Factor XI deficiency in Ashkenazi Jews in Israel

Blood clot formation under flow: the importance of factor XI depends strongly on platelet count

A previously validated mathematical model of intravascular platelet deposition and tissue factor (TF)-initiated coagulation under flow is extended and used to assess the influence on thrombin production of the activation of factor XI (fXI) by thrombin and of the activation of factor IX (fIX) by fXIa. It is found that the importance of the thrombin-fXIa-fIXa feedback loop to robust thrombin production depends on the concentration of platelets in the blood near the injury. At a near-wall platelet concentration of ~250,000/μL, typical in vessels in which the shear rate is <200 s(-1), thrombin activation of fXI makes a significant difference only at low densities of exposed TF. If the near-wall platelet concentration is significantly higher than this, either because of a higher systemic platelet count or because of the redistribution of platelets toward the vessel walls at high shear rates, then thrombin activation of fXI makes a major difference even for relatively high densities of exposed TF. The model predicts that the effect of a severe fXI deficiency depends on the platelet count, and that fXI becomes more important at high platelet counts.

Factor XI: hemostasis, thrombosis, and antithrombosis

Coagulation factor FXI (FXI), a plasma serine protease zymogen, has important roles in both intrinsic and extrinsic coagulation pathways and bridges the initiation and amplification phases of plasmatic hemostasis. Recent studies have provided new insight into the molecular structure and functional features of FXI and have demonstrated distinct structural and biological differences between activated factor XII (FXIIa)-mediated FXI activation and tissue factor/thrombin-mediated FXI activation. The former is important in thrombosis; the latter is more essential in hemostasis. Activated partial thromboplastin tine (aPTT) artificially reflects FXIIa-initiated intrinsic coagulation pathway in vitro. Conversely, FXIIa-inhibited diluted thromboplastin time assay may reflect tissue factor/thrombin-mediated FXI activation in vivo. Further explication of the genetic mutations of FXI deficiency has improved the understanding of the structure-function relationship of FXI. Besides its procoagulant activity, the antifibrinolytic activity of FXI was well documented in a wealth of literature. Finally, the new emerging concept of inhibiting FXI as a novel antithrombotic approach with an improved benefit-risk ratio has been supported through observations from human FXI deficiency and various animal models. Large- and small-molecule FXI inhibitors have shown promising antithrombotic effects. The present review summarizes the recent advancements in the molecular physiology of FXI and the molecular pathogenesis of FXI deficiency and discusses the evidence and progress of FXI-targeting antithrombotics development.

Revisiting the molecular epidemiology of factor XI deficiency: nine new mutations and an original large 4qTer deletion in western Brittany (France)

Constitutional deficiency in factor XI (FXI) is a rare bleeding disorder in the general population, with the exception of Ashkenazi Jews. During the last decade, the detection of FXI-deficient patients has shifted from clinical screening identifying mostly severe bleeders to biological screening combining findings of prolonged activated partial thromboplastin time and FXI coagulation activity (FXI:C) below 50 U/dl. The goal of this study was to determine the molecular basis of FXI deficiency in western Brittany, France. Over the course of four years, we detected 98 FXI-deficient patients through biological screening, and 44 patients agreed to participate in this study corresponding to 25 index cases. We developed an efficient mutation detection strategy (combining direct sequencing and QFM-PCR to search for heterozygous rearrangements in a routine setting) that detected F11 mutations in 24 out of the 25 index cases. An unexpected allelic heterogeneity was found, with 14 different single point mutations being detected, among which nine are new. Moreover, a large heterozygous deletion of the entire F11 gene was detected, and was then further defined using a CGH array as a 4q34.2 telomeric deletion of 7 Mb containing 77 genes. We propose that the observed recurrent mutations may be considered as genetic tags of a population. This study highlights the importance of screening for large deletions in molecular studies of F11 .

Inherited bleeding disorders in pregnancy

Women with inherited bleeding disorders may face several haemostatic challenges during pregnancy and childbirth. Pregnancy in these women requires specialised and individualised care. Prenatal diagnosis is primarily considered in families affected by severe bleeding disorder such as haemophilia. Non-invasive fetal sex determination by analysis of free fetal DNA in maternal blood offers carriers of haemophilia a means of avoiding invasive testing and its associated risks in female pregnancies. With the exception of fibrinogen and factor XIII deficiencies, it is currently unclear whether women with inherited bleeding disorders are at increased risk of miscarriage or antepartum haemorrhage. However, they are at increased risk of primary and secondary postpartum haemorrhage. The fetus, if severely affected, is at risk of cranial bleeding during labour and delivery. Appropriate haemostatic cover during labour and delivery, avoidance of prolonged labour and traumatic delivery, and active management of third stage of labour can minimise the risk of bleeding complications for the mother and her fetus.

