ADAMTS13 in the New Era of TTP.

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening, often immune-mediated disease that affects 2-13 persons per million per year. Hemolytic anemia, thrombocytopenia, and end-organ damage due to the formation of microthrombi are characteristic of TTP. ADAMTS13 is a disintegrin, metalloproteinase, cleaving protein of von Willebrand factor (VWF) that processes the VWF multimers to prevent them from interacting with platelets and, in turn, to microvascular thrombosis. Prompt diagnosis of TTP is critical yet challenging. Thrombotic microangiopathies have similar clinical presentation. Measurement of ADAMTS13 activity helps in the differential diagnosis. Less than 10% ADAMTS13 activity is indicative of TTP. Laboratory ADAMTS13 activity assays include incubating the test plasma with the substrate (full-length VWM multimers) and detection with direct or indirect measurement of the cleavage product. The purpose of this study is to examine the diagnostic potential, advantages, and weaknesses of the ADAMTS13 potency in TTP.

Identification of HLA alleles involved in immune thrombotic thrombocytopenic purpura patients from Turkey.

Thrombotic thrombocytopenic purpura (TTP) is one of the rare group disorders classified as thrombotic microangiopathies (TMAs). Approximately 90% of TTP developed immune-mediation by the formation of antibodies against the enzyme ADAMTS-13. The exact cause is unknown. To establish an association between human leukocyte antigen (HLA) and autoimmune basis, as susceptibility or protection against the disease, we contributed a study aiming to evaluate the role of HLA in immune-mediated TTP (iTTP). Considering epidemiological factors such as age, sex, ethnicity, and geographical origins, we contributed the study in our country, Turkey, which consist of a very heterogeneous population. Patients' data collection was retrospectively from electronic database on two University hospitals having big therapeutic apheresis service. Control arm was healthy people registered as stem cell donors matched in terms of age and sex. The frequency of HLA-DRB1 and HLA-DQB1 alleles between acquired TTP and the control group was compared using the chi-square method. Yates correction and logistic regression were performed on these results. A total of 75 iTTP patients and 150 healthy individuals enrolled to the study. HLA-DRB1∗11, HLA-DQB1∗03, HLA-DRB1∗11:01, HLA-DRB1∗14:01, HLA-DRB1∗13:05, HLA-DRB1∗11 + HLA-DQB1∗03 allele pair and HLA-DRB1∗15 + HLA- DQB1∗06 were proved to be susceptibility allele pairs for iTTP. HLA-DRB1∗15, HLA-DRB1∗01:01, HLA-DRB1∗07:01, HLA-DRB1∗13:01, HLA-DRB1∗14:54, HLA-DQB1∗05:01, HLA-DQB1∗02:02 and HLA-DRB1∗07 + HLA-DQB1∗02 allele pair were found to be protective against iTTP. Our findings support an association with iTTP across very heterogenous populations in Turkey.

[Advances in the treatment of thrombotic thrombocytopenic purpura].

Thrombotic thrombocytopenic purpura (TTP) is a fatal thrombotic disease caused by a marked decrease in the activity of ADAMTS13, a von Willebrand factor cleaving protease. In congenital TTP, ADAMTS13 activity is decreased by an abnormality in ADAMTS13, and in acquired TTP, by anti-ADAMTS13 autoantibody. Death from thrombosis in the acute phase has been an issue with conventional treatment of acquired TTP by plasma exchange or immunosuppressive therapy. However, the advent of caplacizumab, an anti-VWF nanobody, has made it possible to suppress thrombus formation and is expected to improve survival rates. In addition, some case series have shown the efficacy of caplacizumab without plasma exchange for acquired TTP, and this approach is being investigated in clinical trials. Fresh-frozen plasma is transfused to supply ADAMTS13 for congenital TTP, but frequent transfusions over a long period of time can lead to problems such as infection and allergic reactions. Novel therapies such as recombinant ADAMTS13 products and gene therapy are now under development, and show promise for future clinical use.

