Fibrinogen Locus Research Articles

FGL1 as a modulator of plasma D‐dimer levels: Exome‐wide marker analysis of plasma tPA, PAI‐1, and D‐dimer

BackgroundUse of targeted exome‐arrays with common, rare variants and functionally enriched variation has led to discovery of new genes contributing to population variation in risk factors. Plasminogen activator‐inhibitor 1 (PAI‐1), tissue plasminogen activator (tPA), and the plasma product D‐dimer are important components of the fibrinolytic system. There have been few large‐scale genome‐wide or exome‐wide studies of PAI‐1, tPA, and D‐dimer. ObjectivesWe sought to discover new genetic loci contributing to variation in these traits using an exome‐array approach. MethodsCohort‐level analyses and fixed effects meta‐analyses of PAI‐1 (n = 15 603), tPA (n = 6876,) and D‐dimer (n = 19 306) from 12 cohorts of European ancestry with diverse study design were conducted, including single‐variant analyses and gene‐based burden testing. ResultsFive variants located in NME7, FGL1, and the fibrinogen locus, all associated with D‐dimer levels, achieved genome‐wide significance (P < 5 × 10−8). Replication was sought for these 5 variants, as well as 45 well‐imputed variants with P < 1 × 10−4 in the discovery using an independent cohort. Replication was observed for three out of the five significant associations, including a novel and uncommon (0.013 allele frequency) coding variant p.Trp256Leu in FGL1 (fibrinogen‐like‐1) with increased plasma D‐dimer levels. Additionally, a candidate‐gene approach revealed a suggestive association for a coding variant (rs143202684‐C) in SERPINB2, and suggestive associations with consistent effect in the replication analysis include an intronic variant (rs11057830‐A) in SCARB1 associated with increased D‐dimer levels. ConclusionThis work provides new evidence for a role of FGL1 in hemostasis.

Fibrinogen in equine pregnancy as a mediator of cell adhesion, an epigenetic and functional investigation.

Preimplantation equine embryos synthesize and secrete fibrinogen, which is a peculiar finding as fibrinogen synthesis almost exclusively occurs in the liver. This study investigated the hypothesis that conceptus-derived fibrinogen mediates cell adhesion during fixation. On day 21 of pregnancy, five integrin subunits, including ITGA5, ITGB1, ITGAV, and ITGB1, displayed significantly higher transcript abundance than on day 16 of pregnancy. Endometrial epithelial cells adhered to fibrinogen in an integrin-dependent manner in an in vitro cell adhesion assay. Bilaminar trophoblast and allantochorion expressed fibrinogen transcript, indicating that fibrinogen expression persists past fixation. Preimplantation-phase endometrium, conceptuses, and microcotyledonary tissue expressed components of the clotting cascade regulating fibrin homeostasis, leaving open the possibility that fibrinogen is converted to fibrin. Fibrinogen is likely to have functions beyond mediating cell adhesion, such trapping growth factors and triggering signaling cascades, and has remarkable parallels to the expression of fibrinogen by some tumors. The deposition of fibrinogen within tumor stroma is characteristic of breast carcinoma, and tumor-derived fibrinogen has been implicated in the metastatic potential of circulating tumor cells. DNA methylation of the fibrinogen locus in equine conceptuses was examined in comparison to liver and endometrium, and across the full gene cluster, was significantly higher for endometrium than liver and conceptus. DNA methylation of regulatory regions did not differ between liver and conceptus, and was significantly lower than in endometrium. These results, therefore, support the hypothesis of DNA methylation being a regulator of fibrinogen expression in the conceptus.

Local chromatin interactions contribute to expression of the fibrinogen gene cluster

