which is present on chromosome 9. In both syndromes, TTP results from a severe deficiency of ADAMTS13, which is responsible for the impaired proteolytic processing of high-molecular-weight von Willebrand factor (HMW-VWF) multimers, which avidly interact with platelets and subendothelial collagen and promote tissue and multiorgan ischemia. Although the acute presentation of the occurring symptoms in acquired and hereditary TTPs is similar (microangiopathic hemolytic anemia, thrombocytopenia, and variable ischemic end-organ injury), their intensity, incidence, and precipitating factors are different, although, in both forms, a severe ADAMTS13 deficiency characterizes their physiopathology. This review is aimed at exploring the possible factors responsible for the different clinical and pathological features occurring in hereditary and immune-mediated TTPs.

The Specificities of Thrombotic Thrombocytopenic Purpura at Extreme Ages: A Narrative Review.

Thrombotic thrombocytopenic purpura (TTP) is a rare and life-threatening thrombotic microangiopathy (TMA) related to a severe ADAMTS13 deficiency, the specific von Willebrand factor (VWF)-cleaving protease. This deficiency is often immune-mediated (iTTP) and related to the presence of anti-ADAMTS13 autoantibodies that enhance its clearance or inhibit its VWF processing activity. iTTP management may be challenging at extreme ages of life. International cohorts of people with TTP report delayed diagnoses and misdiagnoses in children and elderly people. Child-onset iTTP shares many features with adult-onset iTTP: a female predominance, an idiopathic presentation, and the presence of neurological disorders and therapeutic strategies. Long-term follow-ups and a transition from childhood to adulthood are crucial to preventing iTTP relapses, in order to identify the occurrence of other autoimmune disorders and psychosocial sequelae. In contrast, older iTTP patients have an atypical clinical presentation, with delirium, an atypical neurological presentation, and severe renal and cardiac damages. They also have a poorer response to treatment and prognosis. Long-term sequelae are highly prevalent in older patients. Prediction scores for iTTP diagnoses are not used for children and have a lower sensitivity and specificity in patients over 60 years old. ADAMTS13 remains the unique biological marker that is able to definitely confirm or rule out the diagnosis of iTTP and predict relapses during follow-ups.

Use of n-acetylcysteine therapy in patients with relapsed refractory thrombotic thrombocytopenic purpura

There is limited data on the use of NAC in the literature. We would like to present the satisfactory results we obtained in our resistant and relapsed patients as a case series.Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy caused by ADAMTS13 (a disintegrin with thrombospondin type 1 motif and metalloprotease activity, member13) deficiency. Von Willebrand factor (vWF) initiates platelet aggregation and thus thrombus formation. The multimers of vWF are cleaved by ADAMTS13. Because of the decreased activity of ADAMTS13, ultra-large multimers accumulate and end-organ damage occurs. TTP is characterized by microangiopathic hemolytic anemia (MAHA), severe thrombocytopenia, and organ ischemia resulting from vascular occlusion caused by thrombi. Plasma exchange therapy (PEX) remains the mainstay of TTP therapy. Patients who do not respond to PEX and corticosteroids require additional treatments such as rituximab and caplacizumab. NAC reduces disulfide bonds in mucin polymers through its free sulfhydryl group. Thus, the size and viscosity of the mucins are reduced. VWF is structurally similar to mucin. Based on this similarity, Chen and colleagues showed that NAC can reduce the size and reactivity of ultralarge multimers of vWF, such as ADAMTS13. Currently, there is not much information to suggest that NAC has any clinical value in the treatment of TTP. In this case series of 4 refractory patients, we would like to present the responses we obtained with the addition of NAC therapy. NAC can be added to PEX and glucocorticoid therapy as supportive therapy, especially in unresponsive patients.

Performance Validation of Three Scoring Systems for the Prediction of Thrombotic Microangiopathy Due to Severe ADAMTS13 Deficiency and the Response to Therapeutic Plasma Exchange: First Study in Korea.