Polyphosphate is a cofactor for the activation of factor XI by thrombin

Factor XI deficiency is associated with a bleeding diathesis, but factor XII deficiency is not, indicating that, in normal hemostasis, factor XI must be activated in vivo by a protease other than factor XIIa. Several groups have identified thrombin as the most likely activator of factor XI, although this reaction is slow in solution. Although certain nonphysiologic anionic polymers and surfaces have been shown to enhance factor XI activation by thrombin, the physiologic cofactor for this reaction is uncertain. Activated platelets secrete the highly anionic polymer polyphosphate, and our previous studies have shown that polyphosphate has potent procoagulant activity. We now report that polyphosphate potently accelerates factor XI activation by α-thrombin, β-thrombin, and factor XIa and that these reactions are supported by polyphosphate polymers of the size secreted by activated human platelets. We therefore propose that polyphosphate is a natural cofactor for factor XI activation in plasma that may help explain the role of factor XI in hemostasis and thrombosis.

A novel missense mutation Asp506Gly in Exon 13 of the F11 gene in an asymptomatic Korean woman with mild factor XI deficiency

Factor XI (FXI) deficiency is a rare autosomal recessive coagulation disorder most commonly found in Ashkenazi and Iraqi Jews, but it is also found in other ethnic groups. It is a trauma or surgery-related bleeding disorder, but spontaneous bleeding is rarely seen. The clinical manifestation of bleeding in FXI deficiency cases is variable and seems to poorly correlate with plasma FXI levels. The molecular pathology of FXI deficiency is mutation in the F11 gene on the chromosome band 4q35. We report a novel mutation of the F11 gene in an 18-year-old asymptomatic Korean woman with mild FXI deficiency. Pre-operative laboratory screen tests for lipoma on her back revealed slightly prolonged activated partial thromboplastin time (45.2 sec; reference range, 23.2-39.4 sec). Her FXI activity (35%) was slightly lower than the normal FXI activity (reference range, 50-150%). Direct sequence analysis of the F11 gene revealed a heterozygous A to G substitution in nucleotide 1517 (c.1517A>G) of exon 13, resulting in the substitution of aspartic acid with glycine in codon 506 (p.Asp506Gly). To the best of our knowledge, the Asp506Gly is a novel missense mutation, and this is the first genetically confirmed case of mild FXI deficiency in Korea.

A retrospective analysis of 157 surgical procedures performed without replacement therapy in 83 unrelated factor VII-deficient patients

BACKGROUND

 Inherited factor (F)VII deficiency is the commonest of the rare bleeding disorders, with a wide set of hemorrhagic features. Other than for the severe clinical forms (for which treatment guidelines are well defined), consistent recommendations regarding perioperative replacement management do not exist for mild and asymptomatic FVII-deficient patients.

OBJECTIVES

 The present study aimed to evaluate the influence of bleeding history, FVII procoagulant activity levels (FVII:C) and the type of surgical procedure on the management of inherited FVII-deficient patients before surgery.

PATIENTS

 One hundred and fifty-seven surgical procedures, performed without replacement therapy, in 83 unrelated FVII-deficient patients (median FVII:C=5%, range 0.6%-35%) were analyzed.

RESULTS

 The overall bleeding rate was 15.3%. We found a significant relationship between previous deep traumatic hematomas and bleeding at surgery, although relationships with previous common epistaxis, easy bruising and menorrhagia were not significant. The receiver-operating characteristic (ROC) curve analysis performed on the first 83 procedures allowed us to define a cut-off value of 7% with a sensitivity of 87% (negative predictive value: 94%). To enhance the sensitivity, and to take into account the potential variation resulting from non-standardized FVII:C measurements, we would suggest applying a threshold of 10%.

CONCLUSION

 We have proposed recommendations for the perioperative management of FVII-deficient patients based on FVII:C levels, a thorough bleeding history and the type of surgery involved. By applying these recommendations, minor procedures that risk only external or controlled hemorrhage can be performed in asymptomatic or mildly affected adults, even those with FVII:C levels below 10%.

Three dominant-negative mutations in factor XI-deficient patients

Factor XI (FXI) deficiency results from genetic defects of the F11 gene and is generally considered to be inherited in an autosomal recessive manner. However, the homodimeric structure of FXI allows, in some cases, the dominant-negative transmission of the disease. The aim of this study was to characterize novel missense mutations in three unrelated patients and verify the dominant-negative effects of these mutations on the secretion of wild-type FXI protein by expression studies. The F11 gene was PCR amplified, from genomic DNA extracted from peripheral blood, and sequenced on an ABI 3100 Genetic Analyzer. Human wild-type FXI and FXI mutants were expressed in BHK570 cells using Lipofectamin transfection reagents. Conditioned media and cell lysates were collected for the measurement of luciferase activity, FXI antigen and Western blot analysis. DNA sequencing revealed three novel missense F11 mutations; c.127G>A in exon 3 (Ala43Thr), c.723C>G in exon 7 (Phe241Leu) and c.1207G>A in exon 11 (Val403Met). In vitro expression studies showed that the mutation Ala43Thr, Phe241Leu or Val403Met remarkably decreased the extracellular secretion of mutant FXI, rather than reducing synthesis of the mutant proteins. Cotransfection of wild-type FXI with mutant FXI constructs indicated that the mutation Ala43Thr, Phe241Leu or Val403Met reduced the secretion of wild-type FXI by 75.9%, 68.6% or 71.4%, respectively. Our study suggests that dominant-negative mutations in FXI-deficient patients of non-Ashkenazi Jewish origin may be more prevalent than thought, resulting from FXI's unique dimeric structure.