Background The coordinately regulated genes encoding human fibrinogen are clustered. This evolutionarily conserved configuration provides a possible mechanism for co-regulation whereby regulatory elements influence gene expression locally. The cluster is flanked by CCCTC-binding factor (CTCF) interaction sites that are candidate insulator regions mediating chromatin looping. Objectives To further our understanding of fibrinogen gene regulation, we aimed to investigate whether interactions exist between parts of the fibrinogen locus and how these contacts contribute to fibrinogen expression. Methods We used chromosome conformation capture in cultured cell lines to detect chromatin interactions at the fibrinogen gene cluster. We generated clonal cell lines where two CTCF interaction sites at one end of the locus were deleted using CRISPR-Cas9-mediated genome editing. Fibrinogen expression and protein production were measured using qRT-PCR and ELISA, respectively. Results We detected proximity between the ends of the fibrinogen locus, regardless of whether cells express fibrinogen. An interaction between the FGA promoter and the edge of the locus was more frequent in fibrinogen-expressing cells. Deletion of a CTCF site at one edge of the cluster altered chromatin interactions, reduced steady-state expression of FGB and FGG mRNA, and led to a halving of secreted fibrinogen. These phenotypes were completely restored by reintroduction of the CTCF interaction motif in previously motif-deleted clones. Conclusions Chromatin interactions are important for the coordinated regulation of the human fibrinogen genes. This finding furthers our comprehension of how fibrinogen is produced and identifies a possible source of variability in plasma fibrinogen levels seen in populations.

DNA Methylation Profiling of the Fibrinogen Gene Landscape in Human Cells and during Mouse and Zebrafish Development

The fibrinogen genes FGA, FGB and FGG show coordinated expression in hepatocytes. Understanding the underlying transcriptional regulation may elucidate how their tissue-specific expression is maintained and explain the high variability in fibrinogen blood levels. DNA methylation of CpG-poor gene promoters is dynamic with low methylation correlating with tissue-specific gene expression but its direct effect on gene regulation as well as implications of non-promoter CpG methylation are not clear. Here we compared methylation of CpG sites throughout the fibrinogen gene cluster in human cells and mouse and zebrafish tissues. We observed low DNA methylation of the CpG-poor fibrinogen promoters and of additional regulatory elements (the liver enhancers CNC12 and PFE2) in fibrinogen-expressing samples. In a gene reporter assay, CpG-methylation in the FGA promoter reduced promoter activity, suggesting a repressive function for DNA methylation in the fibrinogen locus. In mouse and zebrafish livers we measured reductions in DNA methylation around fibrinogen genes during development that were preceded by increased fibrinogen expression and tri-methylation of Histone3 lysine4 (H3K4me3) in fibrinogen promoters. Our data support a model where changes in hepatic transcription factor expression and histone modification provide the switch for increased fibrinogen gene expression in the developing liver which is followed by reduction of CpG methylation.

Fibrinogen gene regulation

The Aα, Bβ and γ polypeptide chains of fibrinogen are encoded by a three gene cluster on human chromosome four. The fibrinogen genes (FGB-FGA-FGG) are expressed almost exclusively in hepatocytes where their output is coordinated to ensure a sufficient mRNA pool for each chain and maintain an abundant plasma fibrinogen protein level. Fibrinogen gene expression is controlled by the activity of proximal promoters which contain binding sites for hepatocyte transcription factors, including proteins which influence fibrinogen transcription in response to acute-phase inflammatory stimuli. The fibrinogen gene cluster also contains cis regulatory elements; enhancer sequences with liver activities identified by sequence conservation and functional genomics. While the transcriptional control of this gene cluster is fascinating biology, the medical impetus to understand fibrinogen gene regulation stems from the association of cardiovascular disease risk with high level circulating fibrinogen. In the general population this level varies from about 1.5 to 3.5 g/l. This variation between individuals is influenced by genotype, suggesting there are genetic variants contributing to fibrinogen levels which reside in fibrinogen regulatory loci. A complete picture of how fibrinogen genes are regulated will therefore point towards novel sources of regulatory variants. In this review we discuss regulation of the fibrinogen genes from proximal promoters and enhancers, the influence of acute-phase stimulation, post-transcriptional regulation by miRNAs and functional regulatory variants identified in genetic studies. Finally, we discuss the fibrinogen locus in light of recent advances in understanding chromosomal architecture and suggest future directions for researching the mechanisms that control fibrinogen expression.

