Biology of factor XI.

ABSTRACT: Unique among coagulation factors, the coagulation factor XI (FXI) arose through a duplication of the gene KLKB1, which encodes plasma prekallikrein. This evolutionary origin sets FXI apart structurally because it is a homodimer with 2 identical subunits composed of 4 apple and 1 catalytic domain. Each domain exhibits unique affinities for binding partners within the coagulation cascade, regulating the conversion of FXI to a serine protease as well as the selectivity of substrates cleaved by the active form of FXI. Beyond serving as the molecular nexus for the extrinsic and contact pathways to propagate thrombin generation by way of activating FIX, the function of FXI extends to contribute to barrier function, platelet activation, inflammation, and the immune response. Herein, we critically review the current understanding of the molecular biology of FXI, touching on some functional consequences at the cell, tissue, and organ level. We conclude each section by highlighting the DNA mutations within each domain that present as FXI deficiency. Together, a narrative review of the structure-function of the domains of FXI is imperative to understand the etiology of hemophilia C as well as to identify regions of FXI to safely inhibit the pathological function of activation or activity of FXI without compromising the physiologic role of FXI.

Factor XI inhibitors: cardiovascular perspectives.

Anticoagulants are the cornerstone for prevention and treatment of thrombosis but are not completely effective, and concerns about the risk of bleeding continue to limit their uptake. Animal studies and experience from patients with genetic coagulation factor XI deficiency suggesting that this factor is more important for thrombosis than for haemostasis raises the potential for drugs that target factor XI to provide safer anticoagulation. Multiple factor XI inhibitors are currently under evaluation in clinical trials, including parenterally administered antisense oligonucleotides, monoclonal antibodies, and orally active small-molecule inhibitors. Promising results of phase 2 trials in patients undergoing major orthopaedic surgery, and in those with end-stage kidney disease, atrial fibrillation and acute coronary syndromes have led to large phase 3 trials that are currently ongoing. We here review premises for the use of these agents, results so far accrued, ongoing studies, and perspectives for future patient care.

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 (Kd = 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.

Discovery of Teleost Plasma Kallikrein/Coagulation Factor XI-Like Gene from Channel Catfish (Ictalurus punctatus) and the Evidence that the Protein Encoded by it Acts as a Lectin.

Mammalian plasma kallikrein (PK) and coagulation factor XI (fXI) are serine proteases that play in the kinin-kallikrein cascade and in the blood clotting pathway. These proteases share sequence homology and have four apple domains (APDs) and a serine protease domain (SPD) from their N-terminus to C-terminus. No homologs of these proteases are believed to be present in fish species, except for lobe-finned fish. Fish, however, have a unique lectin, named kalliklectin (KL), which is composed of APDs only. In the present study, we found genomic sequences encoding a protein with both APDs and SPD in a few cartilaginous and bony fishes, including the channel catfish Ictalurus punctatus, using bioinformatic analysis. Furthermore, we purified two ~ 70 kDa proteins from the blood plasma of the catfish using mannose-affinity and gel filtration chromatography sequentially. Using de novo sequencing with quadrupole time-of-flight tandem mass spectrometry, several internal amino acid sequences in these proteins were mapped onto possible PK/fXI-like sequences that are thought to be splicing variants. Exploration of APD-containing proteins in the hagfish genome database and phylogenetic analysis suggested that the PK/fXI-like gene originated from hepatocyte growth factor, and that the gene was acquired in a common ancestor of jawed fish. Synteny analysis provided evidence for chromosomal translocation around the PK/fXI-like locus that occurred in the common ancestor of holosteans and teleosts after separation from the lobe-finned fish lineage, or gene duplication into two chromosomes, followed by independent gene losses. This is the first identification of PK/fXI-like proteins in teleosts.

A focus on dominant negative variants in a series of 170 heterozygous FXI-deficient patients.

