Factor XI deficiency in Ashkenazi Jews in Israel

Will Factor XI Inhibitors Replace Current Anticoagulants for Stroke Prevention in Atrial Fibrillation?

PURPOSE OF REVIEW

This review provides an overview of the factor XI (FXI) inhibitor hypothesis for the development of novel anticoagulants which may be safer to those currently used in clinical practice and describes preliminary clinical data from phase 2 dose-ranging studies of patients with atrial fibrillation.

RECENT FINDINGS

Recent data from phase 2 dose ranging studies demonstrate substantial reductions in bleeding with FXI pathway inhibition compared with currently approved anticoagulants. However, larger studies are necessary to demonstrate efficacy of FXI inhibition for stroke prevention in atrial fibrillation. FXI pathway inhibition holds great promise for revolutionizing the landscape of anticoagulation for atrial fibrillation, primarily by reducing bleeding risk; however, further data are necessary to demonstrate efficacy.

Asundexian versus Apixaban in Patients with Atrial Fibrillation

BACKGROUND

Stroke prevention with direct-acting oral anticoagulant agents in patients with atrial fibrillation confers a risk of bleeding and limits their use. Asundexian, an activated factor XI (XIa) inhibitor, is an oral anticoagulant that may prevent strokes with less bleeding.

METHODS

In a phase 3, international, double-blind trial, we randomly assigned high-risk patients with atrial fibrillation in a 1:1 ratio to receive asundexian at a dose of 50 mg once daily or standard-dose apixaban. The primary efficacy objective was to determine whether asundexian is at least noninferior to apixaban for the prevention of stroke or systemic embolism. The primary safety objective was to determine whether asundexian is superior to apixaban with respect to major bleeding events.

RESULTS

A total of 14,810 randomly assigned patients were included in the intention-to-treat population. The mean (±SD) age of the patients was 73.9±7.7 years, 35.2% were women, 18.6% had chronic kidney disease, 18.2% had a previous stroke or transient ischemic attack, 16.8% had received oral anticoagulants for no more than 6 weeks, and the mean CHA2DS2-VASc score (range, 0 to 9, with higher scores indicating a greater risk of stroke) was 4.3±1.3. The trial was stopped prematurely at the recommendation of the independent data monitoring committee. Stroke or systemic embolism occurred in 98 patients (1.3%) assigned to receive asundexian and in 26 (0.4%) assigned to receive apixaban (hazard ratio, 3.79; 95% confidence interval [CI], 2.46 to 5.83). Major bleeding occurred in 17 patients (0.2%) who received asundexian and in 53 (0.7%) who received apixaban (hazard ratio, 0.32; 95% CI, 0.18 to 0.55). The incidence of any adverse event appeared to be similar in the two groups.

CONCLUSIONS

Among patients with atrial fibrillation at risk for stroke, treatment with asundexian at a dose of 50 mg once daily was associated with a higher incidence of stroke or systemic embolism than treatment with apixaban in the period before the trial was stopped prematurely. There were fewer major bleeding events with asundexian than with apixaban during this time. (Funded by Bayer; OCEANIC-AF ClinicalTrials.gov number, NCT05643573; EudraCT number, 2022-000758-28.).

Factor XIa inhibition as a therapeutic strategy for atherothrombosis

When selecting an anticoagulant, clinicians consider individual patient characteristic, the treatment indication, drug pharmacology, and safety and efficacy as demonstrated in randomized trials. An ideal anticoagulant prevents thrombosis with little or no increase in bleeding. Direct oral anticoagulants represent a major advance over traditional anticoagulants (e.g., unfractionated heparin, warfarin) but still cause bleeding, particularly from the gastrointestinal tract which can limit their use. Epidemiological studies indicate that patients with congenital factor XI (FXI) deficiency have a lower risk of venous thromboembolism (VTE) and ischemic stroke (IS) than non-deficient individuals, and do not have an increased risk of spontaneous bleeding, even with severe deficiency. These observations provide the rationale for targeting FXI as a new class of anticoagulant. Multiple FXI inhibitors have been introduced and several are being evaluated in Phase III trials. In this review, we explain why drugs that target FXI may be associated with a lower risk of bleeding than currently available anticoagulants and summarize the completed and ongoing trials.

Diagnosis and management of factor XI alloinhibitors in patients with congenital factor XI deficiency-A large single-centre experience

INTRODUCTION

Factor (F) XI deficiency is an inherited bleeding disorder with increased prevalence in Ashkenazi Jews where it is mainly caused by two variants, p.Glu135* (type II, leading to a null allele) and p.Phe301Leu (type III, missense variant). Inhibitor development is rare, and only seen in severe FXI deficiency (<20 IU/dL) upon exposure to plasma-based products. We report our experience of a large cohort of patients with severe FXI deficiency, including seven patients who developed FXI alloinhibitors, their presentation, natural history and subsequent perioperative management.

METHODS

A single-centre retrospective database review of patients with FXI deficiency, including those who have subsequently developed inhibitors, and extraction of clinical, laboratory and genotype data, including operative management records.

RESULTS

A total of 682 patients were identified with FXI deficiency, of whom 113 had FXI < 20 IU/dL and 42 had FXI ≤ 1 IU/dL. Factor XI inhibitors were seen in seven patients, six of whom were homozygous for the type II variant (prevalence of inhibitor with this genotype of 30%, risk of inhibitor upon plasma exposure 50%). FXI inhibitors were not seen, despite similar exposures, in patients with other genotypes. No alteration in bleeding phenotype occurred after inhibitor development and subsequent surgery was managed on 13 occasions with recombinant factor VIIa (rFVIIa), including low doses (15-30 µg/kg), with good haemostasis. The inhibitor spontaneously disappeared in four of seven patients over 1-22 years.

CONCLUSION

FXI inhibitors were only observed in severe FXI deficient patients homozygous for p.Glu135* (null allele) upon plasma or FXI concentrate exposure, with a 30% prevalence. The bleeding phenotype was not altered and inhibitors may disappear with time. Adequate haemostasis in the perioperative setting is achievable with low doses of rFVIIa.

Milvexian: evaluating the factor XIa inhibitor for the treatment of acute coronary syndrome

INTRODUCTION

Balancing the prevention of thrombosis with bleeding risk when combining anticoagulants and platelet antagonists remains a concern among clinicians, particularly in patients with acute coronary syndrome (ACS) who are treated with potent antiplatelet therapy. This may be because the available antiplatelet and anticoagulants are unable to uncouple physiological hemostasis and pathological thrombosis. Therefore, their use is associated with an unavoidable elevated risk of bleeding.

AREAS COVERED

Evidence available from studies evaluating FXIa inhibitors and milvexian was collected from a selective literature search. In this review, the authors describe the potential role of FXI/XIa in experimental thrombosis, evidence for FXIa inhibition in the treatment of clinical thrombotic events, and highlight the current evidence supporting the role of milvexian, a novel FXIa inhibitor, in patients with ACS.

EXPERT OPINION

The ongoing LIBREXIA-ACS trial is a large-scale study currently investigating milvexian in patients with ACS. This study may support the proof of concept of differentiating physiological hemostasis and pathological thrombosis and achieving maximum antithrombotic efficacy with minimum bleeding risk when used on top of dual antiplatelet therapy with potent P2Y12 receptor blockers.