Elevated factor VIII enhances thrombin generation in the presence of factor VIII-deficiency, factor XI-deficiency or fondaparinux

BACKGROUND

Increased levels of factor VIII occur as a response to vascular injury and/or inflammation, and may increase thrombotic risks. In contrast, factor VIII deficiency poses a major hemostatic challenge. The role of factor VIII in modulating hemostasis/thrombosis was investigated in plasma models of hypocoagulable and hypercoagulable state using thrombin generation (TG) assay.

METHODS

TG was performed in undiluted/diluted control, FVIII-deficient, FVIII-deficient with low antithrombin (AT activity, ~59%), and factor XI-deficient plasma samples using relipidated tissue factor (TF, 2 pM) or dilute Actin as activators. The impact of elevated FVIII on TG was simulated by adding Humate-P (0 to 3 U/ml) to the above plasma samples. In fondaparinux (1 μg/ml) treated plasma with normal or lower AT activity effects of Humate-P vs. 60 nM of recombinant activated factor VII (rFVIIa) were also evaluated.

RESULTS

Humate-P increased TG concentration dependently in undiluted and diluted control plasma with TF activation. With Actin activation, only the concentration dependent shortening of lag time, but no change in peak thrombin was observed. In FVIII-deficient, FVIII-deficient with low AT, and FXI-deficient samples, 3 U/ml of Humate-P increased TG, and decreased its onset with either activator. The reduced peak thrombin due to fondaparinux was reversed with Humate-P (3 U/ml) more than with rFVIIa. Elevated FVIII levels seem to favor intrinsic tenase formation and antagonize fondaparinux because anti-FIXa aptamer added to fondaparinux effectively attenuated TG.

CONCLUSION

Elevated FVIII supports the propagation of TG via intrinsic tenase formation under low TF condition, factor XI deficiency or in the presence of fondaparinux.

Coagulation factor XI as a novel target for antithrombotic treatment

Coagulation factor (F)XI was first described as a member of the contact pathway of coagulation. However, the 'classic' theory of the extrinsic and intrinsic pathway has been revised and FXI was found to be activated by thrombin and to play a role in sustained thrombin generation and fibrinolysis inhibition. Recent studies have pointed to a disproportionate role of FXI in thrombosis and hemostasis. The observations that human congenital FXI deficiency is generally accompanied by mild and injury-related bleeding, and that experimental, provoked bleeding in animals is unaffected by FXI deficiency or FXI inhibition, suggest that the FXI amplification pathway is less important for normal hemostasis in vivo. In contrast, elevated plasma levels of FXI may contribute to human thromboembolic disease and the antithrombotic efficacy of FXI inhibition has been demonstrated in numerous animal models of arterial, venous and cerebral thrombosis. Whether severe FXI deficiency in humans protects against thromboembolic events remains unclear, although some evidence exists that the occurrence of ischemic stroke or venous thrombosis is low in severely FXI-deficient patients. Because of its distinctive function in thrombosis and hemostasis, FXI is an attractive target for the treatment and prevention of thromboembolism. A novel strategy for FXI inhibition is the use of antisense technology which has been studied in various thrombosis and bleeding animal models. The results are promising and support the concept that targeting FXI might serve as a new, effective and potentially safer alternative for the treatment of thromboembolic disease in humans.

Inhibition of the intrinsic coagulation pathway factor XI by antisense oligonucleotides: a novel antithrombotic strategy with lowered bleeding risk

Existing anticoagulants effectively inhibit the activity of coagulation factors of the extrinsic and common pathway but have substantial limitations and can cause severe bleeding complications. Here we describe a novel therapeutic approach to thrombosis treatment. We have developed and characterized the efficacy and safety of selective second-generation antisense oligonucleotides (ASOs) targeting coagulation factor XI (FXI), a member of the intrinsic coagulation pathway. Systemic treatment of mice with FXI ASO led to a potent, specific, and dose-dependent reduction of FXI mRNA levels in the liver with corresponding reductions in plasma levels of FXI protein and activity. FXIASO treatment produced potent, dose-dependent antithrombotic activity in various venous and arterial thrombosis models, comparable with warfarin or enoxaparin. However, unlike warfarin or enoxaparin, FXI inhibition did not cause bleeding. Coadministration of FXI ASO with enoxaparin or the antiplatelet drug clopidogrel produced improved antithrombotic activity without increased bleeding. Finally, plasma-derived FXI concentrate was shown to effectively and rapidly reverse the anticoagulant effect of FXI antisense therapy. These results support the concept that inhibition of FXI through antisense therapy might serve as a new and effective strategy for the treatment and prevention of venous thromboembolism with improved specificity and safety.

Predictors for neonatal thrombocytopenia in infants of thrombocytopenic mothers during pregnancy

BACKGROUND

Although maternal thrombocytopenia during pregnancy is common, its effect on neonatal platelets has not yet been fully evaluated.

METHODS

We retrospectively evaluated the rate of thrombocytopenia among 767 healthy term neonates (gestational age 37-42 weeks) born to 723 mothers with pregnancy-induced thrombocytopenia to define risk factors predicting thrombocytopenia in this group.

