Clinical Consequences and Molecular Bases of Low Fibrinogen Levels

Heat stress-induced platelet dysfunction is associated with loss of fibrinogen and is improved by fibrinogen supplementation

INTRODUCTION

Heatstroke is a critical heat-related condition characterized by coagulopathy and multiple organ dysfunction. One of the most severe complications of heatstroke is disseminated intravascular coagulation. This condition manifests as excessive clot formation and bleeding that are primarily due to platelet depletion and dysfunction. Fibrinogen plays a crucial role in hemostasis because it links integrin αIIbβ3 on adjacent platelets, thereby promoting the platelet activation and aggregation necessary for clot formation. However, reduced fibrinogen levels may impair the formation of the initial platelet plug and increase the risk of bleeding. The current study explored the effect of fibrinogen on platelet dysfunction in a heatstroke model.

MATERIALS AND METHODS

Male Wistar rats were subjected to heat stress, and subsequent changes in hemodynamic, biochemical, and coagulation parameters were analyzed. Platelet viability, aggregation, adhesion, spreading and fibrin clot retraction were assessed.

RESULTS

The rats with heatstroke exhibited a variety of clinical symptoms, including hypotension, tachycardia, multiple organ dysfunction, and coagulopathy. Platelet viability in the heatstroke group was comparable to that in the healthy control group. However, the heatstroke group exhibited significant reductions in plasma fibrinogen levels and platelet aggregation, adhesion, spreading, and fibrin clot retraction. Notably, fibrinogen supplementation markedly augmented the aggregation responses of platelets in the heatstroke group. The impairment of platelet adhesion, spreading, and fibrin clot retraction in the rats with heatstroke was partially ameliorated by fibrinogen supplementation.

CONCLUSIONS

An early use of fibrinogen replacement may serve as a therapeutic intervention to alleviate platelet hyporeactivity and prevent the complications in patients with heatstroke.

The inverted U-shaped association between blood fibrinogen and rehospitalization risk in patients with heart failure

Fibrinogen, a biomarker of thrombosis and inflammation, is related to a high risk for cardiovascular diseases. However, studies on the prognostic value of blood fibrinogen concentrations for heart failure (HF) patients are few and controversial. We performed a retrospective analysis among acute or deteriorating chronic HF patients admitted to a hospital in Sichuan, China, between 2016 and 2019, integrating electronic health care records and external outcome data (N = 1532). During 6 months of follow-up, 579 HF patients were readmitted within 6 months, and 46 of them died. Surprisingly, we found an inverted U-shaped association of blood fibrinogen levels with risk of readmission within 6 months but not with risk of death within 6 months. It was found that HF patients had the highest risk for readmission within 6 months after reaching the turning point for blood fibrinogen (2.4 g/L). In HF patients with low fibrinogen levels < 2.4 g/L, elevated fibrinogen concentrations were still significantly associated with a higher risk for readmission within 6 months [OR = 2.3, 95% CI (1.2, 4.6); P = 0.014] after controlling for relevant covariates. There was no significant association between blood fibrinogen and readmission within 6 months [(OR = 1.0, 95% CI (0.9, 1.1); P = 0.675] in HF patients with high fibrinogen (> 2.4 g/L). The effect difference for the two subgroups was significant (P = 0.014). However, we did not observe any association between blood fibrinogen and death within 6 months stratified by the turning point, and the effect difference for the stratification was not significant (P = 0.380). We observed an inverted U-shaped association between blood fibrinogen and rehospitalization risk in HF patients for the first time. Additionally, our results did not support that elevated blood fibrinogen was related to increased death risk after discharge.

Fibrinogen: Structure, abnormalities and laboratory assays

Fibrinogen is the primary precursor protein for the fibrin clot, which is the final target of blood clotting. It is also an acute phase reactant that can vary under physiologic and inflammatory conditions. Disorders in fibrinogen concentration and/or function have been variably linked to the risk of bleeding and/or thrombosis. Fibrinogen assays are commonly used in the management of bleeding as well as the treatment of thrombosis. This chapter examines the structure of fibrinogen, its role in hemostasis as well as in bleeding abnormalities and measurement thereof with respect to clinical management.

Congenital fibrinogen disorders: a retrospective clinical and genetic analysis of the Prospective Rare Bleeding Disorders Database