Factor XI deficiency: phenotypic age-related considerations and clinical approach towards bleeding risk assessment

ABSTRACT

Factor XI (FXI) deficiency is a rare bleeding disorder that presents complex challenges in patient assessment and bleeding risk management. Despite generally causing mild to moderate bleeding symptoms, clinical manifestations can vary, and bleeding tendency does not always correlate with FXI plasma levels or genotype. Our manuscript delves into the age-related nuances of FXI deficiency across an individual's lifespan. We emphasize issues faced by specific groups, including neonates and females of reproductive age experiencing abnormal uterine bleeding and postpartum hemorrhage. Older patients present unique challenges and concerns related to the management of bleeding as well as thrombotic complications. The current assortment of diagnostic laboratory assays shows limited success in predicting bleeding risk in the perisurgical setting of patients with FXI deficiency. This review explores the intricate interplay between individual bleeding profiles, surgical sites, and FXI activity levels. We also evaluate the accuracy of existing laboratory assays in predicting bleeding and discuss the potential role of investigational global assays in perioperative assessment. Furthermore, we outline our suggested diagnostic approach to refine treatment strategies and decision making. Available treatment options are presented, including antifibrinolytics, replacement products, and recombinant activated FVII. Finally, we discuss promising nonreplacement therapies for the treatment of rare bleeding disorders that can potentially address the challenges faced when managing FXI deficiency-related bleeding complications.

Bleeding phenotype and hemostatic evaluation by thrombin generation in children with Noonan syndrome: A prospective study

BACKGROUND

This study aimed to evaluate the bleeding phenotype and to conduct a comprehensive hemostatic evaluation in individuals with Noonan syndrome (NS), a dominantly inherited disorder caused by pathogenic variants in genes associated with the Ras/MAPK signaling pathway.

METHODS

Children with a genetically confirmed diagnosis of NS underwent clinical evaluation, routine laboratory tests, platelet function testing, and thrombin generation (TG) assessment.

RESULTS

The study included 24 children. The most frequently reported bleeding symptoms were easy bruising and epistaxis, while bleeding complications were observed in 15% of surgical procedures. Various hemostatic abnormalities were identified, including platelet dysfunction, von Willebrand disease, and clotting factor deficiencies. Abnormal platelet function was observed in 50% of the patients, and significantly lower TG parameters were found compared to controls. However, no significant correlation was observed between bleeding symptoms and TG results.

CONCLUSIONS

The study suggests that the bleeding diathesis in NS is multifactorial, involving both platelet dysfunction and deficiencies of plasma coagulation factors. The potential role of TG assay as an ancillary tool for predicting bleeding tendencies in individuals with NS undergoing surgery warrants further investigation.

Factor XI in Carriers of Antiphospholipid Antibodies: Elevated Levels Associated with Symptomatic Thrombotic Cases, While Low Levels Linked to Asymptomatic Cases

Antiphospholipid syndrome (APS) is a thromboinflammatory disorder caused by circulating antiphospholipid autoantibodies (aPL) and characterized by an increased risk of thrombotic events. The pathogenic mechanisms of these antibodies are complex and not fully understood, but disturbances in coagulation and fibrinolysis have been proposed to contribute to the thrombophilic state. This study aims to evaluate the role of an emerging hemostatic molecule, FXI, in the thrombotic risk of patients with aPL. Cross-sectional and observational study of 194 consecutive and unrelated cases with aPL recruited in a single center: 82 asymptomatic (AaPL) and 112 with primary antiphospholipid syndrome (APS). Clinical and epidemiological variables were collected. The profile of aPL was determined. Plasma FXI was evaluated by Western blotting and two coagulation assays (FXI:C). In cases with low FXI, molecular analysis of the F11 gene was performed. FXI:C levels were significantly higher in patients with APS than in patients with AaPL (122.8 ± 33.4 vs. 104.5 ± 27.5; p < 0.001). Multivariate analysis showed a significant association between symptomatic patients with aPL (APS) and high FXI (>150%) (OR = 11.57; 95% CI: 1.47-90.96; p = 0.020). In contrast, low FXI (<70%), mostly caused by inhibitors, was less frequent in the group of patients with APS compared to AaPL (OR = 0.17; 95%CI: 0.36-0.86; p = 0.032). This study suggests that FXI levels may play a causal role in the prothrombotic state induced by aPLs and holds the promise of complementary treatments in APS patients by targeting FXI.

Surgery in rare bleeding disorders: the prospective MARACHI study

Background

Despite the wide use of bleeding scores and the reliability of clotting factor level measurement, bleeding risk stratification before surgery remains challenging in patients with rare inherited bleeding disorders.

Objectives

This multicenter observational prospective study assessed in patients with rare coagulation factor deficiency, the perioperative hemostatic management choices by hemostasis experts and the bleeding outcomes after surgery.

Methods

One hundred seventy-eight patients with low coagulation activity level (factor [F] II, FV, combined FV-FVIII, FVII, FX, or FXI <50%) underwent 207 surgical procedures. The bleeding outcome, Tosetto's bleeding score, and perioperative hemostatic protocols were collected.

Results

Among the 81 procedures performed in patients with severe factor deficiency (level ≤10%), 27 were done without factor replacement (including 6 in patients at high bleeding risk), without any bleeding event. Factor replacement therapy was used mainly for orthopedic procedures. In patients with mild deficiency, 100/126 surgical procedures were carried out without perioperative hemostatic treatment. In patients with FVII or FXI deficiency, factor replacement therapy was in function of the procedure, bleeding risk, and to a lesser extent previous bleeding history. Tranexamic acid was used in almost half of the procedures, particularly in case of surgery in tissues with high fibrinolytic activity (76.8%).

Conclusions

The current perioperative hemostatic management of patients with rare bleeding disorders appears to be adapted. Among the 207 procedures, only 6 were associated with excessive bleeding. Our findings suggest that rather than the bleeding score, factor level and surgery type are the most relevant criteria for perioperative factor replacement therapy.

New Therapeutic Targets for the Prevention and Treatment of Venous Thromboembolism With a Focus on Factor XI Inhibitors

FXI (factor XI) and FXII (factor XII) have emerged as targets for new anticoagulants that have the potential to be both more efficacious and safer than the currently available direct oral anticoagulants for the prevention and treatment of venous thromboembolism. In this review, we discuss the role of FXI and FXII in the pathogenesis of venous thromboembolism, explain why FXI is a better target, and explain why FXI inhibitors have potential advantages over currently available anticoagulants. Finally, we describe the FXI inhibitors under development and discuss their potential to address unmet needs in venous thromboembolism management.

News at XI: moving beyond factor Xa inhibitors

Oral anticoagulants are a mainstay for the prevention and treatment of arterial and venous thrombosis. Direct oral anticoagulants (DOACs) have replaced vitamin K antagonists for many indications. Currently available DOACs include dabigatran, which inhibits thrombin, and apixaban, edoxaban, and rivaroxaban, which inhibit factor (F) Xa. A new class of DOACs is under development. These new DOACs, which include asundexian and milvexian, inhibit FXIa, which is positioned in the intrinsic pathway of coagulation. Anticoagulants that target FXIa have the potential to be safer than the current DOACs because there is emerging evidence that FXI is essential for thrombosis but mostly dispensable for hemostasis. In addition to the oral inhibitors of FXIa, parenteral inhibitors are also under development. These include fesomersen, an antisense oligonucleotide that reduces the hepatic synthesis of FXI; abelacimab, an antibody that binds to FXI and blocks its activation; and osocimab, an FXIa inhibitory antibody. Focusing on these new agents, this article describes the unmet needs in oral anticoagulation therapy, explains why FXI is a promising target for new oral anticoagulants, reviews phase 2 clinical data on new agents, describes ongoing phase 3 trials, and provides a perspective on the opportunities and challenges for FXI inhibitors.