The BENTLEY score (B-S), French thrombotic microangiopathy (TMA) Reference Center score (FTMA-S), and PLASMIC score (PLASMIC-S) have been developed for TMA diagnostic prediction. We retrospectively validated their predictive performances in patients with severe (<10%) disintegrin and metalloprotease with thrombospondin type 1 motif, member 13 (ADAMTS13) deficiency in terms of the risk of TMA and response to therapeutic plasma exchange (TPE). The predictive performances of the three scoring systems were compared in 145 patients with suspected TMA who underwent ADAMTS13 activity tests between January 2014 and September 2022. The response to TPE and mortality in TMA-positive patients were compared after risk stratification, using the Mann-Whitney U and Fisher's exact tests. The PLASMIC-S, FTMA-S, and B-S showed area under the curve values of 0.820, 0.636, and 0.513, respectively, for predicting TMA positivity in high-risk patients. The PLASMIC-S showed higher sensitivity (81.8%), negative predictive value (91.2%), positive predictive value (PPV; 66.7%), and accuracy (82.1%) than the FTMA-S (72.7%, 82.1%, 41.0%, and 60.0%, respectively) and B-S (4.6%, 70.2%, 50.0%, and 69.7%, respectively). The PLASMIC-S also showed higher specificity than the FTMA-S (82.2% vs. 54.5%). The modified PLASMIC-S, including lactate dehydrogenase/upper limit of normal ratios, increased the specificity, PPV, and accuracy to 97.0%, 92.3%, and 92.4%, respectively. In TMA-positive patients, high risk assessed by the PLASMIC-S predicted higher platelet recovery rates and less TPE sessions required for recovery than for those assessed at low-to-intermediate risk. PLASMIC-S is the preferred scoring system for detecting patients with TMA positivity and for prognosis before confirmation of ADAMTS13 activity.

5599228 PITFALLS IN DIAGNOSING THROMBOTIC THROMBOCYTOPENIC PURPURA IN SICKLE CELL DISEASE

Background: Thrombotic microangiopathies are diagnosed by thrombocytopenia, microangiopathic haemolytic anaemia and evidence of end organ damage. In TTP this includes neurological symptoms, renal impairment and cardiac microthrombi. Confirmation of the diagnosis is severe deficiency (<10%) of the metalloproteinase ADAMTS13 and/or the presence of an inhibitor. The diagnosis of TTP in sickle cell disease (SCD) can be challenging as SCD is characterised by a chronic state of haemolysis often with very abnormal peripheral blood morphology so clinical features suggestive of TTP can be due to complications of SCD. More specifically, the coexistence of neurological impairment and thrombocytopenia seen in fat embolism syndrome (FES) complicating SCD can lead to an erroneous diagnosis of TTP. FES typically affects non-homozygous patients and those with a previously mild course of their illness manifesting with respiratory failure, neurological signs, thrombocytopenia and potential involvement of any system leading to high morbidity and mortality. Peripheral blood morphology typically shows very high number of nucleated red blood cells (nRBC). Aims: To identify published cases of TTP in patients with SCD and review the diagnostic approach. Methods: A PubMed literature search was performed using the terms “sickle cell” and “thrombotic thrombocytopenic purpura”/”TTP”. Results: Of 19 cases identified, 9 were individual case reports and a case series of 10. All patients had very mild course of their SCD. The median nadir platelet count was 38 x 109/L (7-70). 84% had neurological involvement either at presentation or shortly afterwards; primarily altered sensorium/drop in GCS. 79% patients also had severe type I respiratory failure either preceding or occurring simultaneously with the development of neurological signs and associated with extensive changes on chest imaging. Schistocytes were identified in all cases but in the vast majority at relatively low levels; at the same time, all showed large numbers of nRBCs. 18 of the 19 cases were published after 1998; in 15 there was no mention of ADAMTS13 testing at all. In the 3 cases with ADAMTS13 levels, all were normal; 2 samples were obtained before therapeutic plasma exchange (TPE) and 1 after. 18 patients received TPE and 1 an infusion of donor plasma. However, prior to TPE, all patients had already received red cell transfusion achieving Hb S levels of 30% or less. There were 2 (11%) deaths while the remainder of patients achieved complete recovery. One due to intracranial haemorrhage and the other, sepsis in the context of immunosuppression for prevention of TTP recurrence. The presence of early respiratory failure, the inconclusive morphological findings, the degree of thrombocytopenia, and the complete absence of confirmatory ADAMTS13 results bring the diagnosis of TTP to question in all cases. Given the clinical presentations, we suspect that some of these patients had FES. The positive outcomes may be explained by the fact that all patients received adequate red cell transfusion, but also the possible beneficial effect of TPE in acute complications of SCD with a hyper inflammatory component such as FES. Conclusion: The diagnosis of TTP in patients with SCD is challenging due to many overlapping features. It should not be made without confirmatory ADAMTS13 results and the possibility of alternative diagnoses should be explored.