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

Identification and characterization of factor XI autoantibodies in 2 patients with systemic lupus erythematosus: insights into mechanisms of acquired factor XI deficiency

Background

Factor (F)XI is a zymogen that contributes to thrombin generation through activation of FIX. Patients with a complete absence of FXI are prone to developing alloantibody inhibitors after replacement therapy. Acquired FXI autoantibodies are less common, and data regarding their mechanisms of action are lacking.

Objectives

We describe 2 patients with severe acquired FXI deficiency and identify the FXI domains to which the autoantibodies bind.

Methods

FXI and prekallikrein (PK) are homologs with similar structures. We prepared recombinant human FXI and PK, as well as chimeric molecules in which individual domains within FXI or PK are replaced with the corresponding domain from the other protein. Patient plasma and normal plasma were used as antibody sources, and their capacities to recognize recombinant proteins on Western blots were compared.

Results

Patients 1 and 2 were females with systemic lupus erythematous and no bleeding history. FXI activity in both cases was undetectable by one-stage clotting assay, with autoantibody titers of 64 Bethesda Units and 11.4 Bethesda Units, respectively. In both cases, the autoantibody appeared to clear FXI protein from plasma. Immunoglobulin G in patient 1 targeted the FXI catalytic domain, while the autoantibody in patient 2 was likely oligoclonal with components that recognized the FXI apple 2 and apple 3 domains.

Conclusion

These autoantibodies inhibited FXI function and promoted its clearance. The inhibitors targeted the 2 most important FXIa domains for FIX activation and demonstrated properties similar to those described in patients with FXI alloantibody inhibitors.

Case Report: Allelic and biallelic variants in coagulation factor XI cause factor XI deficiency

Factor XI deficiency is a rare inherited coagulation disorder with an estimated prevalence of affecting 1 in 1 million. It is characterized by mild and variable bleeding phenotypes, including bruises, nosebleeds, hematuria, and postpartum hemorrhage. It can be caused by either allelic or biallelic variants in coagulation factor XI (F11). Coagulation factor XI is a glycoprotein that circulates in plasma as a non-covalent complex with high-molecular-weight kininogen. It is converted to an active protease, coagulation factor XIa, which participates in blood coagulation as a catalyst. In this study, we recruited a family with Factor XI deficiency and identified two F11 variants using whole-exome sequencing. One (NM_000128.4: c.841C>T, p.Q281X) was a known variant, and the other (NM_000128.4: c.1832T>G, p.V611G) had not been reported. In addition, we compiled the characteristics of known missense variants in coagulation factor XI. Our findings enriched the variant spectrum of Factor XI deficiency and contributed to the genetic counseling and molecular diagnostics of Factor XI deficiency.

Novel horizons in anticoagulation: the emerging role of factor XI inhibitors across different settings

Anticoagulants have long been fundamental in preventing and treating thromboembolic disorders, with a recent shift of focus towards direct oral anticoagulants, thanks to their ease of use, efficacy, and safety. Despite these advancements, bleeding complications remain a major concern with any anticoagulant, highlighting the need for safer drugs. Factor XI (FXI) inhibitors have emerged as promising agents in this regard, offering a novel approach by targeting upstream factors in the coagulation system. Phase II trials have shown encouraging outcomes, indicating a reduced bleeding risk compared to that associated with traditional anticoagulants, particularly in the context of cardiovascular disease management when combined with antiplatelet therapy. However, the variability in findings and limited efficacy data call for a cautious interpretation pending insights from phase III trials. These trials are essential for validating the potential of FXI inhibitors to balance bleeding risk reduction and maintain anticoagulant efficacy. This review explores the pharmacology, potential indications, clinical data, and future directions of FXI inhibitors, providing a perspective on their evolving role in anticoagulant therapy. It also provides a detailed analysis of data from published clinical trials on FXI inhibitors in various indications. Preliminary data from ongoing trials are also outlined. As the field moves forward, a cautiously optimistic outlook can be expected, focusing on comprehensive data from phase III trials to define the role of FXI inhibitors in various clinical scenarios.

Anesthetic Implications of Factor XI Deficiency: A Clinical Case Study and Review of Literature

Factor XI deficiency, a rare but significant coagulopathy, poses unique challenges in perioperative management, particularly in obstetric settings. This review provides an in-depth exploration of the pathophysiology, diagnosis, and anesthetic implications of factor XI deficiency, thereby emphasizing the useful role of anesthesiologists. The variable bleeding phenotype of the disorder necessitates a nuanced understanding and tailored management strategies to mitigate severe perioperative bleeding risks. Conventional coagulation tests, while useful, often fall short in predicting bleeding risks, underscoring the importance of advanced diagnostic tools, such as viscoelastic testing. Viscoelastic testing provides real-time data on clot stability, which allows for immediate intervention and more targeted therapeutic strategies compared to standard coagulation tests. A clinical case of a 25-year-old patient with factor XI deficiency undergoing emergency surgery for an ectopic pregnancy illustrates the application of viscoelastic testing in managing acute bleeding and optimizing patient outcomes and advocates for the development of standardized protocols, continuous monitoring techniques, and enhanced training programs to improve the perioperative care of patients with factor XI deficiency, providing anesthesiologists with the tools necessary to navigate the complexities of factor XI deficiency in the perioperative environment. Integrating these advanced diagnostic and therapeutic approaches could significantly improve patient safety and surgical outcomes in patients with complex coagulopathy.

