Why factor XI deficiency is a clinical concern

The spectrum of factor XI deficiency in Southeast China: four recurrent variants can explain most of the deficiencies

BACKGROUND

Factor XI (FXI) deficiency is an autosomal hemorrhagic disorder characterized by reduced plasma FXI levels. Multiple ancestral variants in the F11 gene have been identified in Ashkenazi Jews and other selected European populations. However, there are few reports of predominant variants in Chinese and/or East Asian populations. The aim of this study is to characterize the genotypes and phenotypes of FXI deficiency and identify the predominant variants.

RESULTS

Of the 41 FXI-deficient patients, 39 exhibited severe FXI defects, considerably more than those with partial defects. The APTT levels showed a negative correlation with FXI activity levels (coefficient=-0.584, P < .001). Only nine patients experienced mild bleeding, including one partially defective patient and eight severely defective patients. The majority of patients were referred for preoperative screenings (n = 22) and checkups (n = 14). Genetic analysis revealed that 90% of the patients had genetic defects, with 2, 16, and 19 cases of heterozygous, homozygous, and compound heterozygous patients, respectively. Seventeen variants were detected in the F11 gene (6 novel), including eleven missense variants, four nonsense variants, and two small deletions scattered throughout the F11. Of the 11 missense variants, six have not yet been studied for in vitro expression. Protein modeling analyses indicated that all of these variants disrupted local structural stability by altering side-chain orientation and hydrogen bonds. Nine variants, consisting of three missense and six null variants, were detected with a frequency of two or more. The highest allele frequency was observed in p.Q281* (21.25%), p.W246* (17.50%), p.Y369* (12.50%), and p.L442Cfs*8 (12.50%). The former two were variants specific to East Asia, while the remaining two were southeast China-specific variants.

CONCLUSION

Our population-based cohort demonstrated that no correlation between the level of FXI activity and the bleeding severity in FXI deficiency. Additionally, the prevalence of FXI deficiency may have been underestimated. The nonsense p.Q281* was the most common variant in southeast China, suggesting a possible founder effect.

Factor XI and coagulation. Factor XI inhibitors - antithrombotic perspectives

Factor XI is a zymogen with an important role in the coagulation cascade. It is activated by FXII, thrombin and or it can be autoactivated. It has a prothrombotic effect after being activated by thrombin, but also through its antifibrinolytic action, stabilizing the formed clot. Hereditary deficiency of FXI causes haemophilia C - a disease manifested by an usually provoked, small to moderate mucosal bleeding. People with severe FXI deficiency have a low risk of thrombotic events. Conversely, increased FXI values have been found to be associated with increased risk of venous thromboembolism and ischemic stroke. Lowering serum FXI levels has become a treatment target for the prevention of thrombotic events. New pharmacological agents - FXI inhibitors - have been investigated in phase II clinical trials, with promising results in terms of efficacy and safety in the prevention of thrombotic events. FXI inhibitors are emerging as new anticoagulant agents with broad indication prospects beyond direct oral anticoagulants and vitamin K antagonists.

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.

Management of severe factor XI deficiency in pregnancy: A case report

Factor XI (FXI) deficiency is one of the rarest coagulation disorders with a frequency of 1:1,000,000. A 30-year-old woman, diagnosed with FXI deficiency at the age of 4, was admitted to our maternity service at 25 weeks of gestation. The patient had no history of hemorrhage or abnormal bleeding, and the clinical examination was unremarkable. Antenatal care was also normal. The parturient was admitted in early labor at 38 weeks of gestation. Despite the absence of clinical hemorrhagic syndrome, a transfusion of fresh frozen plasma combined with tranexamic acid was initiated once the active stage of labor was started. Management of FXI deficiency in pregnant women is a challenge due to its unpredictable bleeding tendency, and careful planning and knowledge of appropriate hemostatic management is pivotal for their care.

One case of surgical treatment of coagulation factor XI deficiency complicated with esophageal cancer: a case report

BACKGROUND

Coagulation factor XI deficiency is an autosomal recessive hereditary disease with a low incidence. It usually occurs after surgery or trauma; Esophageal cancer is a common malignant tumor of the digestive tract in China. But so far, surgery-based comprehensive treatment of esophageal cancer still dominates.

CASE PRESENTATION

We report a case of an Asian patient with XI factor deficiency and lower esophageal squamous cell carcinoma who was admitted to our hospital recently. After active preoperative preparation, the operation was successfully performed, and there was no obvious abnormal bleeding during and after the operation.

CONCLUSIONS

Coagulation factor XI deficiency is a relatively rare disease, and patients with the disease will face a greater risk of bleeding during the perioperative period. The encouraging perioperative outcome enables us to have a deeper understanding of surgical treatment strategies for patients with Coagulation factor XI deficiency.

Anticoagulation in chronic kidney disease: current status and future perspectives

Chronic kidney disease (CKD) is being diagnosed increasingly worldwide. It is often identified in individuals with comorbidities, which may increase the already heightened risk of thrombosis and hemorrhage associated with CKD. Oral anticoagulation is an effective means of reducing rates of ischemic stroke and systemic embolism in patients with atrial fibrillation and minimizes the morbidity and mortality caused by venous thromboembolic disease. Despite the proven benefits in the majority of patients, these have not been so clearly realized in patients with CKD due to the precarious balance between bleeding and thromboembolic complications. In this review, the current status of anticoagulant utilization in CKD is examined, and some practical recommendations are put forward to assist in the decision-making process of safely anticoagulating patients with CKD diagnosed with atrial fibrillation and venous thromboembolism.