Testing strategies used in the diagnosis of rare inherited bleeding disorders

INTRODUCTION

Rare Bleeding Disorders have a low population prevalence and may not be recognized by most clinicians. In addition, knowledge gaps of the indicated laboratory tests and their availability add to the potential for delayed diagnosis or misdiagnosis. The lack of widely available commercial, regulatory body approved esoteric tests limit them to reference laboratories, thus limiting easy access for patients.

AREAS COVERED

A literature search of Pubmed, Medline, Embase and review of international society guidelines was performed. Additional references from published articles were reviewed. A patient-centered approach to recognition and evaluation of RBD is discussed.

EXPERT OPINION

Recognition of RBD relies on obtaining a detailed patient personal and family hemostatic history. Inquiry into a history of involvement of other organ systems is important and if present should lead to suspicion of an inherited platelet disorder or a variant of Ehlers Danlos Syndrome. Multiple factors contribute to the complexity of development of efficient algorithms for diagnostic testing. Limitations in diagnostic sensitivity and specificity of screening tests, diagnostic tests, and esoteric tests further compound the complexity of establishing a diagnosis. Educational efforts focusing on clinician awareness of RBDs and available testing options are vital for optimal management of such patients.

New pharmacotherapeutic options for oral anticoagulant treatment in atrial fibrillation patients aged 65 and older: factor XIa inhibitors and beyond

INTRODUCTION

Although much progress has been made using anticoagulation for stroke prevention in patients with non-valvular atrial fibrillation, bleeding is still a major concern.

AREAS COVERED

This article reviews current pharmacotherapeutic options in this setting. Particular emphasis is placed on the ability of the new molecules to minimize the bleeding risk in elderly patients. A systematic search of PubMed, Web of Science, and the Cochrane Library up to March 2023 was carried out.

EXPERT OPINION

Contact phase of coagulation is a possible new target for anticoagulant therapy. Indeed, congenital or acquired deficiency of contact phase factors is associated with reduced thrombotic burden and limited risk of spontaneous bleeding. These new drugs seem particularly suitable for stroke prevention in elderly patients with non-valvular atrial fibrillation in whom the hemorrhagic risk is high. Most of anti Factor XI (FXI) drugs are for parenteral use only. A group of small molecules are for oral use and therefore are candidates to substitute direct oral anticoagulants (DOACs) for stroke prevention in elderly patients with atrial fibrillation. Doubts remain on the possibility of impaired hemostasis. Indeed, a fine calibration of inhibition of contact phase factors is crucial for an effective and safe treatment.

Development of new anticoagulant in 2023: Prime time for anti-factor XI and XIa inhibitors

Thrombosis remains one of the leading causes of death in the world. The history of anticoagulation has evolved considerably from non-specific drugs (i.e., heparins and vitamin K antagonists, VKA) to agents that directly target specific coagulation factors (i.e., argatroban, fondaparinux and direct oral anticoagulants, DOAC). Since the last decade, DOAC are widely used in clinical practice because of their ease to use with favorable pharmacological profile and not requiring monitoring, particularly for venous thromboembolism treatment and prevention and stroke prevention in atrial fibrillation. However, despite having a better safety profile than VKA, their bleeding risk is not negligible. Therefore, research is underway to develop new anticoagulant therapies with a better safety profile. One of these news approaches to reduce the risk of bleeding is to target the coagulation in the intrinsic pathway, in particular the contact activation, with the ultimate goal of preventing thrombosis without impairing hemostasis. Based on epidemiological data with patients with inherited factor XI (FXI) deficiency and preclinical studies, FXI emerged as the most promising candidate target separating hemostasis from thrombosis. This review summaries the role of FXI and FXIa in hemostasis, provides evidence of initial success with FXI pathway inhibitors in clinical trials (such as IONIS-FXI_Rx, fesomersen, osocimab, abelacimab, milvexian, asundexian or xisomab 3G3) and highlights the opportunities and challenges for this next generation of anticoagulants.

Global epidemiology of factor XI deficiency: A targeted review of the literature and foundation reports

INTRODUCTION

Hereditary factor XI (FXI) deficiency is a rare coagulation disorder that may result in excessive bleeding requiring intervention to restore haemostasis.

AIM

The aim of this review was to report the current knowledge of the worldwide incidence and prevalence of FXI deficiency.

METHODS

A targeted PubMed search using terms related to FXI deficiency was conducted to identify studies published from April 2002 through April 2022. A manual search supplemented the electronic search. Studies were eligible for data abstraction if they reported population-based incidence proportions/rates or prevalence proportions for FXI deficiency.

RESULTS

The electronic and manual searches returned 253 publications. After applying exclusion criteria, seven publications were included in the analysis, including a global report from the World Federation of Haemophilia (WFH). Six publications provided information on the prevalence of FXI deficiency that included 74 countries and regions. The estimated prevalence of FXI in the WFH report ranged from 0/100,000 in several countries to 55.85/100,000 individuals in the United Kingdom. Prevalence estimates in the PubMed findings ranged from .1 to 246.2/1,000,000 inhabitants with varying methods of case identification and time periods of analysis. One study estimated the incidence of FXI deficiency in Yecla, Spain at 2% of blood donors and .09% of hospital inpatients/outpatients with activated partial thromboplastin time (aPTT) tests.

CONCLUSION

FXI deficiency is rare across the world, but additional steps could be taken to improve incidence and prevalence estimation, for example, development of a consistent FXI deficiency definition and incorporating genetic testing into a clinical routine to better identify and characterise cases.

Tissue factor pathway inhibitor is a potential modifier of bleeding risk in factor XI deficiency

BACKGROUND

Factor (F) XI deficiency is associated with increased bleeding risk in some individuals. Neither FXI levels nor clinical clotting assays predict the bleeding risk. Compared with controls, FXI-deficient bleeders have reduced clot formation, decreased fibrin network density, and increased susceptibility to fibrinolysis. Tissue factor pathway inhibitor (TFPI) was recently implicated as a modifying factor in individuals with bleeding of unknown cause.

OBJECTIVES

To determine the potential of TFPI in modifying the bleeding risk in FXI-deficient individuals.

METHODS

The effects of TFPI on thrombin generation and clot formation, structure, and fibrinolysis in FXI-deficient plasma were measured in vitro in the absence or presence of inhibitory anti-TFPI antibody or exogenous recombinant TFPIα. Total plasma TFPI concentration was measured in 2 independent cohorts of controls and FXI-deficient individuals classified as bleeders or nonbleeders (cohort 1: 10 controls and 16 FXI-deficient individuals; cohort 2: 48 controls and 57 FXI-deficient individuals) and correlated with ex vivo plasma clot formation and fibrinolysis parameters associated with bleeding risk.

RESULTS

In an in vitro FXI deficiency model, inhibition of TFPI enhanced thrombin generation and clot formation, increased the network density, and decreased fibrinolysis, whereas an increase in TFPI had the opposite effects. Compared with controls, plasma from FXI-deficient bleeders had higher TFPI concentration. Total plasma TFPI concentrations correlated with parameters from ex vivo clotting and fibrinolysis assays that differentiate FXI-deficient bleeders and nonbleeders.