INTRODUCTION: Dominant-negative effects have been described for 10 F11 variants in the literature. AIM: The current study aimed at identifying putative dominant-negative F11 variants. MATERIAL AND METHODS: This research consisted in a retrospective analysis of routine laboratory data. RESULTS: In a series of 170 patients with moderate/mild factor XI (FXI) deficiencies, we identified heterozygous carriers of previously reported dominant-negative variants (p.Ser243Phe, p.Cys416Tyr, and p.Gly418Val) with FXI activities inconsistent with a dominant-negative effect. Our findings also do not support a dominant-negative effect of p.Gly418Ala. We also identified a set of patients carrying heterozygous variants, among which five out of 11 are novel, with FXI activities suggesting a dominant-negative effect (p.His53Tyr, p.Cys110Gly, p.Cys140Tyr, p.Glu245Lys, p.Trp246Cys, p.Glu315Lys, p.Ile421Thr, p.Trp425Cys, p.Glu565Lys, p.Thr593Met, and p.Trp617Ter). However, for all but two of these variants, individuals with close to half normal FXI coagulant activity (FXI:C) were identified, indicating an inconstant dominant effect. CONCLUSION: Our data show that for some F11 variants recognized has having dominant-negative effects, such effects actually do not occur in many individuals. The present data suggest that for these patients, the intracellular quality control mechanisms eliminate the variant monomeric polypeptide before homodimer assembly, thereby allowing only the wild-type homodimer to assemble and resulting in half normal activities. In contrast, in patients with markedly decreased activities, some mutant polypeptides might escape this first quality control. In turn, assembly of heterodimeric molecules as well as mutant homodimers would result in activities closer to 1:4 of FXI:C normal range.

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

INTRODUCTION: Hereditary factor XI (FXI) deficiency is a rare coagulation disorder that may result in excessive bleeding requiring intervention to restore haemostasis. AIM: The aim of this review was to report the current knowledge of the worldwide incidence and prevalence of FXI deficiency. METHODS: A targeted PubMed search using terms related to FXI deficiency was conducted to identify studies published from April 2002 through April 2022. A manual search supplemented the electronic search. Studies were eligible for data abstraction if they reported population-based incidence proportions/rates or prevalence proportions for FXI deficiency. RESULTS: The electronic and manual searches returned 253 publications. After applying exclusion criteria, seven publications were included in the analysis, including a global report from the World Federation of Haemophilia (WFH). Six publications provided information on the prevalence of FXI deficiency that included 74 countries and regions. The estimated prevalence of FXI in the WFH report ranged from 0/100,000 in several countries to 55.85/100,000 individuals in the United Kingdom. Prevalence estimates in the PubMed findings ranged from .1 to 246.2/1,000,000 inhabitants with varying methods of case identification and time periods of analysis. One study estimated the incidence of FXI deficiency in Yecla, Spain at 2% of blood donors and .09% of hospital inpatients/outpatients with activated partial thromboplastin time (aPTT) tests. CONCLUSION: FXI deficiency is rare across the world, but additional steps could be taken to improve incidence and prevalence estimation, for example, development of a consistent FXI deficiency definition and incorporating genetic testing into a clinical routine to better identify and characterise cases.

Leveraging genetic predictors of factor XI levels to anticipate results from clinical trials.

BACKGROUND: Factor XI (FXI) is a promising therapeutic target for the prevention of thrombotic disease without increasing bleeding risk. METHODS: We performed Mendelian randomization (MR) analyses to investigate the association of genetically predicted reductions in FXI levels with risk of venous thromboembolism, ischemic stroke, bleeding outcomes, and lifespan. RESULTS: Genetically predicted reductions in FXI levels were associated with lower risk of ischemic stroke (odds ratio per 1 standard deviation (SD) lower serum FXI 0.90, 95% confidence interval 0.87-0.93, p = 1.59 × 10-11 ), and venous thromboembolism (0.54, 0.49-0.59, p = 2.13 × 10-39 ) but did not associate with increased bleeding risk (p > 0.16). Genetically predicted reductions in serum FXI levels associated with longer lifespan (0.37 years per 1 SD lower serum FXI, 0.13-0.61, p = 0.003). CONCLUSIONS: These genetic data support FXI as a potentially efficacious and safe therapeutic target and anticipate positive results from ongoing phase 3 clinical trials.