Factor XI Inhibition for the Prevention of Catheter-Associated Thrombosis in Patients With Cancer Undergoing Central Line Placement: A Phase 2 Clinical Trial

BACKGROUND

Despite the ubiquitous utilization of central venous catheters in clinical practice, their use commonly provokes thromboembolism. No prophylactic strategy has shown sufficient efficacy to justify routine use. Coagulation factors FXI (factor XI) and FXII (factor XII) represent novel targets for device-associated thrombosis, which may mitigate bleeding risk. Our objective was to evaluate the safety and efficacy of an anti-FXI mAb (monoclonal antibody), gruticibart (AB023), in a prospective, single-arm study of patients with cancer receiving central line placement.

METHODS

We enrolled ambulatory cancer patients undergoing central line placement to receive a single dose of gruticibart (2 mg/kg) administered through the venous catheter within 24 hours of placement and a follow-up surveillance ultrasound at day 14 for evaluation of catheter thrombosis. A parallel, noninterventional study was used as a comparator.

RESULTS

In total, 22 subjects (n=11 per study) were enrolled. The overall incidence of catheter-associated thrombosis was 12.5% in the interventional study and 40.0% in the control study. The anti-FXI mAb, gruticibart, significantly prolonged the activated partial thromboplastin time in all subjects on day 14 compared with baseline (P<0.001). Gruticibart was well tolerated and without infusion reactions, drug-related adverse events, or clinically relevant bleeding. Platelet flow cytometry demonstrated no difference in platelet activation following administration of gruticibart. T (thrombin)-AT (antithrombin) and activated FXI-AT complexes increased following central line placement in the control study, which was not demonstrated in our intervention study. CRP (C-reactive protein) did not significantly increase on day 14 in those who received gruticibart, but it did significantly increase in the noninterventional study.

CONCLUSIONS

FXI inhibition with gruticibart was well tolerated without any significant adverse or bleeding-related events and resulted in a lower incidence of catheter-associated thrombosis on surveillance ultrasound compared with the published literature and our internal control study. These findings suggest that targeting FXI could represent a safe intervention to prevent catheter thrombosis.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04465760.

Factor activity levels and bleeding scores in pediatric hemophilia carriers enrolled in the ATHNdataset

BACKGROUND

Multiple studies have now shown that a significant proportion of hemophilia carriers meet the criteria for having hemophilia and/or report abnormal bleeding. However, to date, investigations of hemophilia carriers have almost exclusively involved women over 18 years of age. Little is known about factor activity levels and bleeding scores in carriers during childhood. We queried a large deidentified database of subjects with bleeding disorders residing in the United States to determine factor activity levels and bleeding scores.

PROCEDURES

The ATHNdataset was queried for hemophilia carriers under 18 years of age. Collected information included demographics, factor activity levels, and bleeding scores.

RESULTS

Over 700 carriers in the pediatric age group were identified, of which 626 submitted factor activity levels. Nearly half had factor activity levels less than 40 IU/dL, thereby meeting criteria for having hemophilia. Of those reporting bleeding scores, only 13.5% reported an abnormal bleeding score for age. The proportion reporting abnormal bleeding scores was higher in those with factor levels less than 40 IU/dL (23%) than those greater than 40 IU/dL (9.7%).

CONCLUSIONS

The proportion of pediatric carriers with hemophilia was double of that previously reported for adults. Of those with hemophilia reporting a bleeding score, the majority (77%) did not report an abnormal bleeding score for age. However, nearly 10% of pediatric carriers not meeting criteria for having hemophilia reported abnormal bleeding scores for age. Similar results are reported in adults suggesting that factor activity levels may not be predictive of bleeding symptoms in carriers.

Congenital factor XI deficiency with multiple tooth extractions (Case report)

Congenital factor XI deficiency (CFXI) is a rare blood disorder that occurs in one of every one million individuals. Given its rarity, there are very few reports of surgical procedures performed in the oral region CFXI patients. The present study reports the case of a 43-year-old man with CFXI who experienced multiple tooth extractions. It also conducted a review of the literature and treatment outline. We preoperatively administered fresh frozen plasma (FFP) before the tooth extraction and continued to transfuse FFP at the rate of 2 units per day from day 1 to 4 of admission. The extractions were divided into two parts, maxillary and mandibular and the teeth extracted on days 2 and 4 of admission. The patient was discharged on day 6 of admission because there was good progress and no postoperative bleeding. Therefore, it was possible to perform multiple tooth extractions without abnormal bleeding in the oral cavity; the chance of bleeding was reduced by administering FFP and increasing local hemostasis in CFXI patients.

A new strategy for anticoagulation: The factor XI inhibitors

Direct oral anticoagulants (DOACs) are currently the first-choice therapy for the prevention of cardioembolic events in patients with atrial fibrillation and for the treatment of venous thromboembolism (VTE) due to their more favorable efficacy to safety profile in comparison to vitamin K antagonists (VKA). DOACs did not show a clinical benefit when used for in stroke prevention in patients with mechanic or rheumatic valves or in those who underwent transcatheter aortic valve implantation (TAVI), in the treatment of VTE in patients with antiphospholipid antibody syndrome and in prevention of VTE in medically ill patients. There are some concerns for bleeding excess at the gastrointestinal site for some, but not all, DOACs. In recent years, in order to overcome the limitations of the available DOACs and to explore the advantages of anticoagulation in additional clinical settings, the development of factor XI and factor XII inhibitors as anticoagulant agents has been proposed. Emerging data show that factor XI has a minor role in the physiological process of hemostasis and an important role in the development of thrombosis. Bleeding has been viewed for several years as an unavoidable side effect of anticoagulant therapy. The aim of factor XI inhibitors is to challenge this dogma by favoring the uncoupling between hemostasis and thrombosis. This paper provides an update on the rationale for the use of factor XI inhibitors, their pharmacological properties and the preliminary clinical findings.