CONCLUSION

Coagulation and fibrinolysis parameters that differentiate FXI-deficient nonbleeders and bleeders were altered by plasma TFPIα. Total plasma TFPI was increased in FXI-deficient bleeders. TFPI may modify the bleeding risk in FXI-deficient individuals.

Clinical Evaluation of Factor XIa Inhibitor Drugs: JACC Review Topic of the Week

Factor XI/XIa (FXI/FXIa) represents a potential target for improved precision in anticoagulation because it is involved primarily in thrombus formation and plays a much smaller role in clotting and hemostasis. This suggests that the inhibition of FXI/XIa could prevent pathologic thrombi from forming, but largely preserve a patient's ability to clot in response to bleeding or trauma. This theory is supported by observational data showing that patients with congenital FXI deficiency have lower rates of embolic events without an increase in spontaneous bleeding. Small phase 2 trials of FXI/XIa inhibitors have offered encouraging data with regard to bleeding and safety and evidence of efficacy for the prevention of venous thromboembolism. However, larger clinical trials across multiple patient groups are needed for this emerging class of anticoagulants to understand their possible role in clinical use. Here we review the potential clinical indications for FXI/XIa inhibitors, data available to date, and consider future trials.

Epidural analgesia in a patient with factor XI deficit

FXI deficiency is a rare bleeding disorder characterised by a decreased level or activity of factor. Pregnant women are at increased risk of uterine bleeding during childbirth. Neuroaxial analgesia may increase the risk of epidural hematoma in these patients. However, there is no consensus on the anaesthetic management. We present the clinical case of a 36-year-old woman with a personal history of factor XI deficiency, pregnant with 38 weeks gestation who is scheduled to perform birth induction. Pre-induction factor levels were measured. They were less than 40%, so it was decided to transfuse 20 ml/kg of fresh frozen plasma. After the transfusion it had levels greater than 40%, so epidural analgesia was performed without incident. The patient had no complications secondary to epidural analgesia or transfusion of a high volume of plasma.

Reinvestigation of unidentified causative variants in FXI-deficient patients: Focus on gene segment deletions

INTRODUCTION

Data on failure to identify the molecular mechanism underlying FXI deficiency by Sanger analysis and the contribution of gene segment deletions are almost inexistent.

AIMS AND METHODS

Prospective and retrospective analysis was conducted on FXI-deficient patients' DNA via Next Generation Sequencing (NGS), or Sanger sequencing and Multiplex Probe Ligation-dependent Assay (MLPA) to detect cryptic causative gene variants or gene segment deletions.

RESULTS

Sanger analysis or NGS enabled us to identify six severe and one partial (median activity 41 IU/dl) FXI deficient index cases with deletions encompassing exons 11-15, the whole gene, or both. After Sanger sequencing, retrospective evaluation using MLPA detected seven additional deletion cases in apparently homozygous cases in non-consanguineous families, or in previously unsolved FXI-deficiency cases. Among the 504 index cases with a complete genetic investigation (Sanger/MLPA, or NGS), 23 remained unsolved (no abnormality found [n = 14] or rare intronic variants currently under investigation, [n = 9]). In the 481 solved cases (95% efficiency), we identified F11 gene-deleted patients (14 cases; 2.9%). Among these, whole gene deletion accounted for four heterozygous cases, exons 11-15 deletion for five heterozygous and three homozygous ones, while compound heterozygous deletion and isolated exon 12 deletion accounted for one case each.

CONCLUSION

Given the high incidence of deletions in our population (2.9%), MLPA (or NGS with a reliable bioinformatic pipeline) should be systematically performed for unsolved FXI deficiencies or apparently homozygous cases in non-consanguineous families.

Molecular basis of rare congenital bleeding disorders

Rare bleeding disorders (RBDs), including factor (F) I, FII, FV, FVII, combined FV and FVIII (CF5F8), FXI, FXIII and vitamin-K dependent coagulation factors (VKCF) deficiencies, are a heterogeneous group of hemorrhagic disorder with a variable bleeding tendency. RBDs are due to mutation in underlying coagulation factors genes, except for CF5F8 and VKCF deficiencies. FVII deficiency is the most common RBD with >330 variants in the F7 gene, while only 63 variants have been identified in the F2 gene. Most detected variants in the affected genes are missense (>50% of all RBDs), while large deletions are the rarest, having been reported in FVII, FX, FXI and FXIII deficiencies. Most were located in the catalytic and activated domains of FXI, FX, FXIII and prothrombin deficiencies. Understanding the proper molecular basis of RBDs not only can help achieve a timely and cost-effective diagnosis, but also can help to phenotype properties of the disorders.

Liver-heart cross-talk mediated by coagulation factor XI protects against heart failure

Tissue-tissue communication by endocrine factors is a vital mechanism for physiologic homeostasis. A systems genetics analysis of transcriptomic and functional data from a cohort of diverse, inbred strains of mice predicted that coagulation factor XI (FXI), a liver-derived protein, protects against diastolic dysfunction, a key trait of heart failure with preserved ejection fraction. This was confirmed using gain- and loss-of-function studies, and FXI was found to activate the bone morphogenetic protein (BMP)-SMAD1/5 pathway in the heart. The proteolytic activity of FXI is required for the cleavage and activation of extracellular matrix-associated BMP7 in the heart, thus inhibiting genes involved in inflammation and fibrosis. Our results reveal a protective role of FXI in heart injury that is distinct from its role in coagulation.

VhH anti-thrombomodulin clone 1 inhibits TAFI activation and enhances fibrinolysis in human whole blood under flow

BACKGROUND

Thrombomodulin on endothelial cells can form a complex with thrombin. This complex has both anticoagulant properties, by activating protein C, and clot-protective properties, by activating thrombin-activatable fibrinolysis inhibitor (TAFI). Activated TAFI (TAFIa) inhibits plasmin-mediated fibrinolysis.

OBJECTIVES

TAFIa inhibition is considered a potential antithrombotic strategy. So far, this goal has been pursued by developing compounds that directly inhibit TAFIa. In contrast, we here describe variable domain of heavy-chain-only antibody (VhH) clone 1 that inhibits TAFI activation by targeting human thrombomodulin.

METHODS

Two llamas (Lama Glama) were immunized, and phage display was used to select VhH anti-thrombomodulin (TM) clone 1. Affinity was determined with surface plasmon resonance and binding to native TM was confirmed with flow cytometry. Clone 1 was functionally assessed by competition, clot lysis, and thrombin generation assays. Last, the effect of clone 1 on tPA-mediated fibrinolysis in human whole blood was investigated in a microfluidic fibrinolysis model.

RESULTS

VhH anti-TM clone 1 bound recombinant TM with a binding affinity of 1.7 ± 0.4 nM and showed binding to native TM. Clone 1 competed with thrombin for binding to TM and attenuated TAFI activation in clot lysis assays and protein C activation in thrombin generation experiments. In a microfluidic fibrinolysis model, inhibition of TM with clone 1 fully prevented TAFI activation.

DISCUSSION

We have developed VhH anti-TM clone 1, which inhibits TAFI activation and enhances tPA-mediated fibrinolysis under flow. Different from agents that directly target TAFIa, our strategy should preserve direct TAFI activation via thrombin.