A liver enhancer in the fibrinogen gene cluster

AbstractThe plasma concentration of fibrinogen varies in the healthy human population between 1.5 and 3.5 g/L. Understanding the basis of this variability has clinical importance because elevated fibrinogen levels are associated with increased cardiovascular disease risk. To identify novel regulatory elements involved in the control of fibrinogen expression, we used sequence conservation and in silico–predicted regulatory potential to select 14 conserved noncoding sequences (CNCs) within the conserved block of synteny containing the fibrinogen locus. The regulatory potential of each CNC was tested in vitro using a luciferase reporter gene assay in fibrinogen-expressing hepatoma cell lines (HuH7 and HepG2). 4 potential enhancers were tested for their ability to direct enhanced green fluorescent protein expression in zebrafish embryos. CNC12, a sequence equidistant from the human fibrinogen alpha and beta chain genes, activates strong liver enhanced green fluorescent protein expression in injected embryos and their transgenic progeny. A transgenic assay in embryonic day 14.5 mouse embryos confirmed the ability of CNC12 to activate transcription in the liver. While additional experiments are necessary to prove the role of CNC12 in the regulation of fibrinogen, our study reveals a novel regulatory element in the fibrinogen locus that is active in the liver and may contribute to variable fibrinogen expression in humans.

Association of genomic loci from a cardiovascular gene SNP array with fibrinogen levels in European Americans and African-Americans from six cohort studies: the Candidate Gene Association Resource (CARe)

AbstractSeveral common genomic loci, involving various immunity- and metabolism-related genes, have been associated with plasma fibrinogen in European Americans (EAs). The genetic determinants of fibrinogen in African Americans (AAs) are poorly characterized. Using a vascular gene-centric array in 23 634 EA and 6657 AA participants from 6 studies comprising the Candidate Gene Association Resource project, we examined the association of 47 539 common and lower frequency variants with fibrinogen concentration. We identified a rare Pro265Leu variant in FGB (rs6054) associated with lower fibrinogen. Common fibrinogen gene single nucleotide polymorphisms (FGB rs1800787 and FGG rs2066861) significantly associated with fibrinogen in EAs were prevalent in AAs and showed consistent associations. Several fibrinogen locus single nucleotide polymorphism associated with lower fibrinogen were exclusive to AAs; these include a newly reported association with FGA rs10050257. For IL6R, IL1RN, and NLRP3 inflammatory gene loci, associations with fibrinogen were concordant between EAs and AAs, but not at other loci (CPS1, PCCB, and SCL22A5-IRF1). The association of FGG rs2066861 with fibrinogen differed according to assay type used to measure fibrinogen. Further characterization of common and lower-frequency genetic variants that contribute to interpopulation differences in fibrinogen phenotype may help refine our understanding of the contribution of hemostasis and inflammation to atherothrombotic risk.

Evidence for a quantitative trait locus for plasma fibrinogen from a family–based association study

AbstractStudies in unrelated individuals have shown an association between fibrinogen gene polymorphisms and plasma fibrinogen levels, which is itself a risk factor for coronary heart disease. Family‐based studies have complementary strengths in the investigation of such hypothesized genetic associations. Genotypes at the β‐fibrinogen ‐455G/A promoter polymorphism, and a neighbouring highly polymorphic microsatellite in the α‐fibrinogen gene were examined for evidence of genetic linkage and association with plasma fibrinogen in 568 members of 97 Caucasian families. The heritability of plasma fibrinogen was 0.22 ± 0.08, P = 0.0007. There was no significant evidence of genetic linkage between the fibrinogen locus and plasma fibrinogen with either marker. In contrast, there was evidence for association of plasma fibrinogen with genotype at the β‐455G/A polymorphism (χ12 = 11.12; P = 0.0009). Tests examining allelic transmission from heterozygous parents confirmed this association (Monk’s test, T = 2.17; P = 0.03). Genotype at the β‐455G/A polymorphism accounted for 2% of the observed variation in fibrinogen. This is equivalent to about 10% of the heritable component, suggesting the presence of other quantitative trait loci (QTL) in unlinked genes. Confirmation of the association of plasma fibrinogen with genotype at the β‐455G/A polymorphism in families indicates that the association is due to the physical proximity of this marker to a QTL, although the effect of this QTL was too small to be detected by linkage in this study. These findings are of potential importance for the design of genetic studies of multifactorial quantitative traits.