RESULTS

Thrombocytopenia was diagnosed in 2.2% of the infants. Multivariate analysis showed that infants with thrombocytopenia were more likely to be male, to be born at lower gestational age and to have lower birth weight associated with lower maternal platelets counts. Maternal platelet counts of 100-149 x 10(9)/L, 50-99 x 10(9)/L, and <50 x 10(9)/L corresponded respectively to 1.7%, 4.3%, and 12.5% of neonatal thrombocytopenia (P = 0.031).

CONCLUSIONS

Routine blood counts are recommended, in particular for male infants with low birth weight born to mothers with moderate-to-severe thrombocytopenia.

Coagulation procofactor activation by factor XIa

SUMMARY BACKGROUND

In the extrinsic pathway, the essential procofactors factor (F) V and FVIII are activated to FVa and FVIIIa by thrombin. In the contact pathway and its clinical diagnostic test, the activated partial thromboplastin time (APTT) assay, the sources of procofactor activation are unknown. In the APTT assay, FXII is activated on a negatively charged surface and proceeds to activate FXI, which activates FIX upon the addition of Ca(2+). FIXa feeds thrombin generation through activation of FX. FIXa is an extremely poor catalyst in the absence of its FVIIIa cofactor, which, in the intrinsic FXase complex, increases FXa generation by approximately 10(7). One potential APTT procofactor activator in this setting is FXIa.

OBJECTIVE

To test the hypothesis that FXIa can activate FVIII and FV.

METHODS

Recombinant FVIII and plasma FV were treated with FXIa, and the activities and integrities of each procofactor were measured using commercial clotting assays and sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

Kinetic analyses of FXIa-catalyzed activation and inactivation of FV and FVIII are reported, and the the timing and sites of cleavage are defined.

CONCLUSIONS

FXIa activates both procofactors at plasma protein concentrations, and computational modeling suggests that procofactor activation during the preincubation phase of the APTT assay is critical to the performance of the assay. As the APTT assay is the primary tool for the diagnosis and management of hemophilias A and B, as well as in the determination of FVIII inhibitors, these findings have potential implications in the clinical setting.

Inhibition of Factor XIa as a New Approach to Anticoagulation

The dose-limiting issue with available anticoagulant therapies is bleeding. Is there an approach that could provide antithrombotic protection with reduced bleeding? One hypothesis is that targeting proteases upstream from the common pathway provides a reduction in thrombin sufficient to impede occlusive thrombosis yet allows enough thrombin generation to support hemostasis. The impairment of intrinsic coagulation by selective inhibition of factor XI (FXI) leaves the extrinsic and common pathways of coagulation intact, making FXI a drug target. This concept is supported by the observation that human deficiency in FXI results in a mild bleeding disorder compared with other coagulation factor deficiencies, and that elevated levels of FXI are a risk factor for thromboembolic disease. Moreover, FXI knockout mice have reduced thrombosis with little effect on hemostasis. The results from genetic models have been supported by studies using neutralizing antibodies, peptide inhibitors, and small-molecule inhibitors. These agents impede thrombosis without affecting bleeding time in a variety of experimental animals, including primates. Together, these data strongly support FXIa inhibition as a viable method to increase the ratio of benefit to risk in an antithrombotic drug.

Structure and function of factor XI

Factor XI (FXI) is the zymogen of an enzyme (FXIa) that contributes to hemostasis by activating factor IX. Although bleeding associated with FXI deficiency is relatively mild, there has been resurgence of interest in FXI because of studies indicating it makes contributions to thrombosis and other processes associated with dysregulated coagulation. FXI is an unusual dimeric protease, with structural features that distinguish it from vitamin K-dependent coagulation proteases. The recent availability of crystal structures for zymogen FXI and the FXIa catalytic domain have enhanced our understanding of structure-function relationships for this molecule. FXI contains 4 "apple domains" that form a disk structure with extensive interfaces at the base of the catalytic domain. The characterization of the apple disk structure, and its relationship to the catalytic domain, have provided new insight into the mechanism of FXI activation, the interaction of FXIa with the substrate factor IX, and the binding of FXI to platelets. Analyses of missense mutations associated with FXI deficiency have provided additional clues to localization of ligand-binding sites on the protein surface. Together, these data will facilitate efforts to understand the physiology and pathology of this unusual protease, and development of therapeutics to treat thrombotic disorders.

Cataract extraction without prophylactic treatment in patients with severe factor XI deficiency

PURPOSE

To assess the risks of intraoperative and postoperative bleeding associated with cataract extraction without prophylactic treatment in patients with severe factor XI (FXI) deficiency.

DESIGN

Prospective interventional case series.

METHODS

SETTING

Single institute.

STUDY POPULATION

Consecutive unrelated patients with severe FXI deficiency who underwent cataract extraction under topical anesthesia, with a clear corneal incision, phacoemulsification, and implantation of a foldable posterior chamber intraocular lens (PCIOL) were enrolled. Patients with associated intraocular conditions that could complicate the surgery were excluded.

INTERVENTION

Cataract extraction without prophylactic treatment for the FXI deficiency.

MAIN OUTCOME MEASURES

Assessment of intraoperative and postoperative ocular bleeding and other related complications.