A Common Missense Variant Causing Factor XI Deficiency and Increased Bleeding Tendency in Maine Coon Cats

Hereditary factor XI (FXI) deficiency is characterized as an autosomal mild to moderate coagulopathy in humans and domestic animals. Coagulation testing revealed FXI deficiency in a core family of Maine Coon cats (MCCs) in the United States. Factor XI-deficient MCCs were homozygous for a guanine to adenine transition resulting in a methionine substitution for the highly conserved valine-516 in the FXI catalytic domain. Immunoblots detected FXI of normal size and quantity in plasmas of MCCs homozygous for V516M. Some FXI-deficient MCCs experienced excessive post-operative/traumatic bleeding. Screening of 263 MCCs in Europe revealed a mutant allele frequency of 0.232 (23.2%). However, V516M was not found among 100 cats of other breeds. Recombinant feline FXI-M516 (fFXI-M516) expressed ~4% of the activity of wild-type fFXI-V516 in plasma clotting assays. Furthermore, fFXIa-M516 cleaved the chromogenic substrate S-2366 with ~4.3-fold lower catalytic efficacy (kcat/Km) than fFXIa-V516, supporting a conformational alteration of the protease active site. The rate of FIX activation by fFXIa-M516 was reduced >3-fold compared with fFXIa-V516. The common missense variant FXI-V516M causes a cross-reactive material positive FXI deficiency in MCCs that is associated with mild-moderate bleeding tendencies. Given the prevalence of the variant in MCCs, genotyping is recommended prior to invasive procedures or breeding.

Safety of the oral factor XIa inhibitor asundexian compared with apixaban in patients with atrial fibrillation (PACIFIC-AF): a multicentre, randomised, double-blind, double-dummy, dose-finding phase 2 study

BACKGROUND

Direct-acting oral anticoagulant use for stroke prevention in atrial fibrillation is limited by bleeding concerns. Asundexian, a novel, oral small molecule activated coagulation factor XIa (FXIa) inhibitor, might reduce thrombosis with minimal effect on haemostasis. We aimed to determine the optimal dose of asundexian and to compare the incidence of bleeding with that of apixaban in patients with atrial fibrillation.

METHODS

In this randomised, double-blind, phase 2 dose-finding study, we compared asundexian 20 mg or 50 mg once daily with apixaban 5 mg twice daily in patients aged 45 years or older with atrial fibrillation, a CHA₂DS₂-VASc score of at least 2 if male or at least 3 if female, and increased bleeding risk. The study was conducted at 93 sites in 14 countries, including 12 European countries, Canada, and Japan. Participants were randomly assigned (1:1:1) to a treatment group using an interactive web response system, with randomisation stratified by whether patients were receiving a direct-acting oral anticoagulant before the study start. Masking was achieved using a double-dummy design, with participants receiving both the assigned treatment and a placebo that resembled the non-assigned treatment. The primary endpoint was the composite of major or clinically relevant non-major bleeding according to International Society on Thrombosis and Haemostasis criteria, assessed in all patients who took at least one dose of study medication. This trial is registered with ClinicalTrials.gov, NCT04218266, and EudraCT, 2019-002365-35.

FINDINGS

Between Jan 30, 2020, and June 21, 2021, 862 patients were enrolled. 755 patients were randomly assigned to treatment. Two patients (assigned to asundexian 20 mg) never took any study medication, resulting in 753 patients being included in the analysis (249 received asundexian 20 mg, 254 received asundexian 50 g, and 250 received apixaban). The mean age of participants was 73·7 years (SD 8·3), 309 (41%) were women, 216 (29%) had chronic kidney disease, and mean CHA₂DS₂-VASc score was 3·9 (1·3). Asundexian 20 mg resulted in 81% inhibition of FXIa activity at trough concentrations and 90% inhibition at peak concentrations; asundexian 50 mg resulted in 92% inhibition at trough concentrations and 94% inhibition at peak concentrations. Ratios of incidence proportions for the primary endpoint were 0·50 (90% CI 0·14-1·68) for asundexian 20 mg (three events), 0·16 (0·01-0·99) for asundexian 50 mg (one event), and 0·33 (0·09-0·97) for pooled asundexian (four events) versus apixaban (six events). The rate of any adverse event occurring was similar in the three treatment groups: 118 (47%) with asundexian 20 mg, 120 (47%) with asundexian 50 mg, and 122 (49%) with apixaban.

INTERPRETATION

The FXIa inhibitor asundexian at doses of 20 mg and 50 mg once daily resulted in lower rates of bleeding compared with standard dosing of apixaban, with near-complete in-vivo FXIa inhibition, in patients with atrial fibrillation.

FUNDING

Bayer.

Pediatric severe factor XI deficiency: A multicenter study

BACKGROUND

Factor XI (FXI) deficiency is a rare autosomal recessive bleeding disorder. Only scarce publications address its clinical features in children. The increased prevalence of FXI deficiency in Israel enabled data collection for this large multicenter cohort study.

OBJECTIVE

Some hemostatic challenges may be unique or more common in children, such as bleeding in the neonatal period or trauma-related injury. The current study was designed to explore the potential impact of these differences in children with severe FXI deficiency.

METHODS

Medical files of all children with FXI level under 15% followed at five tertiary centers were evaluated. The retrieved data comprised demographic and clinical characteristics, including bleeding episodes, surgical interventions, treatment strategies, as well as laboratory features.

RESULTS

Sixty children, whose median age at diagnosis was 4.2 years and their median FXI level was 4%, were included. Three children experienced triggered intracranial hemorrhage (ICH) and two children had major bleeds. No bleeding complications occurred in surgeries in which hemostatic treatment consisting mostly of tranexamic acid or fresh frozen plasma was applied (n = 45). In contrast, excessive bleeding was noted in 25% of surgical procedures performed without hemostatic preparation (p = .002).

CONCLUSION

This study's findings confirm the generally favorable outcome of this rare bleeding disorder, with no spontaneous bleeds or cases of perinatal ICH. Nonetheless, proper diagnosis and adequate hemostasis in the surgical setting are imperative. Unlike previous studies in adults, our pediatric study suggests an association between the severity of FXI deficiency and bleeding tendency.

Structural insights into the activation of blood coagulation factor XI zymogen by thrombin: A computational molecular dynamics study

Activation of human blood coagulation factor XI zymogen to factor XIa plays a significant role in the upstream coagulation pathway, in which factor XIa activates factor IX zymogen. The mechanistic details of the proteolytic activation of factor XI by the activating enzyme thrombin are not well-understood at atomic level. In this study, we employed a combination of molecular docking and microsecond time-scale molecular dynamics simulations to identify the key regions of interaction between fXI and thrombin. The activating complex between the substrate and enzyme was modeled to represent the initial acylation step of the serine-protease hydrolysis mechanism. The proposed solution structural complex, fIX:fIIa, obtained from 3 microseconds of MD refinement, suggests that the activation of factor XI is mediated by thrombin's anion binding exosite-II interactions with A3 and A4 domains. We predict that the two positively charged arginine residues (Arg409 and Arg413) in the exosite-2 region, the β- and γ-insertion loops of thrombin play an important structural role in the initial activating complex between fXI and thrombin.

Human coagulation factor IX: a systematic review of its characteristics

Human coagulation factor IX (FIX) is a vitamin K dependent glycoprotein. It is used in therapy of factor IX deficiency, known as haemophilia B. This article explained the coagulation process involved in FIX and the principle of haemophilia B caused by its absence. We searched and aligned the sequence information of IX in the NCBI's EST database to predict its structure and understand the molecular biological basis of its function. Further, by sorting out the development history of FIX, we summarized the general process of its isolation and purification. Finally, the clinical indications and complications of FIX were overviewed. Through a comprehensive description of the characteristics of FIX, we hope to give readers a clear understanding and put forward our views on the future development of the product.