A Novel Transgenic Mouse Model of Hyperfibrinogenemia

Hyperfibrinogenemia is a risk predictor in several diseases, including cardiovascular disease. Nevertheless, it remains unknown whether elevated fibrinogen has an etiologic role in or is a reflection of disease pathogenesis, or both. To examine this question, we generated a mouse model of hyperfibrinogenemia. We isolated the mouse fibrinogen locus, containing the three fibrinogen genes, in a single P1 clone. This approximately 100 kb clone was injected into C57Bl/6J zygotes. Three transgenic lines were identified, two with elevated fibrinogen, 1.4- and 1.7-fold relative to normal. We characterized the line with the higher level. Northern blots of total RNA showed transgene expression was liver specific, and the message levels were 2- to 3-fold enhanced. Fibrinogen in transgenic mice was normal in both immunologic and clotting assays. Our data indicate that over-expression of all three fibrinogen genes is necessary to achieve hyperfibrinogenemia. We saw no increase in mortality or morbidity, no gross abnormalities in the organs, and no histologic differences in lung, liver, spleen or kidney, in transgenic mice relative to normal littermates. We conclude that elevated fibrinogen did not cause disease in mice. We anticipate that breeding these mice to other mouse models of disease will demonstrate whether hyperfibrinogenemia has a role in the initiation or progression of symptomatic disease.

The 11 kb FGA deletion responsible for congenital afibrinogenaemia is mediated by a short direct repeat in the fibrinogen gene cluster.

Congenital afibrinogenaemia is an autosomal recessive disorder characterised by the complete absence of detectable fibrinogen. We previously identified the first known causative mutations for this disorder in a non-consanguineous Swiss family. The four affected male individuals (two brothers and their first two cousins) were shown to have homozygous deletions of approximately 11 kb of the fibrinogen alpha chain (FGA) gene. Haplotype data suggested that the deletions occurred on three distinct ancestral chromosomes, implying that the FGA region of the fibrinogen locus is susceptible to deletion by a common mechanism, but the sequences responsible for the recombination remained to be identified. Here, we report the detailed characterisation of the deletion by nucleotide sequence analysis of all three deletion junctions and comparison with normal sequences. We found that all three deletions were identical to the base-pair and probably resulted from non-homologous (illegitimate) recombination. The centromeric and telomeric deletion junctions featured both a 7 bp direct repeat, AACTTTT, situated in FGA intron 1 and in the FGA-FGB intergenic sequence and a number of inverted repeats which could be involved in the generation of secondary structures. Analysis with closely linked flanking polymorphic markers revealed the existence of at least two haplotypes, further suggesting independent origins of the deletions in this family.

Deletion of the fibrinogen [correction of fibrogen] alpha-chain gene (FGA) causes congenital afibrogenemia.

Congenital afibrinogenemia is a rare autosomal recessive disorder characterized by the complete absence of detectable fibrinogen. Uncontrolled bleeding after birth from the umbilical cord is common, and spontaneous intracerebral bleeding and splenic rupture can occur throughout life. Patients respond well to fibrinogen replacement therapy, either prophylactically or on demand. Because the half-life of infused fibrinogen is essentially normal, the genetic defect is assumed to be at the level of synthesis, but no responsible locus has been identified. Preliminary studies using Southern blotting suggested that no gross structural changes of the fibrinogen genes were present in patients. We report the identification of causative mutations in a nonconsanguineous Swiss family with congenital afibrinogenemia. The four affected male individuals (two brothers and their two first cousins) have homozygous deletions of approximately 11 kb of the fibrinogen alpha-chain gene (FGA). Haplotype data suggest that these deletions occurred separately, on three distinct ancestral chromosomes, implying that the FGA region of the fibrinogen locus is susceptible to deletion by a common mechanism. Furthermore, our results demonstrate that humans, like mice, may be born without the capacity to synthesize functional fibrinogen.

Structural variation in the alleles of a short tandem repeat system at the human alpha fibrinogen locus.

This paper reports the sequences of 22 alleles identified at the HumFGA (human alpha fibrinogen) short tandem repeat locus in the British Caucasian and Afro-Caribbean populations. Alleles at the lower end of the observed size range were found to increase in size by 4-bp increments with the repeat unit following the pattern TC(TCTT)n. However, 5 alleles were identified that differed in size by 2 bp from the 4 bp increment as a result of the deletion of a TC dinucleotide, or the addition of a TT dinucleotide, immediately prior to the 1st repeat unit. Alleles at the upper end of the observed size range were found to have a more complex repeat unit structure and also exhibited duplication of both 5' and 3' flanking sequences. A nomenclature for the designation of HumFGA alleles is proposed on the basis of this sequence data.