RESULTS

Seven patients ranging in age from 61 to 95 years (median, 79) underwent phacoemulsification and PCIOL implantation in 11 eyes. Five patients (71%) were homozygotes for type II mutation of the FXI gene (activity level of <1 U/dl), 1 patient was a homozygote for type III mutation (activity level of 11 U/dl), and 1 patient was a compound heterozygote for types II and III (activity level of 3 U/dl). Three of the patients (43%), all type II homozygotes, also had an inhibitor antibody to FXI. All 7 patients were followed for at least 1 week after the operation. The surgery was uneventful in all eyes, and neither major nor minor bleeding events were observed in any of the operated eyes during surgery and follow-up.

CONCLUSIONS

Cataract extraction by phacoemulsification in uncomplicated eyes can be performed safely without prophylactic treatment in patients with severe FXI deficiency with or without inhibitor antibodies against FXI.

First diagnosis of factor XI deficiency in a patient with subarachnoid haemorrhage

Aneurismal subarachnoid haemorrhage (SAH) is a devastating event affecting patients at a fairly young age and accounting for significant morbidity and mortality. Although there is progress concerning diagnostic methods and treatment, this case report might add interesting data to the current understanding of this disease and its clinical management with respect to circumstantial deficiency of the coagulation factor XI (FXI). In this report, we present a unique case of aneurismal SAH in a patient with underlying coagulation FXI deficiency which was incidentally identified after patient's admission, as routine blood tests revealed increased activated partial thromboplastin time. Despite early successful treatment with coiling, the patient had a second episode of SAH a few months after his discharge, due to aneurysm revascularization and rupture. Molecular analysis and identification of new mutations were performed. We describe management of SAH with respect to a coexisting bleeding disorder; also testing of patient's family members for FXI deficiency and decisions about screening for intracranial aneurysm are described. Late complications of SAH are - among others - aneurysm revascularization and rebleeding. Although FXI deficiency could be considered an exacerbating factor, it cannot be definitely implicated.

Identification of coagulation factor XI as a ligand for platelet apolipoprotein E receptor 2 (ApoER2)

OBJECTIVE

Factor XI (FXI) promotes hemostasis and thrombosis through enhancement of thrombin generation and has been shown to play a critical role in the formation of occlusive thrombi in arterial injury models. The aim of this study was to investigate the mechanisms governing interactions between FXI and platelets.

METHODS AND RESULTS

Platelet adhesion to immobilized FXI was abrogated in the presence of the low-density lipoprotein (LDL) receptor antagonist, receptor-associated protein (RAP), soluble recombinant apolipoprotein E receptor 2 (ApoER2), or the LDL-binding domain 1 or 2 of ApoER2. FXI supported wild-type murine platelet binding; in contrast, ApoER2-deficient murine platelets did not adhere to FXI. In the presence of shear, platelet aggregates formed on FXI or activated FXI (FXIa) surfaces, whereas the presence of RAP, binding domain 1 of ApoER2, or an anti-GPIb alpha mAb blocked platelet adhesion to FXI or FXIa under shear. Soluble FXI bound to immobilized ApoER2' with an affinity of 61 nmol/L.

CONCLUSIONS

This study has identified apolipoprotein E receptor 2 (ApoER2, LRP8), a member of the LDL receptor family, as a platelet receptor for FXI. The interaction of FXI with other cell types that express ApoER2 remains to be explored.

[Appropriate laboratory investigation in women with menorrhagia]

Inherited bleeding disorders are potentially causes of menorrhagia and must be investigated if no specific cause is identified. The reported prevalence of inherited bleeding disorders is high in women with menorrhagia compared to the general population. The most frequent disorders reported are von Willebrand's disease and Factor XI deficiency. Menorrhagia is, also, a frequent finding in women with congenital bleeding disorders. Morever, menorrhagia represents the major cause of iron-deficiency anemia among women of reproductive age. Primary evaluation for an underlying disorder of hemostasis in a woman wih menorrhagia is a focused history for familiy and personal history of bleeding symptoms and a complete blood cell count. This will rule out thrombocytopenic bleeding and also assesses for the degree, if any, of anemia. Those women with a positive screen and normal platelet count should be evaluated with laboratory investigation including prothrombin time, activated partial thromboplastin time, factor VIII, VWF ristocetin cofactor and antigen. If initial hemostasis testing above is normal, then further hemostasis testing can be considered, especially in terms of platelet aggregation, in a multidisciplinary clinic.

Study of Association Between Hypertensive Disorders of Pregnancy and the Human Coagulation Factor XI Gene

OBJECTIVE

Hypertensive disorders of pregnancy (HDP) are among the most common and serious complications of pregnancy. Persuasive evidence implicaties genetic factors in the genesis of HDP. The aim of the present study was to assess the association between single-nucleotide polymorphisms (SNPs) in the human coagulation factor XI (F11) gene and HDP, by conducting a haplotype-based case-control study.

METHODS

We chose 3 SNPs (rs925453, rs925451, and rs12500151) in the human F11 gene as genetic markers. We then conducted an association study with 77 HDP patients and 154 age-matched non-HDP subjects.

RESULTS

The frequency of rs925453 genotypes significantly differed between the two groups. The frequency of the T-G-G haplotype was significantly higher in the HDP group than in the non-HDP group (p = 0.0002).