Abelacimab in Cancer-Associated Thrombosis: The Right Drug at the Right Time for the Right Purpose. A Comprehensive Review

Cancer-associated thrombosis (CAT) is a devastating complication of cancer that can significantly impact a patient's health and life. The incidence of CAT is approximately 20%, and 1 in 5 cancer patients will develop CAT annually. Indeed, CAT can promote pulmonary embolism and deep vein thrombosis, leading to increased morbidity and mortality that dramatically impact survival. CAT can also provoke delay or discontinuation of anticancer treatment, which may result in a lack of treatment efficacy and high costs for patients, institutions, and society. Current guidelines advocate direct oral anticoagulants (DOACs) as the first-line anticoagulant option in CAT. Compared to low-molecular-weight-heparins (LMWHs), DOACs are advantageous in that they typically have an oral route of administration, do not require laboratory monitoring, and have a more predictable anticoagulant effect. However, in patients with thrombocytopenia, renal failure, or those receiving anticancer regimens with potential for drug-drug interactions, LMWH is still the mainstay of care. The main limitation of current anticoagulant agents is related to bleeding risk (BR), both for DOACs and LMWHs. Specifically, DOACs have been associated with high BR in gastrointestinal and genitourinary cancers. In this challenging scenario, abelacimab, an anti-factor XI agent, could represent a viable option in the management of CAT due to its "hemostasis sparing" effect. The safe profile of abelacimab could be useful in patients with active malignancy and CAT, as long-term anticoagulant therapy is often required. Two ongoing international phase III trials (Aster and Magnolia) compare abelacimab with the standard of care (i.e., apixaban in patients with CAT and dalteparin in those with CAT and high BR, respectively). Abelacimab is a new and attractive anticoagulant for the management of CAT, especially in the insidious and critical scenario of active cancer patients with venous thromboembolism and high BR. The aim of this narrative review is to discuss the updated evidence on the performance of DOACs and LMWHs in the treatment of CAT and to focus on the potential role of abelacimab in CAT and its promising associated clinical trials.

Determination of the Potential Clinical Benefits of Small Molecule Factor XIa Inhibitors in Arterial Thrombosis

Anticoagulants are the mainstay for the prevention and treatment of thrombosis. However, bleeding complications remain a primary concern. Recent advances in understanding the contribution of activated factor XI (FXIa) in arterial thrombosis with a limited impact on hemostasis have led to the development of several FXIa-targeting modalities. Injectable agents including monoclonal antibodies and antisense oligonucleotides against FXIa have been primarily studied in venous thrombosis. The orally active small molecules that specifically inhibit the active site of FXIa are currently being investigated for their antithrombotic activity in both arteries and veins. This review focuses on a discussion of the potential clinical benefits of small molecule FXIa inhibitors, mainly asundexian and milvexian, in arterial thrombosis based on their pharmacological profiles and the compelling results of phase 2 clinical studies. The preclinical and epidemiological basis for the impact of FXIa in hemostasis and arterial thrombosis is also addressed. In recent clinical study results, asundexian appears to reduce ischemic events in patients with myocardial infarction and minor-to-moderate stroke, whereas milvexian possibly provides benefits in patients with minor stroke or high-risk transient ischemic attack (TIA). In addition, asundexian and milvexian had a minor impact on hemostasis even in combination with dual-antiplatelet therapy. Other orally active FXIa inhibitors also produce antithrombotic activity in vivo with low bleeding risk. Therefore, FXIa inhibitors might represent a new class of direct-acting oral anticoagulants (DOACs) for the treatment of thrombosis, although the explicit clinical positions of asundexian and milvexian in patients with ischemic stroke, high-risk TIA, and coronary artery disease require confirmation from the outcomes of ongoing phase 3 trials.

Impact of genetic structural variants in factor XI deficiency: identification, accurate characterization, and inferred mechanism by long-read sequencing

BACKGROUND

Congenital factor XI (FXI) deficiency is a probably underestimated coagulopathy that confers antithrombotic protection. Characterization of genetic defects in F11 is mainly focused on the identification of single-nucleotide variants and small insertion/deletions because they represent up to 99% of the alterations accounting for factor deficiency, with only 3 gross gene defects of structural variants (SVs) having been described.

OBJECTIVES

To identify and characterize the SVs affecting F11.

METHODS

The study was performed in 93 unrelated subjects with FXI deficiency recruited in Spanish hospitals over a period of 25 years (1997-2022). F11 was analyzed by next-generation sequencing, multiplex ligand probe amplification, and long-read sequencing.

RESULTS

Our study identified 30 different genetic variants. Interestingly, we found 3 SVs, all heterozygous: a complex duplication affecting exons 8 and 9, a tandem duplication of exon 14, and a large deletion affecting the whole gene. Nucleotide resolution obtained by long-read sequencing revealed Alu repetitive elements involved in all breakpoints. The large deletion was probably generated de novo in the paternal allele during gametogenesis, and despite affecting 30 additional genes, no syndromic features were described.

CONCLUSION

SVs may account for a high proportion of F11 genetic defects implicated in the molecular pathology of congenital FXI deficiency. These SVs, likely caused by a nonallelic homologous recombination involving repetitive elements, are heterogeneous in both type and length and may be de novo. These data support the inclusion of methods to detect SVs in this disorder, with long-read-based methods being the most appropriate because they detect all SVs and achieve adequate nucleotide resolution.