Gene Variants in Two Families with Inherited Coagulation Factor XI Deficiency and Identification of Mutations.

INTRODUCTION: Mutations in the F11 gene can cause factor XI (FXI) deficiency, leading to abnormal coagulation activity and injury-related bleeding tendency. Therefore, identifying F11 gene mutations and studying the molecular basis will help us understand the pathogenesis of FXI deficiency. METHODS: Coagulation tests and gene sequencing analysis of all members were performed. FXI wild-type and mutant expression plasmids were constructed and transfected into HEK293FT cells. The FXI protein expression level was evaluated by ELISA and Western blot. RESULTS: The FXI activity (FXI:C) and FXI antigen (FXI:Ag) of proband-1 were decreased to 2% and 5%, respectively. FXI:C and FXI:Ag of proband-2 were reduced to 15% and 32%, respectively. Four mutations were found in the two unrelated families, including c.536C>T (p.T179M), c.1556G>A (p.W519*), c.434A>G (p.H145R), and c.1325_1325delT (p.L442Cfs*8). In vitro studies in transiently transfected HEK293FT cells demonstrated that p.T179M, p.W519*, and p.L442Cfs*8 mutations significantly lowered the FXI levels in the culture media. The FXI levels in the culture media and cell lysates of p.H145R mutation were similar to the wild type. CONCLUSION: Our results confirm that the four mutations in the F11 gene are causative in the 2 FXI deficiency families. Moreover, the p.H145R mutation is a cross-reactive material (CRM)-positive phenotype. The other three mutations are CRM-negative phenotypes and lead to FXI protein secretion disorder.

Effects of LEF-11 acetylation modification on the regulation of baculovirus infection.

Late expression factor 11 (LEF-11) is an essential protein in the regulation of Bombyx mori nucleopolyhedrovirus (BmNPV) DNA replication and late gene expression. Our recent quantitative analysis of protein acetylome revealed for the first time that LEF-11 can be acetylated at one lysine residue (K83) during viral infection, but the underlying mechanism is unclear. The acetylation level for K83 was down-regulated after 36 h post-infection by approximately 30%. To clarify the regulatory function of this modification, overlap PCR was used for site-specific mutagenesis for acetylated (K83Q) or deacetylated (K83R) mimic mutants of LEF-11. The results of viral titration and quantitative polymerase chain reaction showed that after K83 acetylation, budding virion production and the viral genome replication level were significantly upregulated. Meanwhile, the results of yeast two-hybrid (Y2H) system confirmed that K83 deacetylation modification inhibited the interaction between LEF-11 and immediate early gene 1 (IE-1). In conclusion, the acetylation of LEF-11 at K83 might enhance the interaction with IE-1 in the host cell nucleus to promote viral DNA replication, and might be one of the antiviral strategies of the silkworm host. The host inhibits virus proliferation by deacetylating LEF-11. Keywords: BmNPV; LEF-11; acetylation; virus replication; protein interaction.

[Analysis of a Chinese pedigree affected with Hereditary coagulation factor â ª deficiency due to variant of F11 gene].