Global prevalence of hereditary thrombotic thrombocytopenic purpura determined by genetic analysis.

ABSTRACT: Hereditary thrombotic thrombocytopenic purpura (hTTP) is a rare autosomal recessive, life-threatening disorder caused by a severe deficiency of the plasma enzyme, ADAMTS13. The current estimated prevalence of hTTP in different regions of the world, 0.5 to 2.0 patients per million, is determined by the frequency of diagnosed patients. To evaluate more accurately the worldwide prevalence of hTTP, and also the prevalence within distinct ethnic groups, we used data available in exome and genome sequencing of 807 162 (730 947 exomes, 76 215 genomes) subjects reported recently by the Genome Aggregation Database (gnomAD-v4.1). Among 1 614 324 analyzed alleles in the gnomAD population we identified 6321 distinct ADAMTS13 variants. Of these, 758 were defined as pathogenic; 140 (18%) variants had been previously reported and 618 (82%) were novel (predicted as pathogenic). In total 10 154 alleles (0.6%) were carrying the reported or predicted pathogenic variants; 7759 (77%) with previously reported variants. Considering all 758 pathogenic variants and also only the 140 previously reported variants, we estimated a global hTTP prevalence of 40 and 23 cases per 106, respectively. Considering only the 140 previously reported variants, the highest estimated prevalence was in East Asians (42 per 106). The estimated prevalences of other populations were: Finnish, 32 per 106; non-Finnish Europeans, 28 per 106; Admixed Americans, 19 per 106; Africans/African Americans, 6 per 106; and South Asians, 4 per 106. The lowest prevalences were Middle Eastern, 1 per 106 and Ashkenazi Jews, 0.7 per 106. This population-based genetic epidemiology study reports that hTTP prevalence is substantially higher than the currently estimated prevalence based on diagnosed patients. Many patients with hTTP may not be diagnosed or may have died during the neonatal period.

Atypical Presentations of Pediatric-acquired Thrombotic Thrombocytopenic Purpura.

BACKGROUND: Immune thrombotic thrombocytopenic purpura (iTTP) in children is a rare, severe thrombotic microangiopathy. This condition is characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and organ ischemia due to reduced activity of the von Willebrand factor-cleaving protease ADAMTS13. METHODS: A retrospective case series evaluating data collected from the medical files of 4 children diagnosed with iTTP. RESULTS: The presented case series depicts a variety of iTTP presentations: 1 case of primary iTTP, 1 case induced by Shiga toxin, 1 associated with RAS-associated autoimmune leukoproliferative disease (RALD), and 1 initial manifestation of systemic lupus erythematosus (SLE). Notably, 2 patients recovered without undergoing plasma exchange. CONCLUSION: Early ADAMTS13 testing in children with unexplained hemolysis or thrombocytopenia is crucial. The diverse underlying causes, including infections and autoimmune disorders, underscore the complexity of iTTP in the pediatric population. These cases highlight the necessity for personalized treatment approaches that consider each patient's unique clinical situation and potential alternatives or modifications to conventional therapeutic regimens.

Efficacy and relative safety of caplacizumab in immune-mediated thrombotic thrombocytopenic purpura: a systematic review and meta-analysis.

Immune-mediated thrombotic thrombocytopenia purpura (iTTP) is a rare microvascular disease characterized by severe disseminated microvascular thrombose-bleeding syndrome. Caplacizumab has been approved for the treatment of iTTP in combination with Plasma Exchange (PE) and immunosuppressive therapy, but its role in iTTP therapy remains uncertain. Therefore, we conducted a meta-analysis to investigate the safety and efficacy of caplacizumab for the treatment of patients with iTTP. We searched electronic databases (PubMed, Embase, Cochrane Library, and Scopus) and reference lists of relevant articles to find articles published from 2015 to 2022. The time to normalization of the platelet count of the group caplacizumab is shorter than the group placebo (SMD = -0.72; 95% CI -0.88 to -0.56; P  < 0.05). Caplacizumab reduced the incidence of mortality (OR = 0.41; 95% CI 0.18-0.92; P  < 0.05), exacerbations (OR = 0.10; 95% CI 0.05-0.18; P  < 0.05), and recurrence (OR = 0.17; 95% CI 0.06-0.50; P  < 0.05). However, the bleeding events in the caplacizumab group were higher than those in the placebo group, especially severe bleeding events. There was no difference in ADAMTS13 activity and thromboembolic events between the two groups. Our analysis indicated that caplacizumab is effective and well tolerated for the treatment of iTTP. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42022362370.