Targeting the contact system in a rabbit model of extracorporeal membrane oxygenation

Previous studies suggested that contact pathway factors drive thrombosis in mechanical circulation. We used a rabbit model of veno-arterial extracorporeal circulation (VA-ECMO) to evaluate the role of factors XI and XII in ECMO-associated thrombosis and organ damage. Factors XI and XII (FXI, FXII) were depleted using established antisense oligonucleotides before placement on a blood-primed VA-ECMO circuit. Decreasing FXII or FXI to < 5% of baseline activity significantly prolonged ECMO circuit lifespan, limited the development of coagulopathy, and prevented fibrinogen consumption. Histological analysis suggested that FXII depletion mitigated interstitial pulmonary edema and hemorrhage whereas heparin and FXI depletion did not. Neither FXI nor FXII depletion was associated with significant hemorrhage in other organs. In vitro analysis showed that membrane oxygenator fibers (MOFs) alone are capable of driving significant thrombin generation in a FXII- and FXI-dependent manner. MOFs also augment thrombin generation triggered by low (1 pM) or high (5 pM) tissue factor concentrations. However, only FXI elimination completely prevented the increase in thrombin generation driven by MOFs, suggesting MOFs augment thrombin-mediated FXI activation. Together, these results suggest that therapies targeting FXII or FXI limit thromboembolic complications associated with ECMO. Further studies are needed to determine the contexts wherein targeting FXI and FXII, either alone or in combination, would be most beneficial in ECMO. Moreover, studies are also needed to determine the potential mechanisms coupling FXII to end-organ damage in ECMO.

Perioperative Management of a Patient with Hemophilia C and Allergy to Fresh Frozen Plasma

Hemophilia C is a rare bleeding disorder characterized by a deficiency in clotting factor XI (fXI) and has no standard of care for preoperative optimization before cardiac surgery. Normalization of fXI levels in patients with hemophilia C can be achieved with fresh frozen plasma (FFP), which sometimes results in allergic reactions. We present a case of a patient with hemophilia C requiring coronary artery bypass grafting surgery who developed an allergic reaction to FFP. Our report underscores the balance between thrombosis and bleeding risks when devising a perioperative plan for patients with hemophilia C.

How to Deal With Hemophilia C in Endoscopic Urologic Surgery: Lessons Learned From a Transurethral Resection of Bladder Tumor Case

Factor XI deficiency (hemophilia C or Rosenthal syndrome) is an inherited rare disorder that leads to abnormal bleeding due to the paucity of the protein named factor XI, which plays a role in the blood clotting cascade. A 42-year-old male was referred to the urology outpatient clinic with macroscopic hematuria. The patient was scheduled for a repeat transurethral resection of a bladder tumor (TURBT). Preoperative coagulation parameters were as follows: the international normalized ratio (INR) was 0.95 (0.85-1.2), the prothrombin time was 10.9 seconds (10-15), and the partial thromboplastin time was 43.7 seconds (21-36). On the second postoperative day, he developed pelvic pain and discomfort. An abdominal CT revealed a 10 cm mass consistent with clot retention. The patient received two units of erythrocyte suspension and six units of fresh frozen plasma to prevent the depletion of hemoglobin and control urinary bleeding. The patient was discharged with a good recovery from the hospital three days after the second surgery. Hematologic disorders are rare but might have fatal consequences following surgery if unnoticed at the earliest stage. Clinicians must consider that patients with a history of unusual bleeding or borderline coagulation parameters might have an underlying hematological disorder and perform a further evaluation.

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.

Coming soon to a pharmacy near you? FXI and FXII inhibitors to prevent or treat thromboembolism

Anticoagulants have been in use for nearly a century for the treatment and prevention of venous and arterial thromboembolic disorders. The most dreaded complication of anticoagulant treatment is the occurrence of bleeding, which may be serious and even life-threatening. All available anticoagulants, which target either multiple coagulation factors or individual components of the tissue factor (TF) factor VIIa or the common pathways, have the potential to affect hemostasis and thus to increase bleeding risk in treated patients. While direct oral anticoagulants introduced an improvement in care for eligible patients in terms of safety, efficacy, and convenience of treatment, there remain unmet clinical needs for patients requiring anticoagulant drugs. Anticoagulant therapy is sometimes avoided for fear of hemorrhagic complications, and other patients are undertreated due to comorbidities and the perception of increased bleeding risk. Evidence suggests that the contact pathway of coagulation has a limited role in initiating physiologic in vivo coagulation and that it contributes to thrombosis more than it does to hemostasis. Because inhibition of the contact pathway is less likely to promote bleeding, it is an attractive target for the development of anticoagulants with improved safety. Preclinical and early clinical data indicate that novel agents that selectively target factor XI or factor XII can reduce venous and arterial thrombosis without an increase in bleeding complications.

Assessment of quality of life by functional independence score in hemophilic patients: a single-center experience

Background

Hemophilia is an inherited condition that is caused by the deficiency of clotting factors in the blood. The most common presentations of hemophilia are hemarthrosis and muscle hemorrhage. The severity of the bleeding episodes can vary from mild to severe resulting in pain and swelling of the joints and the muscles. Repeated musculoskeletal bleeding can result in hemophilic arthropathies with subsequent joint degeneration and deformity. Our study aims to clinically assess the quality of life in hemophilic patients in terms of disease severity and morbidity in our community using the Functional Independence Score for Hemophilia (FISH).

Results

Our cross-sectional study which involved 64 hemophilia patients revealed that the most affected joints were the weight-bearing large joints (knees, elbows, ankles) and this was associated with a lower FISH score. While the total FISH score showed a significant positive correlation with the factor activity level, the average FISH score was 21.11 ± 4.5, and the score was slightly lower in severe hemophilia compared to mild-moderate disease.