ABSTRACT

Congenital fibrinogen deficiency (CFD) is a rare bleeding disorder caused by mutations in FGA, FGB, and FGG. We sought to comprehensively characterize patients with CFD using PRO-RBDD (Prospective Rare Bleeding Disorders Database). Clinical phenotypes, laboratory, and genetic features were investigated using retrospective data from the PRO-RBDD. Patients were classified from asymptomatic to grade 3 based on their bleeding severity. In addition, FGA, FGB, and FGG were sequenced to find causative variants. A total of 166 CFD cases from 16 countries were included, of whom 123 (30 afibrinogenemia, 33 hypofibrinogenemia, 55 dysfibrinogenemia, and 5 hypodysfibrinogenemia) were well characterized. Considering the previously established factor activity and antigen level thresholds, bleeding severity was correctly identified in 58% of the cases. The rates of thrombotic events among afibrinogenemic and hypofibrinogenemic patients were relatively similar (11% and 10%, respectively) and surprisingly higher than in dysfibrinogenemic cases. The rate of spontaneous abortions among 68 pregnancies was 31%, including 86% in dysfibrinogenemic women and 14% with hypofibrinogenemia. Eighty-six patients received treatment (69 on-demand and/or 17 on prophylaxis), with fibrinogen concentrates being the most frequently used product. Genetic analysis was available for 91 cases and 41 distinct variants were identified. Hotspot variants (FGG, p.Arg301Cys/His and FGA, p.Arg35Cys/His) were present in 51% of dysfibrinogenemia. Obstetric complications were commonly observed in dysfibrinogenemia. This large multicenter study provided a comprehensive insight into the clinical, laboratory, and genetic history of patients with CFDs. We conclude that bleeding severity grades were in agreement with the established factor activity threshold in nearly half of the cases with quantitative defects.

Development of biosensors for detection of fibrinogen: a review

Fibrinogen as a major inflammation marker and blood coagulation factor has a direct impact on the health of humanity. The variations in fibrinogen content lead to risky conditions such as bleeding and cardiovascular diseases. So, accurate methods for monitoring of this glycoprotein are of high importance. The conventional methods, such as the Clauss method, are time consuming and require highly specialized expert analysts. The development of fast, simple, easy to use, and inexpensive methods is highly desired. In this way, biosensors have gained outstanding attention since they offer means for performing analyses at the points-of-care using self-testing devices, which can be applied outside of clinical laboratories or hospital. This review indicates that different electrochemical and optical sensors have been successfully implemented for the detection of fibrinogen under normal levels of fibrinogen in plasma. The biosensors for the detection of fibrinogen have been designed based on the quartz crystal microbalance, field-effect transistor, electrochemical impedance spectroscopy, amperometry, surface plasmon resonance, localized surface plasmon resonance, and colorimetric techniques. Also, this review demonstrates the utility of the application of nanoparticles in different detection techniques.

Development and Validation of a Prediction Model for Nd:YAG Laser Capsulotomy: A Retrospective Cohort Study of 9768 eyes

INTRODUCTION

Posterior capsular opacification (PCO) is the most common complication of cataract surgery. In this study, we develop a model to quantitatively predict the probability of Nd:YAG laser capsulotomy for vision-threatening PCO to improve the life quality of postoperative patients.

METHODS

A registry analysis of cataract procedures performed between the years 2010 and 2021. Following the screening of 16,802 patients (25,883 eyes), 9768 patients (eyes) were enrolled. The cohort was randomly divided into two groups: training (n = 6838) and validation (n = 2930). To identify relevant risk factors, univariate, multivariate, and Least Absolute Shrinkage and Selection Operator (LASSO) algorithm Cox regression analysis were employed, and a nomogram was created to demonstrate the prediction result.

RESULTS

At 5 years, the overall cumulative incidence of Nd:YAG laser capsulotomy was 12.0% (1169/9768). The following variables were included in the prediction model: sex [hazard ratio (HR) = 1.53, 95% CI 1.32-1.76], age (HR = 0.71, 95% CI 0.56-0.88), intraocular lens (IOL) material (HR = 2.65, 95% CI 2.17-3.24), high myopia (HR = 2.28, 95% CI 1.90-2.75), and fibrinogen (HR = 0.79, 95% CI 0.72-0.88). In the validation cohort, the area under the curve (AUC) of 1-, 3-, and 5-year predictions for Nd:YAG laser capsulotomy were 0.702, 0.691, and 0.688, respectively. For a subgroup of patients with high myopia, the protective effect of hydrophobic IOL disappeared (HR = 0.68, 95% CI 0.51-1.12, P = 0.127).

CONCLUSION

This model could predict the probability of Nd:YAG laser capsulotomy for vision-threatening PCO after cataract surgery by taking into account factors such as age, gender, IOL material, high myopia, and fibrinogen. Meanwhile, implantation of a hydrophobic IOL in individuals with high myopia did not demonstrate a protective impact against vision-threatening PCO.

Etiology and management of hypofibrinogenemia in trauma

PURPOSE OF REVIEW

Fibrin polymerization is essential for stable clot formation in trauma, and hypofibrinogenemia reduces hemostasis in trauma. This review considers fibrinogen biology, the changes that fibrinogen undergoes after major trauma, and current evidence for lab testing and treatment.