CONCLUSIONS

The T allele of rs925453 and the T-G-G haplotype appear to be useful genetic markers of HDP.

Factor XI deficiency in humans

Factor XI (FXI) deficiency is an autosomal recessive injury-related bleeding tendency, which is common in Jews particularly of Ashkenazi origin. To date, 152 mutations in the FXI gene have been reported with four exhibiting founder effects in specific populations, Glu117stop in Ashkenazi and Iraqi Jews and Arabs, Phe283Leu in Ashkenazi Jews, Cys38Arg in Basques, and Cys128stop in the United Kingdom. Severe FXI deficiency does not confer protection against acute myocardial infarction, but is associated with a reduced incidence of ischemic stroke. Inhibitors to FXI develop in one-third of patients with very severe FXI deficiency following exposure to blood products. Therapy for prevention of bleeding during surgery in patients with severe FXI deficiency consists of plasma, factor XI concentrates, fibrin glue and antifibrinolytic agents. In patients with an inhibitor to FXI, recombinant factor VIIa is useful.

Prevention of vascular graft occlusion and thrombus-associated thrombin generation by inhibition of factor XI

The protease thrombin is required for normal hemostasis and pathologic thrombogenesis. Since the mechanism of coagulation factor XI (FXI)-dependent thrombus growth remains unclear, we investigated the contribution of FXI to thrombus formation in a primate thrombosis model. Pretreatment of baboons with a novel anti-human FXI monoclonal antibody (aXIMab; 2 mg/kg) inhibited plasma FXI by at least 99% for 10 days, and suppressed thrombin-antithrombin (TAT) complex and beta-thromboglobulin (betaTG) formation measured immediately downstream from thrombi forming within collagen-coated vascular grafts. FXI inhibition with aXIMab limited platelet and fibrin deposition in 4-mm diameter grafts without an apparent increase in D-dimer release from thrombi, and prevented the occlusion of 2-mm diameter grafts without affecting template bleeding times. In comparison, pretreatment with aspirin (32 mg/kg) prolonged bleeding times but failed to prevent graft occlusion, supporting the concept that FXI blockade may offer therapeutic advantages over other antithrombotic agents in terms of bleeding complications. In whole blood, aXIMab prevented fibrin formation in a collagen-coated flow chamber, independent of factor XII and factor VII. These data suggest that endogenous FXI contributes to arterial thrombus propagation through a striking amplification of thrombin generation at the thrombus luminal surface.

Novel roles for factor XII-driven plasma contact activation system

PURPOSE OF REVIEW

Blood coagulation is a tightly regulated process, involving vascular endothelium, platelets, and plasma coagulation factors. Formation of fibrin involves a series of sequential proteolytic reactions, initiated by the 'extrinsic' and 'intrinsic' pathway of coagulation. As hereditary deficiency of factor XII, the protease that triggers the intrinsic pathway and the kallikrein-kinin system, is not associated with a bleeding disorder or other disease states, the physiological role of factor XII is unknown.

RECENT FINDINGS

Patient studies, genetically altered mouse models, and plasma assays analyzed functions of the factor XII-driven contact activation system for coagulation and inflammation. This review focuses on articles, which report phenotypization of animals deficient in the contact system proteins factor XII, factor XI and high-molecular-weight kininogen, as well as novel links between factor XII and edema formation, discovery of new in-vivo activators of factor XII, and functions of the factor XII downstream protease factor XI.

SUMMARY

Recent studies improved understanding of the factor XII-driven contact system in hemostasis, thrombosis, and inflammation. Studies in mouse models revealed that deficiency in contact system proteins protects from arterial thrombus formation, but does not affect hemostasis. Targeting contact system proteins offers new opportunities for safe anticoagulation associated with minimal bleeding risk. Furthermore, targeting factor XII activity provides an opportunity to treat edema formation.

Use of a preoperative bleeding questionnaire in pediatric patients who undergo adenotonsillectomy

Objective

To determine the efficacy of a preoperative bleeding questionnaire (POBQ) and coagulation screening in predicting hemorrhage associated with adenotonsillectomy.

Study Design

Retrospective study.

Subjects and Methods

Between January 1998 and December 2003, 7730 tonsillectomy and adenotonsillectomy patients were administered the POBQ preoperatively. Further coagulation screening was based on POBQ responses.

Results

A total of 232 (3.0%) of 7730 had postoperative bleeding; 184 (3.2%) of 5782 patients who had negative questionnaires bled postoperatively compared with 48 (2.5%) of 1948 patients with positive questionnaires ( P = 0.126). Of 1948 patients with positive questionnaires, 141 (7.2%) had abnormal preoperative coagulation screens and 9 (6.4%) of 141 bled; of the 1807 (92.8%) with negative coagulation screens, 39 (2.2%) bled ( P = 0.005).

Conclusion

The POBQ is an effective tool for identifying patients who are at potential risk for post-tonsillectomy bleeding. Patients with both a positive POBQ and coagulation screen had a statistically higher likelihood of postoperative bleeding than other patients. The POBQ allowed the identification of individuals with bleeding disorders to be treated before surgery, likely decreasing the risk of bleeding in these patients.