European Atherosclerosis Research Study: Genotype at the Fibrinogen Locus (G−455-A β-Gene) Is Associated With Differences in Plasma Fibrinogen Levels in Young Men and Women From Different Regions in Europe

The European Atherosclerosis Research Study (EARS) compares genetic and environmental factors in the offspring of fathers with myocardial infarction before the age of 55 years (designated cases) and control subjects from five different regions of Europe. Genotype was determined for a G-A polymorphism 455 bp upstream from the start of transcription of the beta-fibrinogen gene. In 585 cases and 1106 control subjects, the relative frequency of the A allele was similar (0.223 and 0.217, respectively), with small and nonsignificant differences in frequency observed among the five regions. Because of evidence for an interaction between a number of factors and genotype in the determination of plasma fibrinogen levels (in particular among female cases who reported use of oral contraceptives), the data were analyzed without adjusting for covariates except for age and region, and analyses were carried out excluding women taking oral contraceptives (n = 297). In agreement with previous reports, in all regions the A allele was associated with elevated plasma fibrinogen levels, with the strongest and most consistent effects being seen in men. In nonsmokers, after adjusting for the effects of age and region, male cases and control subjects with genotype A/A had mean fibrinogen levels 0.49 and 0.33 g/L higher, respectively, than those with genotype G/G, whereas those with genotype G/A had intermediate levels (P < .01). In female nonsmokers there was a similar but smaller and nonsignificant effect (A/A levels higher than G/G by 0.12 and 0.07 g/L, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Linkage disequilibrium relationships among four polymorphisms within the human fibrinogen gene cluster.

The extent of linkage equilibrium was estimated among four recently characterized human fibrinogen restriction fragment length polymorphisms (RFLPs) using a randomly selected group of 110 individuals from California. Two coding region RFLPs, RsaI and MnlI (FGA codon 312 and FGB codon 448, respectively), and two RFLPs located in the 5' flanking region of the FGB gene, AluI (HindIII) and HaeIII, were analyzed. Maximum likelihood estimates based on genotypic data indicated that the RsaI polymorphism in the FGA gene was at apparent linkage equilibrium with the MnlI, AluI, and HaeIII sites in the FGB gene, but strong linkage disequilibrium was noted for the MnlI-AluI, MnlI-HaeIII, and AluI-HaeIII RFLP pairs within the latter gene. The discrepancy in disequilibrium relationships among these closely linked RFLPs may indicate a region of increased recombination between the FGA and FGB RFLP loci. The FGA RsaI polymorphism, when used in conjunction with any of the FGB sites examined, will provide more detailed linkage or association data than analyses that would utilize only FGB sites. Effective use of polymorphisms within the fibrinogen locus will aid analysis of the relationships between fibrinogen genotype, plasma fibrinogen levels, and risk of cardiovascular disease.

Linkage disequilibrium across the fibrinogen locus as shown by five genetic polymorphisms, G/A-455 (HaeIII), C/T-148 (HindIII/AluI), T/G+1689 (AvaII), and BclI (beta-fibrinogen) and TaqI (alpha-fibrinogen), and their detection by PCR.

Human MutationVolume 3, Issue 1 p. 79-81 Mutation in Brief Linkage disequilibrium across the fibrinogen locus as shown by five genetic polymorphisms, G/A −455 (HaeIII), C/T −148 (HindIII/AluI), T/G+1689 (AvaII), and BclI (β-fibrinogen) and TaqI (α-fibrinogen), and their detection by PCR Angela Thomas, Corresponding Author Angela Thomas Division of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandDivision of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandSearch for more papers by this authorHanan Lamlum, Hanan Lamlum Division of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandSearch for more papers by this authorSteve Humphries, Steve Humphries Division of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandSearch for more papers by this authorFiona Green, Fiona Green Division of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandSearch for more papers by this author Angela Thomas, Corresponding Author Angela Thomas Division of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandDivision of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandSearch for more papers by this authorHanan Lamlum, Hanan Lamlum Division of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandSearch for more papers by this authorSteve Humphries, Steve Humphries Division of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandSearch for more papers by this authorFiona Green, Fiona Green Division of Cardiovascular Genetics, Department of Medicine, UniversityCollege London Medical School, The Rayne Institute, London WCIE 6JJ, EnglandSearch for more papers by this author First published: 1994 https://doi.org/10.1002/humu.1380030117Citations: 63AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume3, Issue11994Pages 79-81 RelatedInformation