OBJECTIVE: To explore the molecular pathogenesis of a Chinese pedigree affected with Hereditary coagulation factor Ⅺ (FⅪ) deficiency due to variants of the F11 gene. METHODS: A male proband with Hereditary coagulation factor Ⅺ deficiency who was admitted to the First Affiliated Hospital of Wenzhou Medical University due to urinary calculi on November 30, 2020 and his family members (7 individuals from 3 generations in total) were selected as the study subjects. Clinical data of the proband were collected, and relevant coagulation indices of the proband and his family members were determined. Genomic DNA of peripheral blood samples was extracted for PCR amplification. All exons, flanking sequences, and 5' and 3' untranslated regions of the F11 gene of the proband were analyzed by direct sequencing. And the corresponding sites were subjected to sequencing in other family members. The conservation of amino acid variation sites was analyzed by bioinformatic software, and the effect of the variant on the protein function was analyzed. Variants were graded based on the guidelines from the American College of Medical Genetics and Genomics (ACMG). RESULTS: The proband was a 36-year-old male. His activated partial thromboplastin time (APTT) was 89.2s, which was significantly prolonged. The FⅪ activity (FⅪ:C) and FⅪ antigen (FⅪ:Ag) were 2.0% and 3.5%, respectively, which were extremely reduced. Both the proband and his sister were found to harbor compound heterozygous variants of the F11 gene, including a c.689G>T (p.Cys230Phe) missense variant in exon 7 from their father and a c.1556G>A (p.Trp519*) nonsense variant in exon 13 from their mother. Conservation analysis indicated the Cys230 site to be highly conserved. The c.1556G>A (p.Trp519*) variant was known to be pathogenic, whilst the c.689G>T variant was classified as likely pathogenic (PM2+PM5+PP1+PP3+PP4) based on the ACMG guidelines. CONCLUSION: The c.689G>T and c.1556G>A compound heterozygous variants of the F11 gene probably underlay the pathogenesis of FⅪ deficiency in this pedigree.

Detection and Gene Mutation Analysis of Three Variations in Two Unrelated Chinese Hereditary Coagulation Factor XI Deficiency Families.

INTRODUCTION: Three variations including a novel F11 gene variation were detected in two unrelated Chinese families with coagulation factor XI deficiency, and their possible pathogenesis was elucidated. METHODS: The genomic DNA of the probands' pedigrees was extracted, and all exons and flanking sequences of F11 gene were subjected to PCR amplification and Sanger sequencing. ClustalX-2.1-win, Mutation Taster, and Swiss-Pdb Viewer software were used to analyze the conservation and impact of the variations on protein function and structure. RESULTS: DNA sequencing showed that the proband one had p.Gly350Glu and p.Trp501stop complex heterozygous variations, while the proband two took p.Pro338Leu and p.Trp501stop compound heterozygous variations. Conservation, structural, and functional analysis of variant amino acids indicated that these three variations were harmful and probably affected the structure and function of the variable protein. CONCLUSIONS: Three variations including p.Pro338Leu, p.Gly350Glu, and p.Trp501stop responsible for the reduction of the FXI activities were herein detected. Notably, the p.Pro338Leu variation was discovered for the first time in the world. Furthermore, the p.Gly350Glu was first reported in China.

[Two cases of coagulation factor â ª deficiency caused by compound heterozygous mutations].

OBJECTIVE: To investigate the molecular pathogenesis of two coagulation factor Ⅺ (FⅪ) deficiency patients. METHODS: Coagulant assays: activated partial thromboplastin time (APTT), normal pooled-plasma corrected APTT test, PT, PT-INR and one-stage assay of coagulation factors activities were validated to diagnose coagulation factor Ⅺ deficiency. The patients' DNA samples were extracted and all exons and flanking sequences of F11 gene were amplified using PCR. After purified, the products of PCR were sequenced directly, the mutations were detected by comparing with wild sequences and analyzed using some bio-informatics softwares. RESULTS: The two patients were diagnosed with coagulation factor Ⅺ deficiency due to prolonged APTT, corrected APTT and low activities of coagulation factor FⅪ. The results of APTT, FⅪ: C were 88.1s, 1.1% and 107.1s, 3.8%, and the prolonged APTT could be corrected to normal range 32.9 s and 31.5 s, respectively. Through genetic analysis, we discovered compound heterozygous mutations g.1305-1G>A and g.1325delT in patient 1 and the sequencing results of TA plasmid clones showed that the two mutations were located on different strands of chromosomes. Compound heterozygous mutations g.1124A>G and g.1550C>G were detected in patient 2 resulting in Lys357Arg and Cys482Trp. Software analysis indicated the mutations probably brought amino acid sequence changed, protein features affected and splice site changed. CONCLUSION: Compound heterozygous mutations g.1305-1G>A, g.1325delT and g.1124A>G, g.1550C>G had been identified in two coagulation factor Ⅺ deficiency patients which might be responsible for their prolonged APTT and low FⅪ: C. To the best of our knowledge, g.1325delT and g.1550C>G have been reported, while g.1124A>G and g.1305-1G>A are reported for the first time in the literature.