[Use of recombinant, activated Factor VII in the treatment and prevention of bleeding complications in two female patients suffering from congenital XI factor deficiency during orthopedic and traumatology intervention. Case reports]

The authors describe the treatment of the bleeding complications in two female patients suffering from a rare, inherited coagulation disorder; Factor XI deficiency after having major orthopaedic and traumatologic operations by activated, recombinant Factor VII (NovoSeven, Novo Nordisk, Bagsvaerd, Denmark). In the first case a total hip arthroplasty was performed because of severe, left-sided osteoarthritis. Despite of the standard protocol prescribed by the National Haemophilia Centre, severe bleeding complication occurred. The authors describe the pattern of the postoperative bleeding, the difficult decision on reoperation and the experience with activated, recombinant Factor VII, as a rescue treatment. In the second case the patient had a right femoral head fracture after falling. In her anamnesis it was known that she had severe bleeding complications despite factor substitution. After discussion with the National Haemophilia Centre operation was made by the use of NovoSeven.

Survival advantage of coagulation factor XI-deficient mice during peritoneal sepsis

Anticoagulation is a rational approach to the treatment of sepsis-associated consumptive coagulopathy, but its application is limited because of the risk of excessive bleeding. Factor XI (FXI) contributes substantially to pathological blood coagulation (thrombosis), whereas it contributes only modestly to normal hemostasis. We found that FXI-deficient mice have reduced coagulopathy and increased survival relative to FXI-expressing wild-type mice during cecal ligation and puncture-induced acute peritonitis/sepsis. This finding suggests that FXI contributes to coagulopathy and/or inflammation during sepsis and that pharmacologic inhibition of FXI activity may alter the course and outcome of some infections.

Factor XI deficiency

Although factor XI (FXI) deficiency has a particularly high incidence in Ashkenazi Jews, it is now frequently diagnosed in other ethnic groups. This review gives an overview of the basic pathophysiology, clinical manifestations, and management of FXI deficiency. The correlation between FXI levels and the bleeding phenotype is much less clear than in the haemophilias, and consequently the bleeding risk can be difficult to predict. Two well-characterized mutations in the F11 gene are responsible for the majority of Jewish cases, but new mutations are becoming increasingly recognized. The publication of the crystal structure has greatly enhanced our understanding of the structure-function relationship in FXI. The impact of recent studies on our understanding of the role of FXI in coagulation is discussed.

Reduced incidence of ischemic stroke in patients with severe factor XI deficiency

Inherited disorders of hemostasis are natural models for investigating mechanisms of thrombosis and development of antithrombotic therapy. Because mice with total factor XI deficiency are protected against ischemic stroke and do not manifest excessive bleeding, we investigated the incidence of ischemic stroke in patients with severe inherited factor XI deficiency. Incidence of ischemic stroke in 115 patients aged 45 years or more with severe factor XI deficiency (activity less than 15 U/dL) was compared with incidence in the Israeli population as estimated from a stroke survey of 1528 patients. Adjustment for major risk factors of stroke (hypertension, diabetes mellitus, hypercholesterolemia, current smoking) was based on comparison of their prevalence in the stroke survey to an Israeli health survey of 9509 subjects. Incidence of myocardial infarction in the factor XI cohort was also recorded. After adjustment for the 4 major risk factors of ischemic stroke, the expected incidence of ischemic stroke was 8.56 compared with one observed (P = .003). The reduced 1:115 incidence of ischemic stroke contrasted with a 19:115 incidence of myocardial infarction, similar to the expected incidence. Thus, severe factor XI deficiency probably is protective against ischemic stroke but not against acute myocardial infarction.

Induction of an inhibitor antibody to factor XI in a patient with severe inherited factor XI deficiency by Rh immune globulin

In this paper, we report an inhibitor antibody to factor XI (FXI) in a woman with severe inherited FXI deficiency, induced by FXI present in an Rh immune globulin preparation. The patient is homozygous for the Glu117Stop mutation, associated with a FXI level of less than 1 U/dL. Unlike all previously described patients with severe FXI deficiency and an inhibitor, the patient had never been exposed to blood products. Following 3 injections of Rh immune globulin during pregnancy, she developed an inhibitor to FXI (8 Bethesda units) that was shown to bind specifically to FXI and inhibit factor IX cleavage by purified FXIa. The administered Rh immune globulin and 2 other similar products were shown to contain FXI. Clinicians should be aware of the potential for immunization of severely FXI-deficient patients by FXI present in Rh immune globulin preparations.

