Identification of four novel polymorphisms in the Aalpha and gamma fibrinogen genes and analysis of association with plasma levels of the protein

Investigation on genetic thrombophilic factors in FFPE autopsy tissue from subjects who died from pulmonary embolism

Venous thromboembolism (VTE) is a multifactorial disease determined by a combination of inherited and acquired factors. Inherited factors include mutations in the genes coding for coagulation factors, some of which seem to exert a differential influence on the risk of developing deep vein thrombosis (DVT) and pulmonary embolism (PE). In post-mortem studies of subjects who have died from pulmonary embolism (PE), the analysis of the factors that may have augmented the VTE risk is often limited to acquired factors. This is due to the complexity-and sometimes the unfeasibility-of analyzing genetic factors and to insufficient knowledge of their individual roles in PE development. The present study used formalin-fixed paraffin-embedded (FFPE) tissue to investigate a panel of 12 polymorphisms-the largest ever studied-that affect the VTE risk. Tissue samples came from post-mortem examinations performed by the specialists of the Section of Legal Medicine of the Department of Pathology of Marche's Polytechnic University, and by the specialists of Health Care District Hospital of Imola, on 44 subjects who died from PE in the period 1997-2014. All individuals were found to have at least one mutation affecting the VTE risk. The present study demonstrates that genetic analysis can be performed post-mortem and the results are useful for forensic investigations, especially from MTHFR C677T and PAI-1 4G/5G polymorphisms. Broader studies using the techniques described herein are needed to determine the relative influence of the individual polymorphisms and their interaction in PE deaths.

Fibrinogen Genes and Myocardial Infarction

Objective— Fibrinogen has a role in inflammatory processes and participates in atherosclerotic plaque formation. Despite intensive investigation, there is no clear evidence for a role of variations in the genes coding for the fibrinogen-α, fibrinogen-β, and fibrinogen-γ polypeptide chains in myocardial infarction. We examined the association of haplotypes in the 50-kb fibrinogen gene region with myocardial infarction in 2 large case-control samples.

Methods and Results— Study sample 1 consisted of 3657 patients with myocardial infarction and 1211 control individuals and sample 2 comprised 1392 patients and 1392 controls. Haplotypes were inferred from genotype analyses of tagging single nucleotide polymorphisms dispersed among the fibrinogen genes. The frequencies of these haplotypes were not significantly different between the case and control groups in either sample ( P ≥0.07). In addition, haplotypes specific for individual fibrinogen genes were analyzed. No substantial differences in the frequencies of these haplotypes were observed between the groups ( P ≥0.13). Finally, haplotypes composed of SNPs that exhibited relatively low pairwise allelic associations among each other were examined. The proportions of the haplotypes were not significantly different between cases and controls ( P ≥0.12).

Conclusion— A haplotype analysis did not reveal a link between genetic variations in the fibrinogen gene region and myocardial infarction.

Functional polymorphisms of FGA, encoding alpha fibrinogen, are associated with susceptibility to venous thromboembolism in a Taiwanese population

To determine the genetic risk factors for venous thromboembolism (VTE), this study examined 14 genetic variants from 10 hemostatic genes in 186 Taiwanese VTE patients and the same number of matched controls, which demonstrated FGA (encoding alpha fibrinogen) Thr312Ala polymorphism was the only variant significantly associated with VTE. Nine genetic polymorphisms on the fibrinogen cluster region of chromosome 4q28 were further studied, in which four FGA polymorphisms were found in strong linkage disequilibrium and were significantly associated with VTE by genotype and allele frequency analyses. Haplotype analysis showed significantly different FGA haplotype frequencies between VTE patients and controls with the haplotype F1, containing -1051G, -3A, 312Ala and TaqI duplication alleles, significantly associated with susceptibility to VTE (P = 0.001). Haplotype-pair analysis results also indicated a strong association of the haplotype-pair F1F1 with VTE in various VTE patient subgroups. In vitro functional analysis indicated that FGA -1051G, -3A and TaqI duplication alleles enhanced significantly the transcription level of FGA; however, control subjects with FGA genotypes containing these alleles had no elevated plasma fibrinogen levels. In conclusion, our experimental data indicated that functional genetic variants in FGA are risk factors for VTE in Taiwanese populations. Determination of FGA genotypes will likely contribute to primary prevention of this condition.