[Analysis of hereditary coagulation factor â ª deficiency in a Chinese pedigree with compound heterozygous mutations].

OBJECTIVE: To explore the molecular mechanisms of a Chinese pedigree with hereditary factor Ⅺ (FⅪ) deficiency. METHODS: All of the 15 exons, flanking sequences of the FⅪ gene and the corresponding mutation sites of family members were analyzed by the Sanger sequencing, followed by the extraction of the peripheral blood genomic DNA. And all the results were verified by the reverse sequencing. The conservation of the mutated sites was analyzed by the ClustalX-2.1-win. Three online bioinformatics software tools, including Mutation Taster, PolyPhen2 and the PROVEAN, were used to assess the possible impact of the mutations. Swiss-pdbviewer software was used to analyze the effects of mutant amino acids on protein structure. RESULTS: Genetic analysis revealed that the proband had compound heterozygous mutations including a nonsense mutation of c.1107C>A (Tyr369stop) in exon 10 and missense mutation of c.1562A>G (Tyr521Cys) in exon 13. The same c.1107C>A (Tyr369stop) was present in her father, the same c.1562A>G (Tyr521Cys) was present in both her mother and daughter. Conservation analysis indicated that Tyr521 was a highly conserved site during evolution. The prediction of pathogenicity showed that both c.1107C>A and c.1562A>G were pathogenic mutations. Protein structure prediction showed that in the wild type FⅪ protein structure, Tyr521 formed a hydrogen bond with the Lys572 and Ile388, respectively. When Tyr521 was replaced by Cys521, the original benzene ring structure disappeared, and side chains of Lys572 added a hydrogen bond with the Cys521, which may change protein catalytic domain structure. When Tyr369 was mutated to a stop codon, resulting in the truncated protein. CONCLUSION: The compound heterozygous mutations including the c.1107C>A heterozygous missense variant in exon 10 and the c.1562A>G heterozygous nonsense mutation in exon 13 may be responsible for the hereditary factor Ⅺ deficiency in this Chinese pedigree.

[Analysis of a pedigree affected with hereditary coagulation factor XI deficiency due to compound heterozygous variants of F11 gene].

OBJECTIVE: To analyze the clinical phenotype and genetic basis for a Chinese pedigree affected with coagulation factor XI (FXI) deficiency. METHODS: Activated partial thromboplastin time (APTT) and other blood coagulation factors, and activities of FXI:C and other relevant coagulation factors for a large Chinese pedigree including 6 patients from 3 generations were determined on a Stago automatic coagulometer. The FXI:Ag was determined with an ELISA method. All exons and flanking regions of the F11 gene were subjected to Sanger sequencing. ClustalX-2.1-win software was used to analyze the conservation of amino acids. Pathogenicity of the variants was predicted with online bioinformatics software including Mutation Taster and Swiss-Pdb Viewer. RESULTS: The APTT of the proband was prolonged to 94.2 s. The FXI:C and FXI:Ag were decreased to 1% and 1.3%, respectively. The APTT of her father, mother, son and daughter was 42.1 s, 43.0 s, 42.5 s and 41.0 s, respectively. The FXI:C and FXI:Ag of them were almost halved compared with the normal values. The APTT, FXI:C and FXI:Ag of her husband were all normal. Genetic testing revealed that the proband has carried a heterozygous missense c.1103G>A (p.Gly350Glu) variant in exon 10 and a heterozygous missense c.1556G>A (p.Trp501stop) variant in exon 13 of the F11 gene. The father and daughter were heterozygous for the c.1103G>A variant, whilst the mother and son were heterozygous for the c.1556G>A variant. Both Gly350 and Trp501 are highly conserved among homologous species, and both variants were predicted to be "disease causing" by Mutation Taster. Protein modeling indicated there are two hydrogen bonds between Gly350 and Phe312 in the wild-type, while the p.Gly350Glu variant may add a hydrogen bond to Glu and Tyr351 and create steric resistance between the two, both may affect the structure and stability of protein. CONCLUSION: The c.1103G>A and c.1556G>A compound heterozygous variants probably underlay the pathogenesis of congenital FXI deficiency in this pedigree.