RECENT FINDINGS

Fibrinogen is a polypeptide that is converted to fibrin by the action of thrombin. During trauma, fibrinogen levels are consumed and reduce within the first few hours because of consumption, dilution, and fibrinolysis. Fibrinogen levels usually rebound within 48 hours of injury and can contribute to thrombotic events. The Clauss fibrinogen assay is the gold standard test for fibrinogen levels, although viscoelastic hemostatic assays are often used when a lab delay is anticipated. An evidence-based threshold for fibrinogen replacement is not well established in the literature, but expert opinion recommends maintaining a level above 150 mg/dl.

SUMMARY

Hypofibrinogenemia is an important cause of nonanatomic bleeding in trauma. Despite multiple pathologic causes, the cornerstone of treatment remains fibrinogen replacement with cryoprecipitate or fibrinogen concentrates.

Hepatocyte Nuclear Factor-1α Increases Fibrinogen Gene Expression in Liver and Plasma Fibrinogen Concentration in Rats with Experimental Chronic Renal Failure

Chronic kidney disease (CKD) is associated with elevated plasma fibrinogen concentration. However, the underlying molecular mechanism for elevated plasma fibrinogen concentration in CKD patients has not yet been clarified. We recently found that HNF1α was significantly upregulated in the liver of chronic renal failure (CRF) rats, an experimental model of CKD in patients. Given that the promoter region of the fibrinogen gene possesses potential binding sites for HNF1α, we hypothesized that the upregulation of HNF1α can increase fibrinogen gene expression and consequently plasma fibrinogen concentration in the experimental model of CKD. Here, we found the coordinated upregulation of Aα-chain fibrinogen and Hnfα gene expression in the liver and elevated plasma fibrinogen concentrations in CRF rats, compared with pair-fed and control animals. Liver Aα-chain fibrinogen and HNF1α mRNAs levels correlated positively with (a) liver and plasma fibrinogen levels and (b) liver HNF1α protein levels. The positive correlation between (a) liver Aα-chain fibrinogen mRNA level, (b) liver Aα-chain fibrinogen level, and (c) serum markers of renal function suggest that fibrinogen gene transcription is closely related to the progression of kidney disease. Knockdown of Hnfα in the HepG2 cell line by small interfering RNA (siRNA) led to a decrease in fibrinogen mRNA levels. Clofibrate, an anti-lipidemic drug that reduces plasma fibrinogen concentration in humans, decreased both HNF1α and Aα-chain fibrinogen mRNAs levels in (a) the liver of CRF rats and (b) HepG2 cells. The obtained results suggest that (a) an elevated level of liver HNF1α can play an important role in the upregulation of fibrinogen gene expression in the liver of CRF rats, leading to an elevated concentration of plasma fibrinogen, a protein related to the risk of cardiovascular disease in CKD patients, and (b) fibrates can decrease plasma fibrinogen concentration through inhibition of HNF1α gene expression.

Fracture toughness of fibrin gels as a function of protein volume fraction: Mechanical origins

The mechanical stability of blood clots necessary for their functions is provided by fibrin, a fibrous gel. Rupture of clots leads to life-threatening thrombotic embolization, which is little understood. Here, we combine experiments and simulations to determine the toughness of plasma clots as a function of fibrin content and correlate toughness with fibrin network structure characterized by confocal and scanning electron microscopy. We develop fibrin constitutive laws that scale with fibrin concentration and capture the force-stretch response of cracked clot specimens using only a few material parameters. Toughness is calculated from the path-independent J* integral that includes dissipative effects due to fluid flow and uses only the constitutive model and overall stretch at crack propagation as input. We show that internal fluid motion, which is not directly measurable, contributes significantly to clot toughness, with its effect increasing as fibrin content increases, because the reduced gel porosity at higher density results in greater expense of energy in fluid motion. Increasing fibrin content (1→10mg/mL) results in a significant increase in clot toughness (3→15 N/m) in accordance with a power law relation reminiscent of cellular solids and elastomeric gels. These results provide a basis for understanding and predicting the tendency for thrombotic embolization. STATEMENT OF SIGNIFICANCE: Fibrin, a naturally occurring biomaterial, is the major determinant of the structural and mechanical integrity of blood clots. We determined that increasing the fibrin content in clots, as in some thrombi and fibrin-based anti-bleeding sealants, results in an increase in clot toughness. Toughness corresponds to the ability to resist rupturing in the presence of a defect. We couple bulk mechanical testing, microstructural measurements, and finite element modeling to capture the force-stretch response of fibrin clots and compute toughness. We show that increased fibrin content in clots reduces porosity and limits fluid motion and that fluid motion drastically alters the clot toughness. These results provide a fundamental understanding of blood clot rupture and could help in rational design of fibrin-containing biomaterials.

Physiological correction of hereditary mild hypofibrinogenemia during pregnancy

INTRODUCTION

Hereditary hypofibrinogenemia is a rare fibrinogen disorder characterised by decreased levels of fibrinogen. Pregnant women with hypofibrinogenemia are at risk of adverse obstetrical outcomes, depending on the fibrinogen level.

AIM

We investigated how the physiological changes of hemostasis throughout the pregnancy impact the hemostatic balance in a woman with hereditary mild hypofibrinogenemia.