Conclusion

We concluded that there is a significant decline in the functional ability of hemophilia patients having disease affecting the knee and elbow joints. Moreover, squatting was significantly reduced in patients with severe hemophilia. The quality of patients’ life can be improved by early and regular physiotherapy and regular administration of the prophylactic factor.

Blood plasma proteome alteration after local tissue damage induced by Bothrops erythromelas snake venom in mice

Snakes of the genus Bothrops are responsible the most snakebites in the Brazil, causing a diverse and complex pathophysiological condition. Bothrops erythromelas is the main specie of medical relevance found in the Caatinga from the Brazilian Northeast region. The pathophysiological effects involving B. erythromelas snakebite as well as the organism reaction in response to this envenomation are not so explored. Thus, edema was induced in mice paws using 2.5 μg or 5.0 μg of B. erythromelas venom, and the percentage of edema was measured. Plasma was collected 30  minutes after the envenomation-induced in mice and analyzed by mass spectrometry. It was identified a total of 112 common plasma proteins differentially abundant among experimental groups, which are involved with the complement system and coagulation cascades, oxidative stress, neutrophil degranulation, platelets degranulation and inflammatory response. Apolipoprotein A1 (Apoa), serum amyloid protein A-4 (Saa4), adiponectin (Adipoq) showed up-regulated in mice plasma after injection of venom, while fibulin (Fbln1), factor XII (F12) and vitamin K-dependent protein Z (Proz) showed down-regulated. The results indicate a protein pattern of thrombo-inflammation to the B. erythromelas snakebite, evidencing potential biomarkers for monitoring this snakebite, new therapeutic targets and its correlations with the degree of envenomation once showed modulations in the abundance among the different groups according to the amount of venom injected into the mice.

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.

Case of concurrent factor VII and factor XI deficiencies manifesting as spontaneous lower extremity compartment syndrome

Factor VII and XI deficiencies are rare bleeding disorders typically associated with mild or provoked bleeding. This case report describes a patient with factor VII and XI deficiencies with an unprovoked episode of lower extremity hematoma causing compartment syndrome requiring multiple surgeries, extensive transfusion of blood products, and ultimately amputation.

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.

Skeletal muscle myosin promotes coagulation by binding factor XI via its A3 domain and enhancing thrombin-induced factor XI activation

Skeletal muscle myosin (SkM) has been shown to possess procoagulant activity; however, the mechanisms of this coagulation-enhancing activity involving plasma coagulation pathways and factors are incompletely understood. Here, we discovered direct interactions between immobilized SkM and coagulation factor XI (FXI) using biolayer interferometry (K_d = 0.2 nM). In contrast, we show that prekallikrein, a FXI homolog, did not bind to SkM, reflecting the specificity of SkM for FXI binding. We also found that the anti-FXI monoclonal antibody, mAb 1A6, which recognizes the Apple (A) 3 domain of FXI, potently inhibited binding of FXI to immobilized SkM, implying that SkM binds FXI A3 domain. In addition, we show that SkM enhanced FXI activation by thrombin in a concentration-dependent manner. We further used recombinant FXI chimeric proteins in which each of the four A domains of the heavy chain (designated A1 through A4) was individually replaced with the corresponding A domain from prekallikrein to investigate SkM-mediated enhancement of thrombin-induced FXI activation. These results indicated that activation of two FXI chimeras with substitutions of either the A3 domains or A4 domains was not enhanced by SkM, whereas substitution of the A2 domain did not reduce the thrombin-induced activation compared with wildtype FXI. These data strongly suggest that functional interaction sites on FXI for SkM involve the A3 and A4 domains. Thus, this study is the first to reveal and support the novel intrinsic blood coagulation pathway concept that the procoagulant mechanisms of SkM include FXI binding and enhancement of FXI activation by thrombin.

Intraoperative thromboelastography-guided transfusion in a patient with factor XI deficiency: A case report

BACKGROUND

Factor XI (FXI) deficiency, also known as hemophilia C, is a rare bleeding disorder of unpredictable severity that correlates poorly with FXI coagulation activity. This often poses great challenges in perioperative hemostatic management. Thromboelastography (TEG) is a method for testing blood coagulation using a viscoelastic hemostatic assay of whole blood to assess the overall coagulation status. Here, we present the successful application of intraoperative TEG monitoring in an FXI-deficient patient as an individualized blood transfusion strategy.

CASE SUMMARY

A 21-year-old male patient with FXI deficiency was scheduled to undergo reconstructive surgery for macrodactyly of the left foot under general anesthesia. To minimize his bleeding risk, he was scheduled to receive fresh frozen plasma (FFP) as an empirical prophylactic FXI replacement at a dose of 15-20 mL/kg body weight (900-1200 mL) before surgery. Subsequent FFP transfusion was to be adjusted according to surgical need. Instead, TEG assessment was used at the beginning and toward the end of his surgery. According to intraoperative TEG results, the normalization of coagulation function was achieved with an infusion of only 800 mL FFP, and blood loss was minimal. The patient showed an uneventful postoperative course and was discharged on postoperative day 8.

CONCLUSION

TEG can be readily applied in the intraoperative period to individualize transfusion needs in patients with rare inherited coagulopathy.