Novel Drug Targets for Ischemic Stroke Identified Through Mendelian Randomization Analysis of the Blood Proteome.

BACKGROUND: Novel, effective, and safe drugs are warranted for treatment of ischemic stroke. Circulating protein biomarkers with causal genetic evidence represent promising drug targets, but no systematic screen of the proteome has been performed. METHODS: First, using Mendelian randomization (MR) analyses, we assessed 653 circulating proteins as possible causal mediators for 3 different subtypes of ischemic stroke: large artery atherosclerosis, cardioembolic stroke, and small artery occlusion. Second, we used MR to assess whether identified biomarkers also affect risk for intracranial bleeding, specifically intracerebral and subarachnoid hemorrhages. Third, we expanded this analysis to 679 diseases to test a broad spectrum of side effects associated with hypothetical therapeutic agents for ischemic stroke that target the identified biomarkers. For all MR analyses, summary-level data from genome-wide association studies (GWAS) were used to ascertain genetic effects on circulating biomarker levels versus disease risk. Biomarker effects were derived by meta-analysis of 5 GWAS (N≤20 509). Disease effects were derived from large GWAS analyses, including MEGASTROKE (N≤322 150) and UK Biobank (N≤408 961) studies. RESULTS: Several biomarkers emerged as causal mediators for ischemic stroke. Causal mediators for cardioembolic stroke included histo-blood group ABO system transferase, coagulation factor XI, scavenger receptor class A5 (SCARA5), and tumor necrosis factor-like weak inducer of apoptosis (TNFSF12). Causal mediators for large artery atherosclerosis included ABO, cluster of differentiation 40, apolipoprotein(a), and matrix metalloproteinase-12. SCARA5 (odds ratio [OR]=0.78; 95% CI, 0.70-0.88; P=1.46×10-5) and TNFSF12 (OR=0.86; 95% CI, 0.81-0.91; P=7.69×10-7) represent novel protective mediators of cardioembolic stroke. TNFSF12 also increased the risk of subarachnoid (OR=1.53; 95% CI, 1.31-1.78; P=3.32×10-8) and intracerebral (OR=1.34; 95% CI, 1.14-1.58; P=4.05×10-4) hemorrhages, whereas SCARA5 decreased the risk of subarachnoid hemorrhage (OR=0.61; 95% CI, 0.47-0.81; P=5.20×10-4). Multiple side effects beyond stroke were identified for 6 of 7 biomarkers, most (75%) of which were beneficial. No adverse side effects were found for coagulation factor XI, apolipoprotein(a), and SCARA5. CONCLUSIONS: Through a systematic MR screen of the circulating proteome, causal roles for 5 established and 2 novel biomarkers for ischemic stroke were identified. Side-effect profiles were characterized to help inform drug target prioritization. In particular, SCARA5 represents a promising target for treatment of cardioembolic stroke, with no predicted adverse side effects.

Combined Congenital Hypodysfibrinogemia and Factor XI Deficiency in a Chinese Family.