Laboratory Evaluation of Interferences Associated with Factor XIa Inhibitors Asundexian and Milvexian in Routine Coagulation Assays

Direct oral anticoagulants (DOACs) are increasingly used for the treatment of thrombosis. While inhibitors of factor IIa and factor Xa have shown effectiveness, the risk of bleeding remains a significant concern. Recently, direct factor XIa inhibitors-including asundexian and milvexian-have emerged as potential anticoagulation therapies, based on clinical observations that patients with factor XIa deficiencies seldom present with spontaneous bleeding tendencies. The interferences associated with DOACs in routine and specialised coagulation assays are well-described; however, the interferences associated with emerging FXIa inhibitors are largely uncharacterised. Here, we briefly report the impact of asundexian and milvexian in routine coagulation assays using in vitro plasma-based systems. Asundexian and milvexian induce concentration-dependent prolongations in APTT-based assays with curvilinear regressions, which may be suitable for the measurement of pharmacodynamic effects at peak levels ex vivo. We also report differential sensitivities of APTT-based assays-particularly at higher FXIa inhibitor concentrations-highlighting the clinical need for an extensive evaluation of interferences associated with FXIa inhibitors in coagulation assays.

Real world management of individuals with severe FXI deficiency and its impact on clinical outcomes: Experience from a haemophilia treatment centre

INTRODUCTION

The management of Factor XI deficiency is challenged by a variable association between FXI level and bleeding phenotype. Additionally, there is scarce data describing management strategies and their outcomes, specifically bleeding, thrombosis, and other complications.

AIMS

To evaluate bleeding, thrombosis, and other complications in individuals with severe FXI deficiency seen in our comprehensive haemophilia treatment centre (HTC). Peri-procedural management strategies and the resulting impact on bleeding and other clinically relevant outcomes were reported.

METHODS

Retrospective review of the electronic medical record of adult patients with severe FXI deficiency (< 20% activity) seen at a New York City comprehensive HTC between 2017 and 2022. Procedures, haemostatic management, and outcomes were collected and analysed.

RESULTS

We identified 38 individuals (64%) females with severe FXI deficiency. The mean age was 56 ± 21 years (SD). The median FXI activity level was 3% (IQR: 1-8%). The mean BAT score was 3.1 ± 2.4; (52%) individuals did not have a history of bleeding. A total of 256 surgeries and procedures were performed. There was reduced bleeding with preventative or reactive treatment during procedures. Arterial but not venous thrombotic complications were observed. Plasma was mostly used for procedures associated with higher risk of bleeding and antifibrinolytics for procedures at sites of high fibrinolysis.

CONCLUSIONS

Current management strategies pose a burden of care for these patients and manifested as nonbleeding adverse events and changes in clinical management. These findings highlight the need for novel investigation in predicting and managing bleeding for individuals with severe FXI deficiency.

Rare inherited coagulation disorders: no longer orphan and neglected

Rare inherited coagulation disorders due to the deficiency or dysfunction of coagulation factors have until recently received less clinical attention than hemophilias and von Willebrand disease. This situation has changed in the last decades, mainly due to therapeutic progress with the availability of more and safer products for replacement therapy produced by plasma fractionation or recombinant DNA technology. This narrative review, based on the latest literature and expert opinion, emphasizes the progress achieved for each of the rare deficiencies, mentions the still unmet therapeutic needs, and sketches the perspectives for further progress.

Targeting factor XI and factor XIa to prevent thrombosis

ABSTRACT

Direct oral anticoagulants (DOACs) that inhibit the coagulation proteases thrombin or factor Xa (FXa) have replaced warfarin and other vitamin K antagonists (VKAs) for most indications requiring long-term anticoagulation. In many clinical situations, DOACs are as effective as VKAs, cause less bleeding, and do not require laboratory monitoring. However, because DOACs target proteases that are required for hemostasis, their use increases the risk of serious bleeding. Concerns over therapy-related bleeding undoubtedly contribute to undertreatment of many patients who would benefit from anticoagulation therapy. There is considerable interest in the plasma zymogen factor XI (FXI) and its protease form factor XIa (FXIa) as drug targets for treating and preventing thrombosis. Laboratory and epidemiologic studies support the conclusion that FXI contributes to venous and arterial thrombosis. Based on 70 years of clinical observations of patients lacking FXI, it is anticipated that drugs targeting this protein will cause less severe bleeding than warfarin or DOACs. In phase 2 studies, drugs that inhibit FXI or FXIa prevent venous thromboembolism after total knee arthroplasty as well as, or better than, low molecular weight heparin. Patients with heart disease on FXI or FXIa inhibitors experienced less bleeding than patients taking DOACs. Based on these early results, phase 3 trials have been initiated that compare drugs targeting FXI and FXIa to standard treatments or placebo. Here, we review the contributions of FXI to normal and abnormal coagulation and discuss results from preclinical, nonclinical, and clinical studies of FXI and FXIa inhibitors.