METHODS

Fibrin clot properties were analyzed by turbidimetry and scanning electron microscopy, clot weight and red blood cells retention were measured by whole clot contraction, and in vitro thrombin generation was assessed by calibrated automated thrombogram and ex vivo by TAT.

RESULTS

Throughout the pregnancy, the fibrinogen levels increased reaching normal values in the third trimester (activity 3.1 g/L, antigen 3.2 g/L). In parallel, the fibrin polymerisation increased, the fibrinolysis decreased, the fibrin clot network became denser with thicker fibrin fibers, and the fibrin clot weight and red blood cells retention increased, reaching control's value at the third trimester. Similarly, in vitro and ex vitro thrombin generation increased, reaching maximum values at the delivery.

CONCLUSION

In this case of hereditary mild hypofibrinogenemia we observed a physiological increase of fibrinogen and thrombin generation. Future studies should focus on moderate and severe hypofibrinogenemia, to assess fibrinogen variation and the overall impact of increased TG on the hemostasis balance.

Molecular basis of rare congenital bleeding disorders

Rare bleeding disorders (RBDs), including factor (F) I, FII, FV, FVII, combined FV and FVIII (CF5F8), FXI, FXIII and vitamin-K dependent coagulation factors (VKCF) deficiencies, are a heterogeneous group of hemorrhagic disorder with a variable bleeding tendency. RBDs are due to mutation in underlying coagulation factors genes, except for CF5F8 and VKCF deficiencies. FVII deficiency is the most common RBD with >330 variants in the F7 gene, while only 63 variants have been identified in the F2 gene. Most detected variants in the affected genes are missense (>50% of all RBDs), while large deletions are the rarest, having been reported in FVII, FX, FXI and FXIII deficiencies. Most were located in the catalytic and activated domains of FXI, FX, FXIII and prothrombin deficiencies. Understanding the proper molecular basis of RBDs not only can help achieve a timely and cost-effective diagnosis, but also can help to phenotype properties of the disorders.

In Vivo Effects of Balanced Crystalloid or Gelatine Infusions on Functional Parameters of Coagulation and Fibrinolysis: A Prospective Randomized Crossover Study

Prudent administration of fluids helps restore or maintain hemodynamic stability in the setting of perioperative blood loss. However, fluids may arguably exacerbate the existing coagulopathy. We sought to investigate the influence of balanced crystalloid and synthetic gelatine infusions on coagulation and fibrinolysis in healthy volunteers. This prospective randomized crossover study included 25 males aged 18–30 years. Infusions performed included 20 mL/kg of a balanced crystalloid solution (Optilyte^®) or 20 mL/kg of gelatine 26.500 Da (Geloplasma^®) in a random order over a period of 2 weeks. Laboratory analysis included conventional coagulation parameters and rotational thromboelastometry (ROTEM) assays. We confirmed a decrease in fibrinogen concentration and the number of platelets, and prolongation of PT after infusions. Compared to baseline values, differences in the ROTEM assays’ results after infusions signified the decrease in coagulation factors and fibrinogen concentration, causing impaired fibrin polymerization and clot structure. The ROTEM indicator of clot lysis remained unaffected. In the case of both Optilyte^® and Geloplasma^®, the results suggested relevant dilution. Gelatine disrupted the process of clot formation more than balanced crystalloid. Infusions of both crystalloid and saline-free colloid solutions causing up to 30% blood dilution cause significant dilution of the coagulation factors, platelets, and fibrinogen. However, balanced crystalloid infusion provides less infusion-induced coagulopathy compared to gelatine.

Clinical, biological, and genetic features in an afibrinogenemia patient series in Algeria

Introduction

The incidence of afibrinogenemia had not been previously reported in Algeria. Afibrinogenemia patients are prone to both haemorrhagic and thrombotic complications. Predictive markers of thrombosis in afibrinogenemia patients are not existent.

Aims and methods

Clinical and biological data from 46 afibrinogenemia patients are reported. Biological investigations included routine tests, genetics analysis and thrombin generation.

Results

FGA mutations (four novel and four previously described) and FGB mutations (seven mutations; five novels) were homozygous in all but one family as a result of 28 consanguineous marriages out of 30 discrete families. Incidence of afibrinogenemia in Algeria is at least 3 per million births. Umbilical bleeding was reported in 39/46 cases and was the main discovery circumstance. We also report post trauma or post‐surgery (3/46) bleeding and spontaneous deep vein thrombosis (DVT) in adulthood (1/46), as discovery circumstances. The median age (10.5‐year‐old) of the population reported here explains why there are few hemarthrosis and obstetrical or gynaecological complications in this series. Thrombotic events were reported in seven patients (four spontaneous). Endogenous Thrombin Potential was significantly increased in thrombosis‐prone patients compared to afibrinogenemic patients with and without personal or familial history (1118 vs. 744 and 817 nM IIa × min, respectively).