Both congenital hypodysfibrinogenemia and factor XI deficiency are rare coagulopathies caused by mutations within the fibrinogen and F11 genes, respectively. To investigate the pathogenesis of combined congenital hypodysfibrinogenemia with factor XI (FXI) deficiency in a Chinese family, coagulation assays, FXI activity (the 1-stage method), fibrinogen activity (the Clauss method), and antigen (prothrombin time [PT]-derived method) were performed. The sequences of fibrinogen genes and F11 were amplified by PCR and analyzed by direct sequencing. The proband as well as his grandmother, father, aunt, and sister showed a low plasma concentration of fibrinogen measured by the Clauss method and a slightly decreased result by the PT-derived method; finally, c.1097A>G in exon 8 of FGG was detected in the pedigree, which caused His340Arg mutation. His grandfather had a slightly prolonged activated partial thromboplastin time (APTT) due to low FXI activity. FXI deficiency was a compound heterozygote inherited with missense mutations of c.434A>G in exon 5 as well as c.1253G>T in exon 11 which caused HGV p.His145Arg and Gly400Val mutations, respectively. The grandfather had no qualitative or quantitative defect in fibrinogen. The proband and his father and aunt had c.434A>G at the exon 5 mutation site and no decrease in FXI activity. His mother had no fibrinogen or F11 gene mutations. Plasma fibrin polymerization was delayed. The proband in our study showed typical changes of congenital hypodysfibrinogemia in the clotting analyses with delayed fibrin polymerization, but although he was a heterozygous carrier of the c.434A>G variant in the F11 gene, he had no decrease in FXI activity and no bleeding tendency, thus questioning the pathogenicity of the identified variant in the F11 gene. To our knowledge, this is the first report of a case of combined hypodysfibrinogenemia and FXI deficiency confirmed by molecular genetic tests.

Determining the association of thrombophilic gene polymorphisms with recurrent pregnancy loss in Iranian women.

OBJECTIVE: Thrombophilia is known to be associated with poor pregnancy outcomes. In this study, three thrombophilic gene polymorphisms, including EPCR (Ser219Gly), F11 (rs4253417) and F7 (323 Ins10) were investigated in an Iranian population of women in order to determine the correlation between thrombophilia and recurrent pregnancy loss (RPL). METHODS: Polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) were used to evaluate the frequency of three candidate thrombophilic risk factors for recurrent pregnancy loss. The frequencies of the polymorphisms were compared between the case (144 patients with a history of at least two miscarriages) and the control (150 healthy women with no abortion) group. RESULTS: Our results show that EPCR and FVII polymorphisms of the patient and control group have the same genotype frequency, and the difference is not statistically significant (p-value > .05). Regarding FXI polymorphism, TT genotype frequency was higher in the patient group than the control group (p-value < .05); however, CT heterozygote form was higher in the control group compared to the patient group (p-value < .05). CONCLUSION: In FXI polymorphism, T allele is possibly an RPL risk factor and C allele has a protective role. Thus, wild type FXI could be related to RPL, but EPCR and FVII polymorphism have no such correlation.

Congenital factor XI deficiency caused by a novel F11 missense variant: a case report.

Hereditary factor XI (FXI) deficiency is a mild bleeding disorder, rare in the general population but relatively common among Ashkenazi Jews. The human F11 gene comprises 15 exons, spanning over 23 kb of the long arm of chromosome 4 (4q35). Homozygotes or compound heterozygotes typically show severe FXI deficiency, whereas heterozygotes show partial or mild deficiency. However, the genotype-phenotype relationship is difficult to establish, even among individuals within the same family. We report on a female patient with a heterozygous variant in F11 and FXI deficiency (49 IU/dL), who suffers from menorrhagia since menarche and easy bruising. She experienced excessive bleeding during thyroidectomy and after a cesarean section. Her younger sister, who carries the same heterozygous variant in F11 and has mild FXI deficiency (47 IU/dL), has menorrhagia without other bleeding difficulties although she has undergone several surgeries. Their father, who carries the same missense variant, has not experienced any bleeding difficulties (but he has not undergone any surgeries either). The family study revealed that the A428C mutation was inherited from the father. This variant has not previously been described in the literature and is the first F11 variant described in the Croatian population. Our study showed that even when family members have the same germline F11 variant, they still may experience phenotypic variability, making disease prognosis more complex.