Genetic analysis of compound heterozygous pathogenic variants of the F11 gene in two Chinese patients with hereditary factor XI deficiency

The aim of this study was to explore the molecular pathogenesis of two families with compound heterozygous hereditary factor XI deficiency. All the exons, flanking sequences, 5' and 3' untranslated regions of the F11 gene were analysed by direct DNA sequencing. The suspected variants were confirmed by reverse sequencing. Bioinformatics softwares were used to analysis the conservation and the possible impact of these pathogenic variants. Genetic analysis revealed c.689G > T and c.1556G > A variants of F11 gene in family A; c.1107C > A and c.1557G > C variants of F11 gene in family B. These variants sites were highly conserved among homologous species. Bioinformatics and structural analysis demonstrated these variants were pathogenic and could affect the protein structure. The c.689G > T, c.1556G > A, c.1107C > A and the c.1557G > C heterozygous variants might be responsible for the decrease of FXI levels in probands. In addition, c.689G > T (NM_000128.4) is a novel pathogenic variant site, which has not been reported.

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.

Factor XI deficiency: About 20 cases and literature review

INTRODUCTION

Factor XI deficiency is a rare coagulation disorder with variable bleeding manifestations.

AIM

To evaluate the correlation between the degree of factorXI deficiency and the clinical expression of the disease.

METHODS

Retrospective study, spanning 10 years from January 1, 2010 to December 31, 2019, concerning patients followed at the Hemophilia Center at Aziza Othmana Hospital in Tunis. The data were collected from the medical records. The determination of PT, APTT, fibrinogen level and coagulation factors are performed by coagulometric technique on STA® compact / ACL TOP®. FactorXI deficiency was confirmed on two different samples. Statistical analysis of the clinical-biological correlation was performed using the chi-square test. The significance level was 0.05.

RESULTS

Twenty patients were collected. The mean age of discovery was 25 years with a sex ratio (M/F) =0.33. The circumstances of discovery were incidental in 14 patients. A family history of bleeding was reported in 30% of cases. Eight patients underwent surgery, six of whom had a simple postoperative course. The APTT was prolonged and isolated in 75% of cases. The hemostasis test was normal in 5 cases. The average FactorXI level was 24%. The tendency to bleed did not seem to be correlated with FactorXI levels.

CONCLUSION

Prospective multicenter studies including molecular study would be necessary to better elucidate this rare disorder.

A proposal for managing bleeding in patients on therapeutic factor XI(a) inhibitors

Several drugs that reduce functional levels of the plasma protease zymogen factor XI (FXI), or that inhibit its activated form (FXIa), are being evaluated as treatments to prevent thrombosis. Based on the observation that individuals with inherited FXI deficiency have a relatively mild bleeding disorder, it is anticipated that therapeutic FXI(a) inhibitors will have a smaller impact on hemostasis than anticoagulants targeting thrombin or factor Xa. However, even if FXI(a) inhibitors are determined to be safer than currently used anticoagulants, some patients on these drugs will experience abnormal bleeding or require emergent surgery. Strategies for dealing with such situations are required. Treatment with antifibrinolytic agents and low doses of recombinant factor VIIa effectively prevent abnormal bleeding in FXI-deficient patients with alloantibody inhibitors to FXI who undergo surgery. We propose that a similar strategy can be used for patients on therapeutic FXI(a) inhibitors who are bleeding or require invasive procedures.

Phenotype and genotype analysis of patients with severe factor XI deficiency in Shaanxi Province, China

Congenital coagulation factor XI (FXI) deficiency is a rare bleeding disorder with a heterogeneous haemorrhagic phenotype and various hotspot gene mutations associated with race and geography. Studies on FXI deficiency in Shaanxi Province, China, are scarce. In this study, seven patients with severe FXI deficiency and several family members were analysed. The International Society on Thrombosis and Hemostasis-Bleeding Assessment Tool (ISTH-BAT) was applied to assess bleeding symptoms. FXI activity was determined using a one-stage method, and the FXI antigen was measured by enzyme-linked immunosorbent assay. Targeted capture next-generation sequencing and Sanger sequencing were applied to detect FXI gene mutations. The bleeding phenotype varied, although none of the participants had a history of spontaneous bleeding. One maternal received replacement therapy during the perinatal period, one female patient presented with menorrhagia, one male patient experienced severe postoperative bleeding and others were asymptomatic. Family members with heterozygous mutations were all asymptomatic. The FXI activity of all the patients ranged from less than 1 to 3.1 IU/dl, and a synchronous decrease in the FXI antigen was observed. Two missense mutations (p. Gly350Glu and p. Cys482Trp), one nonsense mutation (p. Gln384∗) and one novel frameshift mutation (p. Ser225Phefs∗16) were detected. The bleeding manifestations and severity of severe FXI deficiency varied and were not related to its activity. Three reported mutations and one novel frameshift mutation were identified, thus extending the mutation spectrum of FXI deficiency.

Analysis of 272 Genetic Variants in the Upgraded Interactive FXI Web Database Reveals New Insights into FXI Deficiency

Coagulation Factor XI (FXI) is a plasma glycoprotein composed of four apple (Ap) domains and a serine protease (SP) domain. FXI circulates as a dimer and activates Factor IX (FIX), promoting thrombin production and preventing excess blood loss. Genetic variants that degrade FXI structure and function often lead to bleeding diatheses, commonly termed FXI deficiency. The first interactive FXI variant database underwent initial development in 2003 at https://www.factorxi.org . Here, based on a much improved FXI crystal structure, the upgraded FXI database contains information regarding 272 FXI variants (including 154 missense variants) found in 657 patients, this being a significant increase from the 183 variants identified in the 2009 update. Type I variants involve the simultaneous reduction of FXI coagulant activity (FXI:C) and FXI antigen levels (FXI:Ag), whereas Type II variants result in decreased FXI:C yet normal FXI:Ag. The database updates now highlight the predominance of Type I variants in FXI. Analysis in terms of a consensus Ap domain revealed the near-uniform distribution of 81 missense variants across the Ap domains. A further 66 missense variants were identified in the SP domain, showing that all regions of the FXI protein were important for function. The variants clarified the critical importance of changes in surface solvent accessibility, as well as those of cysteine residues and the dimer interface. Guidelines are provided below for clinicians who wish to use the database for diagnostic purposes. In conclusion, the updated database provides an easy-to-use web resource on FXI deficiency for clinicians.