The Association between Factor XI Deficiency and the Risk of Bleeding, Cardiovascular, and Venous Thromboembolic Events

The objective of this study was to assess the relationship between factor XI (FXI) deficiency and the risks of bleeding and cardiovascular (CV) events. We conducted a retrospective cohort study using data from Maccabi Healthcare Services (MHS). We identified adults with FXI deficiency (severe: <15%, partial: 15 to <50%, any deficiency: <50%) that had been tested for FXI between 2007 and 2018 and matched to patients from the general MHS population. We estimated 10-year risks of outcomes using the Kaplan–Meier approach. Using Cox proportional hazards regression, we compared outcomes among patients with versus without FXI deficiency. Less than 10% of patients tested for FXI activity had activity levels <50% (mean age: 39 years; 72.2% females). Compared with the general population, patients with any FXI deficiency were at higher risk of severe bleeding (adjusted hazard ratio [aHR]: 2.56, 95% confidence interval [CI]: 1.13–5.81; 10-year risk: 1.90%, 95% CI: 0.50–3.20% vs. 0.90%, 95% CI: 0.50–1.30%) and clinically relevant nonsevere bleeding (CRNSB) (aHR: 1.45, 95% CI: 1.08–1.97; 10-year risk: 11.60%, 95% CI: 8.30–14.80% vs. 9.20%, 95% CI: 8.00–10.40%). Severe FXI deficiency was associated with a greater risk of CRNSB. While few CV events ( N  = 2) and venous thromboembolisms (VTE) ( N  = 1) were observed in the FXI overall deficient group, there was a nonsignificant negative association between any FXI deficiency and CV events (aHR: 0.55; 95% CI: 0.13–2.36) and VTEs (aHR: 0.45; 95% CI: 0.06–3.47). Overall FXI deficiency was associated with an increased risk of severe bleeding and CRNSB. Further research is warranted to explore the lower risk of CV and VTE among patients with FXI deficiency compared with the general population.

Approach to the Patient with Bleeding

Approach to the patient with bleeding begins with a thorough bleeding, medical, and family history to determine the nature of bleeding and severity of bleeding symptoms. Use of a Bleeding Assessment Tool allows the clinician to obtain a comprehensive bleeding history and ultimately determine the individual bleeding score that reflects bleeding severity and is classifiable as either normal or abnormal. In the absence of significant findings within patient history or presenting symptoms clearly pointing to a specific bleeding pathology, an approach to laboratory investigation is presented that proceeds through first-line, second-line, and third-line testing.

Factor XI Deficiency

Factor XI (FXI) deficiency (hemophilia C or Rosenthal disease) was first described in the 1950s in a multigenerational family experiencing bleeding related to surgery and dental procedures. Managing patients with FXI deficiency presents several challenges, including a lack of correlation of bleeding symptoms with FXI activity levels, the large volume of fresh frozen plasma required to achieve hemostatic FXI levels, lack of availability of FXI concentrate in certain regions of the world, and the inherent thrombotic risk associated with replacement therapy. This article summarizes presentation, diagnosis, and management of patients with FXI deficiency in a variety of clinical settings.

Blood Clotting and the Pathogenesis of Types I and II Hereditary Angioedema

The plasma contact system is the initiator of the intrinsic pathway of coagulation and the main producer of the inflammatory peptide bradykinin. When plasma is exposed to a negatively charged surface the two enzymes factor XII (FXII) and plasma prekallikrein (PK) bind to the surface alongside the co-factor high molecular weight kininogen (HK), where PK is non-covalently bound to. Here, FXII and PK undergo a reciprocal activation feedback loop that leads to full contact system activity in a matter of seconds. Although naturally occurring negatively charged surfaces have shown to be involved in the role of the contact system in thrombosis, such surfaces are elusive in the pathogenesis of bradykinin-driven hereditary angioedema (HAE). In this review, we will explore the molecular mechanisms behind contact system activation, their assembly on the endothelial surface, and their role in the HAE pathophysiology.

Pharmacological targeting of coagulation factor XI mitigates the development of experimental atherosclerosis in low-density lipoprotein receptor-deficient mice

BACKGROUND

Human coagulation factor (F) XI deficiency, a defect of the contact activation system, protects against venous thrombosis, stroke, and heart attack, whereas FXII, plasma prekallikrein, or kininogen deficiencies are asymptomatic. FXI deficiency, inhibition of FXI production, activated FXI (FXIa) inhibitors, and antibodies to FXI that interfere with FXI/FXII interactions reduce experimental thrombosis and inflammation. FXI inhibitors are antithrombotic in patients, and FXI and FXII deficiencies are atheroprotective in apolipoprotein E-deficient mice.

OBJECTIVES

Investigate the effects of pharmacological targeting of FXI in experimental models of atherogenesis and established atherosclerosis.

METHODS AND RESULTS

Low-density lipoprotein receptor-knockout (Ldlr-/- ) mice were administered high-fat diet (HFD) for 8 weeks; concomitantly, FXI was targeted with anti-FXI antibody (14E11) or FXI antisense oligonucleotide (ASO). 14E11 and FXI-ASO reduced atherosclerotic lesion area in proximal aortas when compared with controls, and 14E11 also reduced aortic sinus lesions. In an established disease model, in which therapy was given after atherosclerosis had developed, Ldlr-/- mice were fed HFD for 8 weeks and then administered 14E11 or FXI-ASO weekly until 16 weeks on HFD. In this established disease model, 14E11 and FXI-ASO reduced atherosclerotic lesion area in proximal aortas, but not in aortic sinus. In cultures of human endothelium, FXIa exposure disrupted VE-Cadherin expression and increased endothelial lipoprotein permeability. Strikingly, we found that 14E11 prevented the disruption of VE-Cadherin expression in aortic sinus lesions observed in the atherogenesis mouse model.

CONCLUSION

Pharmacological targeting of FXI reduced atherogenesis in Ldlr-/- mice. Interference with the contact activation system may safely reduce development or progression of atherosclerosis.

The rebirth of the contact pathway: a new therapeutic target

PURPOSE OF REVIEW

Anticoagulation with vitamin-K antagonists or direct oral anticoagulants is associated with a significant risk of bleeding. There is a major effort underway to develop antithrombotic drugs that have a smaller impact on hemostasis. The plasma contact proteins factor XI (FXI) and factor XII (FXII) have drawn considerable interest because they contribute to thrombosis but have limited roles in hemostasis. Here, we discuss results of preclinical and clinical trials supporting the hypothesis that the contact system contributes to thromboembolic disease.

RECENT FINDINGS

Numerous compounds targeting FXI or FXII have shown antithrombotic properties in preclinical studies. In phase 2 studies, drugs-targeting FXI or its protease form FXIa compared favorably with standard care for venous thrombosis prophylaxis in patients undergoing knee replacement. While less work has been done with FXII inhibitors, they may be particularly useful for limiting thrombosis in situations where blood comes into contact with artificial surfaces of medical devices.

SUMMARY

Inhibitors of contact activation, and particularly of FXI, are showing promise for prevention of thromboembolic disease. Larger studies are required to establish their efficacy, and to establish that they are safer than current therapy from a bleeding standpoint.