Conclusion

The incidence of afibrinogenemia in Algeria is the consequence of consanguineous marriage in families carrying private mutations. The thrombin generation test (TGT) could identify, among afibrinogenemic patients, those presenting a thrombotic risk.

Heterogeneity of Genotype–Phenotype in Congenital Hypofibrinogenemia—A Review of Case Reports Associated with Bleeding and Thrombosis

Congenital fibrinogen disorders are diseases associated with a bleeding tendency; however, there are also reports of thrombotic events. Fibrinogen plays a role in the pathogenesis of thrombosis due to altered plasma concentrations or modifications to fibrinogen’s structural properties, which affect clot permeability, resistance to lysis, and its stiffness. Several distinct types of genetic change and pathogenetic mechanism have been described in patients with bleeding and a thrombotic phenotype, including mutations affecting synthesis or processing in three fibrinogen genes. In this paper, we focused on familial hypofibrinogenemia, a rare inherited quantitative fibrinogen disorder characterized by decreased fibrinogen levels with a high phenotypic heterogeneity. To begin, we briefly review the basic information regarding fibrinogen’s structure, its function, and the clinical consequences of low fibrinogen levels. Thereafter, we introduce 15 case reports with various gene mutations derived from the fibrinogen mutation database GFHT (French Study Group on Hemostasis and Thrombosis), which are associated with congenital hypofibrinogenemia with both bleeding and thrombosis. Predicting clinical presentations based on genotype data is difficult. Genotype–phenotype correlations would be of help to better understand the pathologic properties of this rare disease and to provide a valuable tool for the identification of patients who are not only at risk of bleeding, but also at risk of a thrombotic event.

Development of Transient Recombinant Expression and Affinity Chromatography Systems for Human Fibrinogen

Fibrin forms the structural scaffold of blood clots and has great potential for biomaterial applications. Creating recombinant expression systems of fibrinogen, fibrin’s soluble precursor, would advance the ability to construct mutational libraries that would enable structure–function studies of fibrinogen and expand the utility of fibrin as a biomaterial. Despite these needs, recombinant fibrinogen expression systems, thus far, have relied on the time-consuming creation of stable cell lines. Here we present tests of a transient fibrinogen expression system that can rapidly generate yields of 8–12 mg/L using suspension HEK Expi293^TM cells. We report results from two different plasmid systems encoding the fibrinogen cDNAs and two different transfection reagents. In addition, we describe a novel, affinity-based approach to purifying fibrinogen from complex media such as human plasma. We show that using a high-affinity peptide which mimics fibrin’s knob ‘A’ sequence enables the purification of 50–75% of fibrinogen present in plasma. Having robust expression and purification systems of fibrinogen will enable future studies of basic fibrin(ogen) biology, while paving the way for the ubiquitous use of fibrin as a biomaterial.

Structural and Functional Characterization of Four Novel Fibrinogen Mutations in FGB Causing Congenital Fibrinogen Disorder

Congenital fibrinogen disorders are caused by mutations in genes coding for fibrinogen and may lead to various clinical phenotypes. Here, we present a functional and structural analysis of 4 novel variants located in the FGB gene coding for fibrinogen Bβ chain-heterozygous missense BβY416C and BβA68S, homozygous nonsense BβY345*, and heterozygous nonsense BβW403* mutations. The cases were identified by coagulation screening tests and further investigated by various methods. Fibrin polymerization had abnormal development with decreased maximal absorbance in all patients. Plasmin-induced fibrin degradation revealed different lytic phases of BβY416C and BβW403* than those of the control. Fibrinopeptide cleavage measured by reverse phase high pressure liquid chromatography of BβA68S showed impaired release of fibrinopeptide B. Morphological properties, studied through scanning electron microscopy, differed significantly in the fiber thickness of BβY416C, BβA68S, and BβW403*, and in the fiber density of BβY416C and BβW403*. Finally, homology modeling of BβA68S showed that mutation caused negligible alternations in the protein structure. In conclusion, all mutations altered the correct fibrinogen function or structure that led to congenital fibrinogen disorders.

Fibrinogen and Atherosclerotic Cardiovascular Diseases-Review of the Literature and Clinical Studies

Atherosclerotic cardiovascular diseases (ASCVD), including coronary artery disease, cerebrovascular disease, and peripheral arterial disease, represent a significant cause of premature death worldwide. Biomarkers, the evaluation of which would allow the detection of ASCVD at the earliest stage of development, are intensively sought. Moreover, from a clinical point of view, a valuable biomarker should also enable the assessment of the patient’s prognosis. It has been known for many years that the concentration of fibrinogen in plasma increases, inter alia, in patients with ASCVD. On the one hand, an increased plasma fibrinogen concentration may be the cause of the development of atherosclerotic lesions (increased risk of atherothrombosis); on the other hand, it may be a biomarker of ASCVD, as it is an acute phase protein. In addition, a number of genetic polymorphisms and post-translational modifications of fibrinogen were demonstrated that may contribute to the risk of ASCVD. This review summarizes the current data on the importance of fibrinogen as a biomarker of ASCVD, and also presents the relationship between molecular modifications of this protein in the context of ASCVD.