Detection of novel duplication variant in ADAMTS13 gene using chromosomal microarray analysis.

We present a case of a child with congenital thrombotic thrombocytopenic purpura found to have a compound heterozygous variant in the ADAMTS13 gene with a novel variant resulting in a large duplication of exons 9-11 of ADAMTS13 This variant was identified through additional molecular testing via a chromosomal microarray analysis. To our knowledge, this assay had not previously been utilised to identify an ADAMTS13 variant and the additional testing was possible through the involvement of a genetic counsellor.

Plasma exchange in thrombotic thrombocytopenic purpuras.

INTRODUCTION: Thrombotic thrombocytopenic purpura (TTP) is a rare but potentially fatal hematological disorder that requires urgent treatment. Once the diagnosis has been made, plasma exchange (PE) must be started immediately and until a response is obtained. AIM: Evaluate PE in terms of responses and complications in the treatment of TTP. METHODS: This was a monocentric, descriptive, retrospective study including patients in whom TTP was diagnosed and treated with plasmapheresis in the clinical hematology department at Aziza Othmana Hospital, between January 2010 and December 2020. RESULTS: Our study included 26 patients. PE was initiated within a median of 1 day. The rhythm of exchanges was daily in 22 patients. Twenty PE-related complications were noted, hypocalcemia being the most frequent (30%). CR was achieved in 15 patients after PE alone. Nine patients were refractory, and six received 2nd-line treatment, with CR achieved in five patients. Relapse was noted in six patients (40%). They were treated by PE and only one patient received rituximab. Four patients had a response. The overall response rate was 69% and overall mortality was 30%. OS at 2 years was 68,3% and RFS was 84,4%. Factors associated with the achievement of CR were the fall in LDH at D5 of treatment (p=0,027,OR=0,59 ;IC 95%[0,32-1,08]) and the daily rhythm of PE (p=0,005, OR=0,35; IC 95%[0,14-0,91]). CONCLUSION: Our results were comparable to those of the literature, but the rate of refractory disease was higher. Rituximab may enhance our results.

The use of 1E12, a monoclonal anti-platelet factor 4 antibody, to improve the diagnosis of vaccine-induced immune thrombotic thrombocytopenia.

BACKGROUND: Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a complication of adenoviral-based vaccine against SARS-CoV-2 due to prothrombotic immunoglobulin (Ig) G antibodies to platelet factor 4 (PF4) and may be difficult to distinguish from heparin-induced thrombocytopenia (HIT) in patients treated with heparin. OBJECTIVES: We assessed the usefulness of competitive anti-PF4 enzyme immunoassays (EIAs) in this context. METHODS: The ability of F(ab')2 fragments of 1E12, 1C12, and 2E1, 3 monoclonal anti-PF4 antibodies, to inhibit the binding of human VITT or HIT antibodies to PF4 was evaluated using EIAs. Alanine-scanning mutagenesis was performed to define the amino acids involved in the interactions between the monoclonal antibodies and PF4. RESULTS: A strong inhibition of VITT IgG binding to PF4 was measured with 1E12 (median inhibition, 93%; n = 8), whereas it had no effect on the binding of HIT antibodies (median, 6%; n = 8). In contrast, 1C12 and 2E1 inhibited VITT (median, 74% and 76%, respectively) and HIT antibodies (median, 68% and 53%, respectively) binding to PF4. When a competitive anti-PF4 EIA was performed with 1E12 for 19 additional VITT samples, it strongly inhibited IgG binding to PF4, except for 1 patient, who had actually developed HIT according to the clinical history. Epitope mapping showed that 1E12 interacts with 5 key amino acids on PF4, of which 4 are also required for the binding of human VITT antibodies, thus explaining the competitive inhibition. CONCLUSION: A simple competitive anti-PF4 EIA with 1E12 could help confirm VITT diagnosis and distinguish it from HIT in patients when both diagnoses are possible.