Characterization of Novel Forms of Coagulation Factor XIa: independence of factor XIa subunits in factor IX activation

Factor XI is the zymogen of a dimeric plasma protease, factor XIa, with two active sites. In solution, and during contact activation in plasma, conversion of factor XI to factor XIa proceeds through an intermediate with one active site (1/2-FXIa). Factor XIa and 1/2-FXIa activate the substrate factor IX, with similar kinetic parameters in purified and plasma systems. During hemostasis, factor IX is activated by factors XIa or VIIa, by cleavage of the peptide bonds after Arg145 and Arg180. Factor VIIa cleaves these bonds sequentially, with accumulation of factor IX alpha, an intermediate cleaved after Arg145. Factor XIa also cleaves factor IX preferentially after Arg145, but little intermediate is detected. It has been postulated that the two factor XIa active sites cleave both factor IX peptide bonds prior to releasing factor IX abeta. To test this, we examined cleavage of factor IX by four single active site factor XIa proteases. Little intermediate formation was detected with 1/2-FXIa, factor XIa with one inhibited active site, or a recombinant factor XIa monomer. However, factor IX alpha accumulated during activation by the factor XIa catalytic domain, demonstrating the importance of the factor XIa heavy chain. Fluorescence titration of active site-labeled factor XIa revealed a binding stoichiometry of 1.9 +/- 0.4 mol of factor IX/mol of factor XIa (Kd = 70 +/- 40 nm). The results indicate that two forms of activated factor XI are generated during coagulation, and that each half of a factor XIa dimer behaves as an independent enzyme with respect to factor IX.

Optimal management of an aneurysmal subarachnoid hemorrhage in a patient with known factor XI deficiency: a case report

The authors report a rare case of an acute cerebral aneurysm rupture in a patient with a known factor XI deficiency. Aneurysmal subarachnoid hemorrhage (SAH) accounts for a high mortality and morbidity rate. When SAH is associated with an inherited coagulation disorder such as hemophilia C, an unexpected and possible increase in hemorrhagic stroke and increase in bleeding during surgery and in the postoperative period could lead to an extremely bad outcome. Clinical management consists of rapid correction of the coagulation disorder before undergoing any invasive intracranial procedure. Such an optimal therapeutic strategy must be under the care of a multidisciplinary medical and surgical team. Human factor XI concentrate (Hemoleven, Laboratoire Français du Fractionnement et des Biotechnologies [LFB], Les Ulis, France) was used successfully in this case report. New treatment using recombinant factor VIIa is discussed.

Uneventful cesarean delivery with administration of factor XI concentrate in a patient with severe factor XI deficiency

Factor XI (FXI) is a procoagulant factor and antifibrinolytic agent, and its absence causes a bleeding tendency. FXI deficiency is autosomal in inheritance, with severe FXI deficiency in homozygotes and partial deficiency in heterozygotes. A 24-year-old primigravida with an uneventful pregnancy and no history of bleeding manifestations was admitted to our department at 38 weeks of gestation. Her blood count and serum biochemistry findings were normal except for a coagulation screen, which revealed a prolonged activated partial thromboplastin time (APTT) of 63 seconds (normal range, 24-35 seconds). The measured FXI coagulant activity of 8 IU/dL (reference range, 70-150 IU/dL) established a diagnosis of severe FXI deficiency. The breech presentation of the fetus prompted the decision for cesarean delivery under general anesthesia. We administered a single dose of FXI concentrate (15 IU/kg), which corrected the APTT to 34 seconds. The cesarean delivery was uncomplicated, and postpartum recovery of the mother and her baby was uneventful with no bleeding complications. The finding of an isolated prolonged APTT should prompt obstetricians to consider FXI deficiency. The appropriate use of factor FXI concentrate in managing obstetric patients with FXI deficiency can minimize potential bleeding complications and ensure an optimal outcome for both mother and neonate.

Intrinsic pathway of coagulation and arterial thrombosis

Formation of a fibrin clot is mediated by a group of tightly regulated plasma proteases and cofactors. While this system is essential for minimizing blood loss from an injured blood vessel (hemostasis), it also contributes to pathologic fibrin formation and platelet activation that may occlude vessels (thrombosis). Many antithrombotic drugs target key elements of the plasma coagulation mechanism such as thrombin and factor Xa, based on the premise that plasma elements contributing to thrombosis are primarily those involved in hemostasis. Recent studies with genetically altered mice raise questions about this paradigm. Deficiencies of the intrinsic pathway proteases factor XII and factor XI are not associated with abnormal hemostasis in mice, but impair formation of occlusive thrombi in arterial injury models, indicating that pathways not essential for hemostasis participate in arterial thrombosis. If factor XII or factor XI make similar contributions to thrombosis in humans, these proteases could be ideal targets for drugs to treat or prevent thromboembolic disease with minimal risk of therapy-associated bleeding.

A novel mutation (Gln433Glu) in exon 12 combined with the G insertion in exon 13 causes severe factor XI deficiency in Japanese patients

Factor XI (FXI) deficiency is an autosomal, incompletely recessive coagulopathy. This disorder is rare in the general population worldwide, but is one of the most common inherited diseases in Ashkenazi Jews. It has been reported that a significantly higher frequency of allelic heterogeneity occurs in different ethnic groups. The study objective was to study the molecular basis of this disease in a Japanese family. Two Japanese brothers with severe FXI deficiency and three other family members were screened by direct sequencing analysis after polymerase chain reaction. We identified a novel mutation, a C-to-G transition at position 1394 in exon 12 in the FXI gene (F11 c.1394 C>G). This transition resulted in a missense mutation (Gln433Glu), which led to the disruption of the catalytic domain structure of the FXI molecule. This change, combined with a G insertion in exon 13 (501/502 ins G), led to a frameshift mutation, which has previously been reported in only one other Japanese patient. In conclusion, the compound heterozygous novel mutations that cause severe FXI deficiency were found in Japanese patients.