Congenital Afibrinogenemia and Hypofibrinogenemia: Laboratory and Genetic Testing in Rare Bleeding Disorders with Life-Threatening Clinical Manifestations and Challenging Management

Congenital fibrinogen disorders are rare pathologies of the hemostasis, comprising quantitative (afibrinogenemia, hypofibrinogenemia) and qualitative (dysfibrinogenemia and hypodysfibrinogenemia) disorders. The clinical phenotype is highly heterogeneous, being associated with bleeding, thrombosis, or absence of symptoms. Afibrinogenemia and hypofibrinogenemia are the consequence of mutations in the homozygous, heterozygous, or compound heterozygous state in one of three genes encoding the fibrinogen chains, which can affect the synthesis, assembly, intracellular processing, stability, or secretion of fibrinogen. In addition to standard coagulation tests depending on the formation of fibrin, diagnostics also includes global coagulation assays, which are effective in monitoring the management of replacement therapy. Genetic testing is a key point for confirming the clinical diagnosis. The identification of the precise genetic mutations of congenital fibrinogen disorders is of value to permit early testing of other at risk persons and better understand the correlation between clinical phenotype and genotype. Management of patients with afibrinogenemia is particularly challenging since there are no data from evidence-based medicine studies. Fibrinogen concentrate is used to treat bleeding, whereas for the treatment of thrombotic complications, administered low-molecular-weight heparin is most often. This review deals with updated information about afibrinogenemia and hypofibrinogenemia, contributing to the early diagnosis and effective treatment of these disorders.

A novel fibrinogen γ-chain frameshift mutation, p. Cys365Phefs*41, causing hypofibrinogenemia with bleeding phenotype in a Chinese family

Background

Congenital hypofibrinogenemia is a rare bleeding disease that is classified as the quantitative deficient type. In the present study, investigated the relationship between the genotype and phenotype in a family with hypofibrinogenemia.

Methods

The proband was aware of a predisposition to bleeding. Functional analysis was performed for her all family members, including coagulation function tests, thrombus molecular markers, thromboelastography, scanning electron microscopy, DNA sequencing, and high-performance liquid chromatography-mass spectrometry (HPLC-MS). Pathogenicity analysis and protein modeling of mutant amino acids were also performed.

Results

A novel heterozygous mutation in c.1094delG was detected in FGG exon 8, which resulted in p. Cys365Phefs*41 (containing the signal peptide) in the proband and her mother, who showed a corresponding decrease in fibrinogen function and levels. Thromboelastography indicated that the strength of their blood clots decreased and they had an increased risk of bleeding. The proband fibrin network structure was looser than healthy controls, with large pores in the network, which increased the permeability of lytic enzymes. Results of HPLC-MS showed a lack of mutant peptide chain expression in their plasma, indicating that the family had congenital hypofibrinogenemia, with a clinical phenotype that is related to the degree of fibrinogen deficiency. The mutation truncated the γ-peptide chain and destroyed the functional structure of fibrinogen, including the γ352Cys-γ365Cys disulfide bond. The truncated peptide chains may also lead to nonsense-mediated decay.

Conclusions

The mutation induced a structural change at the carboxyl-terminal of the fibrinogen molecule, leading to fibrinogen secretion dysfunction.

Inflammation and its associations with aortic stiffness, coronary artery disease and peripheral artery disease in different ethnic groups: The HELIUS Study

BACKGROUND

evidence shows important ethnic differences in vascular dysfunction rates; however, the mechanisms driving these differences remain unclear. One potential factor is the ethnic differences in the role of inflammation in vascular injury. We tested the hypothesis that low-grade inflammation is unequally associated with vascular dysfunction in different ethnic groups.

METHODS

we included 5698 participants (similar-sized Dutch, African Surinamese, South-Asian Surinamese, Ghanaians, Turkish, and Moroccans) of the HELIUS study (the Netherlands) conducted between 2011 and 2015. Logistic regression was used to examine the associations of Z-score inflammatory biomarker concentration (high sensitivity C-reactive protein [hs-CRP], fibrinogen, and d-dimer) with vascular dysfunction (aortic stiffness, coronary artery disease [CAD], and peripheral artery disease [PAD]), with adjustments for age, sex, smoking (pack-years), BMI, hypertension, HbA1c, total cholesterol, and statin use.

FINDINGS

in the fully adjusted models, higher Z-score hs-CRP was positively associated with CAD in Dutch [OR 1·63, (95% CI 1·21-2·18)] and PAD in South Asians [1·25(1·03-1·53)], respectively. Higher Z-score fibrinogen was positively associated with CAD in African Surinamese [1·28(1·03-1·59)] while higher Z-score d-dimer was positively associated with PAD in Moroccans [1·39(1·01-1·93)]. Higher Z-score hs-CRP [0·71(0·54-0·94)] and fibrinogen [0·75(0·58-0·97)] concentrations were negatively associated with PAD in African Surinamese.