[Phenotype and Genotype Analysis in Two Pedigrees with Hereditary Coagulation Factor â ª Deficiency].

OBJECTIVE: To analyze the phenotype and genotype in two pedigrees with hereditary coagulation factor Ⅺ (FⅪ) deficiency, and investigate the molecular mechanisms of FⅪ deficiency. METHODS: Two patients with hereditary coagulation FⅪ deficiency were admitted to Chaozhou Central Hospital in Nov 2014 and Jan 2018. The prothrombin time (PT), activated partial thromboplastin time (APTT), FⅪ activity (FⅪ∶C) and FⅪ antigen (FⅪ∶Ag) were tested for phenotypic diagnosis. All the exons and exon-intron boundaries of FⅪ gene of proband were analyzed by PCR and sequencing. The family members were tested for the mutant site of proband. Then the mRNA of FⅪ in the proband was analyzed with RT-PCR. RESULTS: The proband-1 was a 7-year-old boy, PT was 10.7 s and APTT was 97.4 s (reference range: 9-12.8 s; 24-40 s), FⅪ∶C (0.6%) and FⅪ∶Ag<1% (reference range: 65%-150%; 72.1%-122.3%). The proband-2 was a 30-year-old female, and showed the PT (11.7 s), APTT (71.3 s), FⅪ∶C (0.7%) and FⅪ∶Ag<1%. FⅧ∶C, FⅨ∶C and FⅫ∶C of two proband were within the normal range. DNA sequencing showed that the proband-1 had a combined mutation of c.326-1G>A and c.1107C>A (p.Tyr351X) in exon 10. His grandmother, mother and brother had a heterozygous splicing mutation of c.326-1G>A, his grandmother and father had a homozygous mutation of c.1107C>A. FXI mRNA was undetected in the proband-1. The proband-2 had a homozygous mutation of c.841C>T (p.Gln263X) in exon 8, and this mutation was also found in her father, mother, daughter and son. CONCLUSION: The c.326-1G>A, c.1107C>A(p.Tyr351X) and c.841C>T (p.Gln263X) might be the molecular pathogenesis for two probands with hereditary coagulation factor Ⅺ deficiency.

Leveraging Human Genetics to Estimate Clinical Risk Reductions Achievable by Inhibiting Factor XI.

Background and Purpose- Coagulation factor XI (FXI) is a novel target for antithrombotic therapy addressed by various therapeutic modalities currently in clinical development. The expected magnitude of thrombotic event reduction mediated by targeting FXI is unclear. Methods- We analyzed the association of 2 common genetic variants, which alter levels of FXI, with a range of human phenotypes. We combined variants into a genetic score standardized to a 30% increase in relative activated partial thromboplastin time, equivalent to what can be achieved with pharmacological FXI reduction. Using data from 371 695 participants in the United Kingdom Biobank and 2 large-scale genome-wide association studies, we examined the effect of this FXI score on thrombotic and bleeding end points. Results- Genetic disposition to lower FXI levels was associated with reduced risks of venous thrombosis (odds ratio, 95% CI; P value; odds ratio=0.1, 0.07-0.14; P=3×10-43) and ischemic stroke (odds ratio=0.47, 0.36-0.61; P=2×10-8) but not with major bleeding (odds ratio=0.7, 0.45-1.04; P=0.0739). The observed relative risk reductions were consistent within a range of subgroups that were at high risk for thrombosis. Consistently, we observed higher absolute risk reductions conferred by genetically lower FXI levels in high-risk subgroups, such as patients with atrial fibrillation. Conclusions- Human genetic data suggest that pharmacological inhibition of FXI may achieve considerable reductions in ischemic stroke risk without clear evidence for an associated risk of major bleeding. The quantitative framework developed can be used to support the estimation of achievable risk reductions with pharmacological modulation of FXI.