Identification of an alpha-1 antitrypsin variant with enhanced specificity for factor XIa by phage display, bacterial expression, and combinatorial mutagenesis

Coagulation Factor XIa (FXIa) is an emerging target for antithrombotic agent development. The M358R variant of the serpin alpha-1 antitrypsin (AAT) inhibits both FXIa and other proteases. Our aim was to enhance the specificity of AAT M358R for FXIa. We randomized two AAT M358R phage display libraries at reactive centre loop positions P13-P8 and P7-P3 and biopanned them with FXIa. A bacterial expression library randomized at P2′-P3′ was also probed. Resulting novel variants were expressed as recombinant proteins in E. coli and their kinetics of FXIa inhibition determined. The most potent FXIa-inhibitory motifs were: P13-P8, HASTGQ; P7-P3, CLEVE; and P2-P3′, PRSTE (respectively, novel residues bolded). Selectivity for FXIa over thrombin was increased up to 34-fold versus AAT M358R for these single motif variants. Combining CLEVE and PRSTE motifs in AAT-RC increased FXIa selectivity for thrombin, factors XIIa, Xa, activated protein C, and kallikrein by 279-, 143-, 63-, 58-, and 36-fold, respectively, versus AAT M358R. AAT-RC lengthened human plasma clotting times less than AAT M358R. AAT-RC rapidly and selectively inhibits FXIa and is worthy of testing in vivo. AAT specificity can be focused on one target protease by selection in phage and bacterial systems coupled with combinatorial mutagenesis.

Monogenic Causes of Apparently Idiopathic Perinatal Intracranial Hemorrhage

OBJECTIVE

Perinatal intracranial hemorrhage (pICH) is a rare event that occurs during the fetal/neonatal period with potentially devastating neurological outcome. However, the etiology of pICH is frequently hard to depict. We investigated the role of rare genetic variations in unexplained cases of pICH.

METHODS

We performed whole-exome sequencing (WES) in fetuses and term neonates with otherwise unexplained pICH and their parents. Variant causality was determined according to the American College of Medical Genetics and Genomics (ACMG) criteria, consistency between suggested genes and phenotypes, and mode of inheritance.

RESULTS

Twenty-six probands (25 families) were included in the study (9 with a prenatal diagnosis and 17 with a postnatal diagnosis). Intraventricular hemorrhage (IVH) was the most common type of hemorrhage (n = 16, 62%), followed by subpial (n = 4, 15%), subdural (n = 4, 15%), and parenchymal (n = 2, 8%) hemorrhage. Causative/likely causative variants were found in 4 subjects from 3 of the 25 families (12%) involving genes related to the brain microenvironment (COL4A1, COL4A2, and TREX-1). Additionally, potentially causative variants were detected in genes related to coagulation (GP1BA, F11, Von Willebrand factor [VWF], FGA, and F7; n = 4, 16%). A potential candidate gene for phenotypic expansion related to microtubular function (DNAH5) was identified in 1 case (4%). Fifty-five percent of the variants were inherited from an asymptomatic parent. Overall, these findings showed a monogenic cause for pICH in 12% to 32% of the families.

INTERPRETATION

Our findings reveal a clinically significant diagnostic yield of WES in apparently idiopathic pICH and support the use of WES in the evaluation of these cases. ANN NEUROL 2021;89:813-822.

Osocimab: A Novel Agent in Preventing Venous Thromboembolism

The nature of orthopedic surgery, and specifically total knee arthroplasty, lends itself to the development of venous thromboembolism given endothelial injury from the surgical procedure, promotion of an acute hypercoagulable state, and the prolonged period of immobilization after surgery promoting stasis; all factors of Virchow's triad. Current guidelines recommend the direct acting oral anticoagulants, enoxaparin, fondaparinux, and warfarin as options for venous thromboembolism prevention. However, these agents may still be prone to unacceptable bleeding risk, given they mostly target the extrinsic pathway of the clotting cascade, and have other characteristics which can be problematic for use. Investigators have determined patients with factor XI deficiency seem to be protected for thrombotic risk and seem to be devoid of bleeding sequelae. This has led to the development of osocimab, a fully humanized monoclonal G1 antibody designed specifically to functionally neutralize factor XIa. Phase 1 clinical trials have demonstrated an agent with a long half-life (∼30 days) with minimal requirement of renal elimination and hepatic metabolism. Phase 2 trials have identified that an optimal dose range, 0.6-1.2 mg/kg, as a 1-time dose preoperatively or postoperatively is effective in preventing thrombotic complications with minimal bleeding risk compared with standard of care for elective total knee arthroplasty patients. Future clinical development will be able to clearly outline the role this agent will play in the future.

How to Assess Founder Effect in Patients with Congenital Factor XIII Deficiency

Congenital factor XIII (FXIII) deficiency is an extremely rare bleeding disorder (RBD) with estimated prevalence of one per 2 million in the general population. The disorder causes different clinical manifestations such as intracranial hemorrhage (ICH), recurrent miscarriage, umbilical cord bleeding, etc. High incidence of the disorder might be due to founder effect. To assess founder effect, haplotype analysis is an important step. For this purpose, suitable and reliable genetic markers such as microsatellites (Hum FXIIIA01 and HumFXIIIA02) and single nucleotide polymorphisms (SNP) are suggested. In the present study we tried to describe evaluation of founder effect in patients with congenital FXIII deficiency via haplotype analysis using suitable genetic markers.

The clinical management of factor XI deficiency in pregnant women

INTRODUCTION

Factor XI (FXI) deficiency is associated with highly variable bleeding, including excessive gynecologic and obstetrical bleeding. Since approximately 20% of FXI-deficient women will experience pregnancy-related bleeding, careful planning and knowledge of appropriate hemostatic management is pivotal for their care.

AREAS COVERED

In this manuscript, authors present our current understanding of the role of FXI in hemostasis, the nature of the bleeding phenotype caused by its deficiency, and the impact of deficiency on obstetrical care. The authors searched PubMed with the terms, 'factor XI', 'factor XI deficiency', 'women', 'pregnancy', and 'obstetrics' to identify literature on these topics. Expectations of pregnancy-related complications in women with FXI deficiency, including antepartum, abortion-related, and postpartum bleeding, as well as bleeding associated with regional anesthesia are discussed. Recommendations for the care of these women are considered, including guidance for management of prophylactic care and acute bleeding.

EXPERT COMMENTARY

FXI deficiency results in a bleeding diathesis in some, but not all, patients, making treatment decisions and clinical management challenging. Currently available laboratory assays are not particularly useful for distinguishing patients with FXI deficiency who are prone to bleeding from those who are not. There is a need for alternative testing strategies to address this limitation.

Peri- and Postpartum Management of Patients With Factor XI Deficiency

Factor XI (FXI) deficiency is an uncommon autosomal disorder with variable bleeding phenotype, making peripartum management challenging. We describe our experience in pregnant women with FXI deficiency and identify strategies to minimize the use of hemostatic agents and increase utilization of neuraxial anesthesia. Electronic records of 28 pregnant women with FXI deficiency seen by a hematology service in an academic medical center from January 2006 to August 2018 were reviewed. Data on bleeding, obstetric history, peripartum management, and FXI activity were collected. Partial FXI deficiency was defined as >20 IU/dL and severe <20 IU/dL. Median FXI activity was 42 IU/dL (range <1-73 IU/dL), and median activated partial thromboplastin time was 32.2 seconds (range: 27.8-75 seconds). There were 64 pregnancies: 53 (83%) live births and 11 (17%) pregnancy losses. Postpartum hemorrhage occurred in 9 (17%) pregnancies. Antifibrinolytic agents and fresh frozen plasma were used only in women with severe deficiency (42% with bleeding and 17% with no bleeding phenotype, respectively). Neuraxial anesthesia was successfully administered in 32 (59%) deliveries. Most women with FXI deficiency have uncomplicated pregnancies and deliveries with minimal hemostatic support. Neuraxial anesthesia can be safely administered in most women.