INTERPRETATION

our study shows that inflammatory biomarkers are unequally associated with vascular dysfunction in different ethnic groups. These observations provide opportunities for future studies aimed at assessing the predictive roles of inflammation on vascular disease in different ethnic groups.

Dysfibrinogenemia-Potential Impact of Genotype on Thrombosis or Bleeding

The congenital dysfibrinogenemias, most often associated with bleeding disorders, encompass mutations in the amino-terminal end of fibrinogen α-chain consisting of Gly17-Pro18-Arg19-Val20, known as knob A, which is a critical site for fibrin polymerization. Here we review the studies reporting dysfibrinogenemia due to mutations affecting fibrinogen knob A and identified 29 papers. The number of reports on dysfibrinogenemias related to residues Gly17, Pro18, Arg19, and Val20 is 5, 4, 18, and 2, respectively. Dysfibrinogenemias related to residues Gly17, Pro18, and Val20 are exclusively associated with bleeding tendency. However, the clinical picture associated with dysfibrinogenemia related to residue Arg19 varies, with most patients suffering from bleeding tendencies, but also transitory ischemic attacks and retinal thrombosis may occur. The reason for this variation is unclear. To elaborate the genotype-phenotype associations further, we studied a Danish family with knob A-related dysfibrinogenemia caused by the Aα Arg19Gly (p.Arg19Gly) mutation using whole-exome sequencing and fibrin structure analysis. Our family is the first reported carrying the p.Arg19Gly mutation combined with one or more single nucleotide polymorphisms (SNP)s in FGA, FGB, and/or FGG and increased fibrin fiber thickness and fibrin mass-to-length ratio suffering from pulmonary emboli, suggesting that compound genotypes may contribute to the thrombogenic phenotype of these patients. Our review, accordingly, focuses on significance of SNPs, compound genotypes, and fibrin structure measures affecting the genotype-phenotype associations in fibrinogen knob A mutations.

Clinical and molecular characterization of Iranian patients with congenital fibrinogen disorders

INTRODUCTION

Congenital fibrinogen disorders (CFDs) are caused by mutations in the FGA, FGB and FGG genes and are classified as quantitative and qualitative fibrinogen defects. This study sought to determine the genetic background of CFDs in Iran and to examine the genotype-phenotype correlation.

METHODS

Fourteen patients with a CFD diagnosis were included. Fibrinogen antigen and activity were measured by the immunoturbidimetric and Clauss methods respectively. Gene sequencing was performed following a polymerase chain reaction amplification of fibrinogen's genes. The ISTH Bleeding Assessment Tool was also evaluated for all cases.

RESULTS

Patients were diagnosed with dysfibrinogenemia (n = 10), hypodysfibrinogenemia (n = 2) and afibrinogenemia (n = 2). Seven different mutations located on FGA exon 2 (57 %), exon 4 (7%), exon 5 (7%) and FGG exon 8 (29 %) were identified. In patients with qualitative deficiencies, mutations were including p.Arg38Thr, p.Arg35His, p.Arg35Cys, p.Val145Asp, and p.Arg301Cys and were including p.Gly316GlufsX105 and p.Trp52stop in afibrinogenemic patients. In dysfibrinogenemia, two hotspot mutations, FGA Arg35 and FGG Arg301 were identified in 60 % of patients and the remaining (40 %) had p.Arg38Thr mutation. The p.Val145Asp and two hotspot mutations, p.Arg35His, p.Arg35Cys, were identified for the first time in Iran. The overall median (range) bleeding score (BS) was 4 (0-6) in all patients and it was 3.5 (0-5) in dysfibrinogenemia. Cutaneous bleeding and menorrhagia were the most common bleeding manifestations.

CONCLUSION

There was a weak genotype-phenotype correlation in CFDs and patients with dysfibrinogenemia were more symptomatic than in previous studies. Despite ethnic's differences, the prevalence of hotspot mutations in dysfibrinogenemia was similar to the other studies.

Pediatric Fibrinogen PART II-Overview of Indications for Fibrinogen Use in Critically Ill Children

Bleeding is frequently seen in critically ill children and is associated with increased morbidity and mortality. Fibrinogen is an essential coagulation factor for hemostasis and hypofibrinogenemia is an important risk factor for bleeding in pediatric and adult settings. Cryoprecipitate and fibrinogen concentrate are often given to critically ill children to prevent bleeding and improve fibrinogen levels, especially in the setting of surgery, trauma, leukemia, disseminated intravascular coagulopathy, and liver failure. The theoretical benefit of fibrinogen supplementation to treat hypofibrinogenemia appears obvious, yet the evidence to support fibrinogen supplementation in children is sparce and clinical indications are poorly defined. In addition, it is unknown what the optimal fibrinogen replacement product is in children and neonates or what the targets of treatment should be. As a result, there is considerable variability in practice. In this article we will review the current pediatric and applicable adult literature with regard to the use of fibrinogen replacement in different pediatric critical care contexts. We will discuss the clinical indications for fibrinogen supplementation in critically ill children and the evidence to support their use. We summarize by highlighting current knowledge gaps and areas for future research.