Novel mechanisms of action of emerging therapies of hereditary thrombotic thrombocytopenic purpura.

INTRODUCTION: Hereditary thrombotic thrombocytopenic purpura (hTTP) is caused by deficiency of plasma ADAMTS13 activity, resulting from ADAMTS13 mutations. ADAMTS13 cleaves ultra large von Willebrand factor (VWF), thus reducing its multimer sizes. Hereditary deficiency of plasma ADAMTS13 activity leads to the formation of excessive platelet-VWF aggregates in small arterioles and capillaries, resulting in hTTP. AREAS COVERED: PubMed search from 1956 to 2024 using thrombotic thrombocytopenic purpura and therapy identified 3,675 articles. Only the articles relevant to the topic were selected for discussion, which focuses on pathophysiology, clinical presentations, and mechanisms of action of emerging therapeutics for hTTP. Current therapies include infusion of plasma, or coagulation factor VIII, or recombinant ADAMTS13. Emerging therapies include anti-VWF A1 aptamers or nanobody and gene therapies with adeno-associated viral vector or self-inactivated lentiviral vector or a sleeping beauty transposon system for a long-term expression of a functional ADAMTS13 enzyme. EXPERT OPINION: Frequent plasma infusion remains to be the standard of care in most parts of the world, while recombinant ADAMTS13 has become the treatment of choice for hTTP in some of the Western countries. The success of gene therapies in preclinical models may hold a promise for future development of these novel approaches for a cure of hTTP.

Hydroxychloroquine-Induced Nonthrombocytopenic Purpura: A Case Series.

Hydroxychloroquine (HCQ) is a disease-modifying anti-rheumatic medication for the treatment of various autoimmune conditions. A rare side effect of HCQ is thrombotic thrombocytopenic purpura (TTP). We present two cases of patients who developed purpura that did not meet TTP criteria following treatment with HCQ. While the etiology of HCQ-associated TTP is poorly understood, we propose a spectrum of manifestations related to HCQ, ranging from benign purpura to TTP. As multiple factors contribute to the disease, we believe that HCQ may act as a "second hit" in patients with genetic susceptibility, which also influences the variability in the severity of disease manifestations. J Drugs Dermatol. 2024;23(5):e124.     doi:10.36849/JDD.7781e.

Plasmapheresis combined with rituximab treatment of a case of thrombotic thrombocytopenic purpura with Sjögren syndrome and renal impairment: A case report.

RATIONALE: Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy caused by reduced activity of the von Willebrand factor-cleaving protease (ADAMTS13), which can be life-threatening. The patient reported in this case study also had concurrent Sjögren syndrome and renal impairment, presenting multiple symptoms and posing a great challenge in treatment. PATIENT CONCERNS: A 25-year-old woman in the postpartum period visited the hospital due to indifference in consciousness for more than 1 day following cesarean section 8 days prior. DIAGNOSIS: Notable decreases were observed in platelets, hemoglobin, creatinine, and ADAMTS13 levels. After a consultative examination by an ophthalmologist, she was diagnosed with retinal hemorrhage in the right eye and dry eye syndrome in both eyes. INTERVENTIONS: Having been diagnosed with TTP with Sjögren syndrome and renal impairment, she received repeated treatments with plasmapheresis combined with rituximab. OUTCOMES: Following treatment and during the follow-up period, the patient's platelet counts and bleeding symptoms significantly improved. LESSONS: TTP has a high mortality rate, and when combined with Sjögren syndrome and renal impairment, it poses an even greater challenge in treatment. However, after administering standard plasmapheresis combined with rituximab treatment, the treatment outcome is favorable.