Asymptomatic carriership of factor V Leiden and genotypes of the fibrinogen gene cluster

We investigated the role of frequent fibrinogen polymorphisms in venous thromboembolic disease in conjunction with inherited thrombophilia. Two hundred unrelated subjects, all carriers of the factor V R506Q mutation (FV Leiden), were genotyped at the fibrinogen gene cluster. Among these subjects, 100 had experienced previous venous thromboembolism (VTE) and 100 were still asymptomatic for VTE. Significant differences were observed between the groups for the BclI polymorphism (P = 0.004). Scanning, by sequencing the DNA regions flanking the BclI marker, revealed new polymorphisms, a C to T transition and a G to T transversion at 1520 and 3369 base pairs 3' to the beta gene stop codon respectively. These markers showed less association with the clinical phenotype than BclI itself. A combined genotype including 10 markers was more frequent among the asymptomatic subjects (17%) than among patients (3%), and was associated with a reduction in fibrinogen antigen level (2.42 +/- 0.35 vs 2.69 +/- 0.41 g/l, P = 0.028) among the asymptomatic subjects. Our data suggest that, in the presence of inherited thrombophilia, frequent fibrinogen polymorphisms may interact to modulate the risk of venous thromboembolism.

Combined segregation and linkage analysis of fibrinogen variability in Israeli families: evidence for two quantitative-trait loci, one of which is linked to a functional variant (-58G > A) in the promoter of the alpha-fibrinogen gene

The association of alpha- and beta-fibrinogen polymorphisms with plasma fibrinogen levels was examined in a sample of 452 family members from 80 Israeli kindreds. The measured genotype analysis indicated that the beta-fibrinogen -455G > A polymorphism was not associated with fibrinogen levels, while the alpha-fibrinogen -58G > A locus showed a significant association with fibrinogen levels (chi2= 17.7; df = 3; p < 0.001), with the -58A allele being associated with higher levels. Segregation analysis in this sample suggested a recessive quantitative-trait locus (QTL) with a major effect that controlled the sex- and age-adjusted fibrinogen levels. Results from a combined segregation/linkage analysis indicated that a single QTL influencing plasma fibrinogen is in gametic equilibrium with the beta-fibrinogen -455G > A and alpha-fibrinogen -58G > A polymorphisms. An extended analysis with a two-QTL model significantly improved the fit of the model (p < or = 0.001), and gave support for linkage between the fibrinogen QTL and the alpha-fibrinogen polymorphism. In vitro analysis with a DNA fragment containing this variant, linked to a reporter gene, showed 2-fold higher expression of the A allele compared to the G allele in the liver cell line HepG2, both under basal conditions and after stimulation with interleukin 6. These results demonstrate that two QTLs are jointly involved in determining plasma fibrinogen levels in this sample of families, one of which is located close to a functional variant in the alpha-fibrinogen locus.

Congenital afibrinogenemia: mutations leading to premature termination codons in fibrinogen A alpha-chain gene are not associated with the decay of the mutant mRNAs

Congenital afibrinogenemia is a rare coagulation disorder with autosomal recessive inheritance, characterized by the complete absence or extremely reduced levels of fibrinogen in patients' plasma and platelets. Eight afibrinogenemic probands, with very low plasma levels of immunoreactive fibrinogen were studied. Sequencing of the fibrinogen gene cluster of each proband disclosed 4 novel point mutations (1914C>G, 1193G>T, 1215delT, and 3075C>T) and 1 already reported (3192C>T). All mutations, localized within the first 4 exons of the A alpha-chain gene, were null mutations predicted to produce severely truncated A alpha-chains because of the presence of premature termination codons. Since premature termination codons are frequently known to affect the metabolism of the corresponding messenger RNAs (mRNAs), the degree of stability of each mutant mRNA was investigated. Cotransfection experiments with plasmids expressing the wild type and each of the mutant A alpha-chains, followed by RNA extraction and semiquantitative reverse-transcriptase-polymerase chain reaction analysis, demonstrated that all the identified null mutations escaped nonsense-mediated mRNA decay. Moreover, ex vivo analysis at the protein level demonstrated that the presence of each mutation was sufficient to abolish fibrinogen secretion.