Fibrinogen genotype and risk of peripheral atherosclerosis

There is conflicting evidence about the influence of fibrinogen genotype on plasma fibrinogen concentrations, and the relation between genotype and atherosclerotic disease has not been studied. In a population-based case-control study we aimed to find out whether certain fibrinogen genotypes are associated with an increased risk of peripheral atherosclerosis. 121 subjects with peripheral arterial disease and 126 healthy controls matched for age and sex were selected from a random population sample aged 55-74 years in the Edinburgh Artery Study. Mean fibrinogen concentrations were higher in cases than in controls (3·12 [95% confidence interval 2·99- 3·26] vs 2·75 [2·64-2·85], p<0·001). A greater proportion of cases than controls were homozygous or heterozygous for an allele at the β fibrinogen locus (4·2 kb allele, Bcl I digestion); the allele frequency was 0·197 in cases and 0·097 in controls (p<0·005). Extended haplotypes for 4·2 kb heterozygotes were also associated with an increased risk of peripheral arterial disease. However, haplotype had only a small effect on the association of plasma fibrinogen concentration with disease, and the relation of haplotype with disease was independent of age, sex, social class, smoking status, plasma fibrinogen, alcohol consumption, body mass index, and diabetes mellitus. We conclude that variation at the β fibrinogen locus is associated with an increased risk of peripheral atherosclerosis. The influence is not mediated simply by way of increased fibrinogen concentrations but could be due to a structurally variant fibrinogen or linkage disequilibrium with a neighbouring gene.

Variation in the Promoter Region of the β Fibrinogen Gene Is Associated with Plasma Fibrinogen Levels in Smokers and Non-Smokers

We investigated the association between fibrinogen levels and a HaeIII restriction fragment length polymorphism located at -453 bp from the start of transcription of the beta fibrinogen gene. 292 healthy men aged 45 to 69 years, recruited from general practices throughout Britain, were studied. None had a history of ischaemic heart disease. 41.1% (120) were smokers and fibrinogen levels were higher in this group. The frequency of the non-cutting allele (designated H2) was 0.19 and was the same in smokers and non-smokers. The H2 allele was associated with elevated levels of fibrinogen in both smokers and non-smokers and the effect of genotype was similar in both groups. After smoking, HaeIII genotype was the strongest predictor of fibrinogen levels and explained 3.1% of the variance in fibrinogen levels. These results confirm earlier studies that variation at the fibrinogen locus contributes to the between-individual differences in plasma fibrinogen level.

Genetic variation at the fibrinogen locus is involved in determining fibrinogen levels: evidence from thirteen individuals sampled on repeated occasions

Genetic variation at the fibrinogen locus is involved in determining fibrinogen levels: evidence from thirteen individuals sampled on repeated occasions

Characterization of the 5'-flanking region for the human fibrinogen beta gene.

To identify the possible regulatory sequences in the genetic expression of fibrinogen, a human genomic DNA library raised in lambda EMBL 4 phage was screened using cDNA probes coding for the A alpha, B beta and gamma chains of human fibrinogen. The entire fibrinogen locus was characterized and its organization analysed by means of hybridization and restriction mapping. Among the clones identified, a single recombinant lambda phage contained the beta gene and its 5'- and 3'-flanking regions. A 1.5 kb fragment of the immediate 5'-flanking region was sequenced and S1 mapping experiments revealed three transcription start points. Comparison of this sequence with that previously reported for the same region upstream from the human gamma gene revealed no significant homology which suggests that the potential promoting sequences of these genes are different. In contrast, comparison of the 5'-flanking regions of human and rat beta genes revealed a 142 bp sequence of 80% homology situated 16 bp upstream from the human beta gene. This highly conserved region may well represents a potential candidate for a regulatory sequence of the human beta gene.