Inhibition of contact-mediated activation of factor XI protects baboons against S aureus-induced organ damage and death

Staphylococcus aureus infections can produce systemic bacteremia and inflammation in humans, which may progress to severe sepsis or septic shock, even with appropriate antibiotic treatment. Sepsis may be associated with disseminated intravascular coagulation and consumptive coagulopathy. In some types of mouse infection models, the plasma coagulation protein factor XI (FXI) contributes to the pathogenesis of sepsis. We hypothesize that FXI also contributes to the pathogenesis of sepsis in primates, and that pharmacological interference with FXI will alter the outcome of Staphylococcus aureus-induced lethality in a baboon model. Pretreatment of baboons with the anti-FXI antibody 3G3, a humanized variant of the murine monoclonal 14E11 that blocks FXI activation by FXIIa, substantially reduced the activation of coagulation, as reflected by clotting times and plasma complexes of coagulation proteases (FXIIa, FXIa, FIXa, FXa, FVIIa, and thrombin) with serpins (antithrombin or C1 inhibitor) following infusion of heat-inactivated S aureus 3G3 treatment reduced fibrinogen and platelet consumption, fibrin deposition in tissues, neutrophil activation and accumulation in tissues, cytokine production, kininogen cleavage, cell death, and complement activation. Overall, 3G3 infusion protected the structure and function of multiple vital organs, including lung, heart, liver, and kidney. All treated animals reached the end point survival (7 days), whereas all nontreated animals developed terminal organ failure within 28 hours. We conclude that FXI plays a role in the pathogenesis of S aureus-induced disseminated intravascular coagulation and lethality in baboons. The results provide proof of concept for future therapeutic interventions that may prevent sepsis-induced organ failure and save lives in certain forms of sepsis.

Evaluation of Abnormal Bleeding in Children

Abnormal bleeding or bruising is a relatively common clinical concern, frequently causing parents to seek care from their children's primary care provider. Although ecchymosis from playful trauma, occasional epistaxis, and heavy menstrual bleeding around the time of menarche and beyond are common occurrences, it can be difficult for pediatricians and other primary care providers to determine if their patient has age-appropriate symptoms versus abnormal or excessive bleeding. This review discusses considerations for abnormal bleeding in pediatrics and discusses an initial approach for evaluation of hemostasis in a child with bleeding symptoms. [Pediatr Ann. 2020;49(1):e36-e42.].

The Evolving Dilemma of Factor XI in Pregnancy: Suggestions for Management

A case of a patient with severe factor XI (FXI) deficiency who presented for her seventh labor and delivery is presented. The nature of FXI deficiency, its prevalence, and issues related to genetic screening are discussed. Published literature on the topic is reviewed, including criteria that were developed to assess bleeding, laboratory tools used to estimate bleeding risk, and available treatments. Within the context of this challenging clinical dilemma, specific recommendations are provided for the antepartum, intrapartum, and postpartum stages of pregnancy. These include recommendations that take into account both FXI levels and history of any abnormal bleeding. While there are effective treatments available, it is important to consider that institutional multidisciplinary protocols are needed to manage this complex disorder. More work is needed to define the best management protocols.

A successful case of laparoscopic colorectal cancer resection in an elderly patient with factor XI deficiency

Background

Congenital XI factor deficiency is a rare disease caused by autosomal recessive inheritance. Clinically, there are few spontaneous hemorrhages, which can cause abnormal bleeding after trauma, surgery, and tooth extraction. We experienced a colon cancer patient with congenital XI factor deficiency who was successfully treated by laparoscopic approach with the administration of the preoperative fresh frozen plasma (FFP).

Case presentation

The patient was an 82-year-old woman who complained of right lower abdominal pain for a period of 2 months with no previous history of abnormal hemostasis. She received colonoscopy and was diagnosed with ascending colon cancer. Preoperative blood tests resulted in prolongation of activated partial thromboplastin time (APTT). After further investigation, factor XI (FXI) activity was found to be abnormal at 3.0% and congenital FXI deficiency was diagnosed. By replenishing FXI by FFP, APTT was improved to 37 s so perioperative abnormal bleeding could be avoided and an operation for ascending colon cancer performed. The patient received laparoscopic ileocolic resection and was discharged on a postoperative day 7 uneventfully.

Conclusion

It is important to detect coagulation disorders such as FXI deficiency during routine preoperative checkups, and it is also important to consider unrecognized coagulation disorders if we encounter unexplained abnormal bleeding after surgery or trauma. In patients who have already been diagnosed with FXI deficiency, appropriate treatment including administration of FFP should be considered before surgery, and laparoscopic approach has a possibility to bring safety outcomes as an effect of the reduction of the intraoperative bleeding.

Emicizumab, the bispecific antibody to factors IX/IXa and X/Xa, potentiates coagulation function in factor XI-deficient plasma in vitro

Essentials Emicizumab mimics factor (F)VIIIa cofactor function, augments the intrinsic tenase activity. We assessed the emicizumab-driven hemostatic function in FXI-deficient plasmas. Emicizumab improved the coagulation potentials in severe FXI-deficient plasma. Emicizumab may provide a possibility for clinical application in patients with FXI deficiency. SUMMARY: Background Patients with factor (F)XI deficiency commonly present with markedly prolonged activated partial thromboplastin times (APTT), although bleeding phenotypes are heterogeneous. Emicizumab, a bispecific monoclonal antibody to FIX/FIXa and FX/FXa, mimics FVIIIa cofactor function on phospholipid (PL) surfaces. Antibody reactions were designed, therefore, to augment mechanisms during the propagation phase of blood coagulation. Aim To assess emicizumab-driven hemostatic function in FXI-deficient plasmas. Methods and Results Standard ellagic acid (Elg)/PL-based APTTs of different FXI-deficient plasmas (n = 13; FXI activity, < 1 IU dl-1 ) were markedly shortened dose dependently by the presence of emicizumab. To further analyze the effects of emicizumab, clot waveform analysis (CWA) in FXI-deficient plasmas with emicizumab, triggered by tissue factor (TF)/Elg demonstrated improvements in both clot times, reflecting the initiation phase, and coagulation velocity, which represents the propagation phase. Emicizumab also enhanced the TF/Elg-triggered thrombin generation in FXI-deficient plasmas dose-dependently although the degree of enhancement varied in individual cases. Thrombin generation with either FVII-deficient plasma or FIX-deficient plasma treated with anti-FXI antibody showed little or no increase by the co-presence of emicizumab, suggesting that the accelerated thrombin generation in FXI-deficient plasmas by emicizumab should depend on the FIXa-involved coagulation propagation initially triggered by FVIIa/TF. The ex vivo addition of emicizumab to whole blood from three patients with severe FXI deficiency demonstrated modest, dose-dependent improvements in Ca2+ -triggered thromboelastograms (NATEM mode). Conclusion Emicizumab appeared to improve coagulation function in severe FXI-deficient plasma, and might provide possibilities for clinical application in patients with FXI deficiency.