Anticoagulation in patients with kidney failure on dialysis: factor XI as a therapeutic target

Chronic kidney disease is present in almost 10% of the world population and is associated with excess mortality and morbidity. Reduced glomerular filtration rate and the presence and extent of proteinuria, key domains of chronic kidney disease, have both been shown to be strong and independent risk factors for cardiovascular disease. Patients with kidney failure requiring dialysis are at highest risk for cardiovascular events (e.g., stroke or myocardial infarction), and of developing chronic cardiovascular conditions, such as heart failure. Despite the high burden of cardiovascular disease, there is a paucity of evidence supporting therapies to reduce this risk. Although long-term anticoagulant treatment has the potential to prevent thromboembolism in persons with kidney failure on dialysis, this possibility remains understudied. The limited data available on anticoagulation in patients with kidney failure has focused on vitamin K antagonists or direct oral anticoagulants that inhibit thrombin or factor (F) Xa. The risk of bleeding is a major concern with these agents. However, FXI is emerging as a potential safer target for new anticoagulants because FXI plays a greater part in thrombosis than in hemostasis. In this article, we (i) explain the rationale for considering anticoagulation therapy in patients with kidney failure to reduce atherothrombotic events, (ii) highlight the limitations of current anticoagulants in this patient population, (iii) explain the potential benefits of FXI inhibitors, and (iv) summarize ongoing studies investigating FXI inhibition in patients with kidney failure on dialysis.

Identification of the factor XII contact activation site enables sensitive coagulation diagnostics

Contact activation refers to the process of surface-induced activation of factor XII (FXII), which initiates blood coagulation and is captured by the activated partial thromboplastin time (aPTT) assay. Here, we show the mechanism and diagnostic implications of FXII contact activation. Screening of recombinant FXII mutants identified a continuous stretch of residues Gln317-Ser339 that was essential for FXII surface binding and activation, thrombin generation and coagulation. Peptides spanning these 23 residues competed with surface-induced FXII activation. Although FXII mutants lacking residues Gln317-Ser339 were susceptible to activation by plasmin and plasma kallikrein, they were ineffective in supporting arterial and venous thrombus formation in mice. Antibodies raised against the Gln317-Ser339 region induced FXII activation and triggered controllable contact activation in solution leading to thrombin generation by the intrinsic pathway of coagulation. The antibody-activated aPTT allows for standardization of particulate aPTT reagents and for sensitive monitoring of coagulation factors VIII, IX, XI.

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.

Mobile Health Technology for the Personalized Therapy of Hemophilia

The management of patients with hemophilia has evolved significantly since the first treatment attempts were made in the late 1930s. Since then, each new step in the treatment of patients with hemophilia has brought important advancements, as well as its unique set of challenges. Today, a patient-centered, individualized comprehensive approach is the new paradigm, moving away from the traditional "one size-fits-all" approach, to provide the best possible care for each patient with a bleeding disorder. As part of this complex task, mobile health applications might have the capacity to play an important role in reaching that goal. However, the use of new electronic technologies as part of a comprehensive treatment approach for patients with hemophilia simultaneously presents a new set of challenges that needs consideration. In the first section, currently available treatment of hemophilia patients will be revised, while in the second part the role of IT software in the treatment monitoring of hemophilia patients will be discussed.

ONO-7684 a novel oral FXIa inhibitor: Safety, tolerability, pharmacokinetics and pharmacodynamics in a first-in-human study

AIMS

The objectives of this study were to investigate the safety, tolerability, pharmacokinetics and pharmacodynamics of single and multiple oral doses of ONO-7684, a novel activated factor XI (FXIa) inhibitor, in healthy subjects.

METHODS

This was a first-in-human (FIH), randomised, placebo-controlled, double-blind, single and multiple dose study in healthy subjects under fed and fasted conditions. This study consisted of two parts: single ascending dose (Part A; 1, 5, 20, 80, 150 or 300 mg ONO-7684 or placebo) and multiple ascending doses (Part B; 80, 150 or 250 mg ONO-7684 or placebo daily for 14 days). In both parts, subjects were randomised in a 3:1 ratio to receive ONO-7684 or placebo.

RESULTS

ONO-7684 was well tolerated at all dose levels tested following both single and repeated doses, with a low overall incidence of treatment-emergent adverse events. There was no evidence to suggest a bleeding risk. Dose proportionality in exposure was observed for the range of 1-300 mg ONO-7684 in Part A. In Part A, the half-life of ONO-7684 administered in the fasted state ranged from 16.0 to 19.8 hours. In Part B, the half-life of ONO-7684 administered in the fed state ranged from 22.1 to 27.9 hours, supporting once daily oral dosing. ONO-7684 strongly inhibited factor XI coagulation activity (FXI:C) and increased activated partial thromboplastin time (aPTT), with a mean maximum on treatment percentage inhibition versus baseline of 92% and a mean maximum on treatment ratio-to-baseline of 2.78, respectively, at 250 mg ONO-7684 daily.

CONCLUSIONS

The data generated in this FIH study demonstrate the promising potential of oral FXIa inhibition and ONO-7684 for indications requiring anticoagulation.

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.

The evolution of factor XI and the kallikrein-kinin system

Factor XI (FXI) is the zymogen of a plasma protease (FXIa) that contributes to hemostasis by activating factor IX (FIX). In the original cascade model of coagulation, FXI is converted to FXIa by factor XIIa (FXIIa), a component, along with prekallikrein and high-molecular-weight kininogen (HK), of the plasma kallikrein-kinin system (KKS). More recent coagulation models emphasize thrombin as a FXI activator, bypassing the need for FXIIa and the KKS. We took an evolutionary approach to better understand the relationship of FXI to the KKS and thrombin generation. BLAST searches were conducted for FXI, FXII, prekallikrein, and HK using genomes for multiple vertebrate species. The analysis shows the KKS appeared in lobe-finned fish, the ancestors of all land vertebrates. FXI arose later from a duplication of the prekallikrein gene early in mammalian evolution. Features of FXI that facilitate efficient FIX activation are present in all living mammals, including primitive egg-laying monotremes, and may represent enhancement of FIX-activating activity inherent in prekallikrein. FXI activation by thrombin is a more recent acquisition, appearing in placental mammals. These findings suggest FXI activation by FXIIa may be more important to hemostasis in primitive mammals than in placental mammals. FXI activation by thrombin places FXI partially under control of the vitamin K-dependent coagulation mechanism, reducing the importance of the KKS in blood coagulation. This would explain why humans with FXI deficiency have a bleeding abnormality, whereas those lacking components of the KKS do not.

Activated Factor XI is Increased in Plasma in Response to Surgical Trauma but not to Recombinant Activated FVII-Induced Thrombin Formation

Aim: Feedback activation of factor XI (FXI) by thrombin is believed to play a critical role in the amplification phase of thrombin generation and to contribute to thrombosis development and hemostasis. However, the activation of FXI by thrombin has been shown in vitro to require a cofactor. In this study, the role of thrombin in activated FXI (FXIa) formation in vivo is investigated.

Methods: The study population comprised probands in whom coagulation activation was triggered by low-dose (15 µg/kg) recombinant activated factor VII (rFVIIa, n =89), of whom 34 with (VTE+) and 45 without a history of venous thromboembolism (VTE−), and patients undergoing major orthopedic surgeries ( n =45). FXIa was quantified via an enzyme capture assay using a monoclonal FXI-specific antibody. Thrombin formation was monitored using an oligonucleotide-based enzyme capture assay and the thrombin activation markers prothrombin fragment 1＋2 (F1＋2) and thrombin–antithrombin complex (TAT).

Results: In the rFVIIa cohort, FXIa and thrombin remained below their lower limit of quantification of 3.48 and 1.06 pmol/L, respectively. By contrast, during the surgeries, median FXIa levels increased from 3.69 pmol/L pre-operatively to 9.41 pmol/L mid-operatively ( P =4·10 ⁻⁴ ) and remained significantly elevated 24 h thereafter, with 9.38 pmol/L ( P =0.001). Peak levels of F1+2 were comparable in the VTE+, VTE−, and surgery cohort (235, 268, and 253 pmol/L), whereas peak TAT levels were higher in the surgery cohort (53.1, 33.9, and 147.6 pmol/L).

Conclusions: Under in vivo conditions, the activation of FXI requires specific local features that are present at the wounded site including potential cofactors of thrombin.

Pharmacological management of rare coagulation factor deficiencies besides hemophilia

INTRODUCTION

Rare coagulation factor deficiencies are less-known disorders with variable effects on the patient's life. Management of such patients is a challenge due to the paucity of evidence-based data, more so when patients with these rare disorders encounter a more rare, related condition, like inhibitor development or thrombosis.

AREA COVERED

A comprehensive literature search related to RCFDs and management was performed in PubMed in order to discuss therapeutic options and challenges, prophylaxis, management of minor and major surgeries, obstetric and gynecological complications, inhibitor development, and thrombosis.

EXPERT OPINION

Although significant changes have occurred in the management of RCFDs in recent years, more evidence-based studies besides expert opinion are needed for optimal management.

A Case Report on an Extremely Rare Disease: Factor XI Deficiency

Factor XI deficiency is a rare condition with an estimated prevalence of about one in one million and is more commonly seen in Ashkenazi Jews (8-9%) due to consanguinity. It occurs because of mutations in the factor XI gene (F11) on chromosome 4(4q35). Patients with this disorder may remain asymptomatic until they undergo any surgical procedure or delivery. The most common sites of bleeding include the oral cavity, pharynx, and genitourinary tract, where there is high fibrinolytic activity. Our patient was asymptomatic his whole life. He never had spontaneous bleeding or bruising; however, he had severe bleeding requiring multiple transfusions of fresh frozen plasma during and after surgeries.

How to Capture the Bleeding Phenotype in FXI-Deficient Patients

Factor XI (FXI) is a serine protease involved in the propagation phase of coagulation and in providing clot stability. Several mutations in the F11 gene lead to FXI deficiency, a rare mild bleeding disorder. Current laboratory methods are unable to assess bleeding risk in FXI-deficient patients, because the degree of bleeding tendency does not correlate with plasma FXI activity as measured by routine coagulometric aPTT–based assays. Bleeding manifestations are highly variable among FXI-deficient patients and FXI replacement therapy can be associated with an increased thrombotic risk. A correct evaluation of the patient hemostatic potential is crucial to prevent under- or overtreatment. In recent years, different research groups have investigated the use of global coagulation assays as alternative for studying the role of FXI in hemostasis and identifying the clinical phenotype of FXI deficiency. This brief review article summarizes the main features of coagulation factor XI and its deficiency and resumes the principle axes of research and methods used to investigate FXI functions.