Heterogeneity of congenital afibrinogenemia, from epidemiology to clinical consequences and management

Fibrinogen is a complex protein playing a major role in coagulation. Congenital afibrinogenemia, characterized by the complete absence of fibrinogen, is associated with major hemostatic defects. Even though the clinical course is unpredictable and can be completely different among patients, severe bleeding is the prominent symptom. Patients are also at increased risk of thrombosis and sometimes suffer from spontaneous spleen rupture, bone cysts and defective wound healing. Due to the relative rarity of afibrinogenemia, there are no evidence-based strategies for helping physicians in care of these patients. Fibrinogen supplementation is the keystone to prevent or treat bleeding events. In addition, fibrinogen, a pleiotropic protein with numerous physiological roles in immunity, angiogenesis and tissue repair, is involved in many diseases. Indeed, depletion of fibrinogen in animal models of infections, tumors and neurological diseases has an effect on the clinical course. The consequences for patients with afibrinogenemia still need to be investigated.

A Novel Nonsense Mutation in FGB (c.1421G>A; p.Trp474Ter) in the Beta Chain of Fibrinogen Causing Hypofibrinogenemia with Bleeding Phenotype

Congenital hypofibrinogenemia is a rare bleeding disorder characterized by a proportional decrease of functional and antigenic fibrinogen levels. Hypofibrinogenemia can be considered the phenotypic expression of heterozygous loss of function mutations occurring within one of the three fibrinogen genes (FGA, FGB, and FGG). Clinical manifestations are highly variable; most patients are usually asymptomatic, but may appear with mild to severe bleeding or thrombotic complications. We have sequenced all exons of the FGA, FGB, and FGG genes using the DNA isolated from the peripheral blood in two unrelated probands with mild hypofibrinogenemia. Coagulation screening, global hemostasis, and functional analysis tests were performed. Molecular modeling was used to predict the defect of synthesis and structural changes of the identified mutation. DNA sequencing revealed a novel heterozygous variant c.1421G>A in exon 8 of the FGB gene encoding a Bβ chain (p.Trp474Ter) in both patients. Clinical data from patients showed bleeding episodes. Protein modelling confirmed changes in the secondary structure of the molecule, with the loss of three β sheet arrangements. As expected by the low fibrinogen levels, turbidity analyses showed a reduced fibrin polymerisation and imaging difference in thickness fibrin fibers. We have to emphasize that our patients have a quantitative fibrinogen disorder; therefore, the reduced function is due to the reduced concentration of fibrinogen, since the Bβ chains carrying the mutation predicted to be retained inside the cell. The study of fibrinogen molecules using protein modelling may help us to understand causality and effect of novel genetic mutations.

A Novel Amino Acid Substitution, Fibrinogen Bβp.Pro234Leu, Associated with Hypofibrinogenemia Causing Impairment of Fibrinogen Assembly and Secretion

We identified a novel heterozygous variant, Bβp.Pro234Leu (fibrinogen Tokorozawa), which was suspected to be associated with hypofibrinogenemia. Therefore, we analyzed the assembly and secretion of this fibrinogen using Chinese hamster ovary (CHO) cells. To determine the impact on the synthesis and secretion of fibrinogen of the Bβp.P234L and γp.G242E substitutions, we established recombinant variant fibrinogen-producing CHO cell lines. Synthesis and secretion analyses were performed using an enzyme-linked immunosorbent assay (ELISA) and immunoblotting analysis with the established cell lines. In addition, we performed fibrin polymerization using purified plasma fibrinogen and in-silico analysis. Both Bβp.P234L and γp.G242E impaired the secretion and synthesis of fibrinogen. Moreover, immunoblotting analysis elucidated the mobility migration of the Bβγ complex in Bβp.P234L. On the other hand, the fibrin polymerization of fibrinogen Tokorozawa was similar to that of normal fibrinogen. In-silico analysis revealed that the Bβp.P234 residue is located in the contact region between the Bβ and γ chains and contacts γp.G242 residue. The present study demonstrated that the Bβp.P234L substitution resulted in hypofibrinogenemia by decreasing the assembly and secretion of fibrinogen. Therefore, there is a possibility that substitutions in the contact region between the Bβ and γ chains impact the assembly and secretion of fibrinogen.

Going beyond the mean in examining relationships of adolescent non-cognitive skills with health-related quality of life and biomarkers in later-life

Several studies have established associations between early-life non-cognitive skills and later-life health and health behaviours. However, no study addresses the more important policy concern about how this relationship varies along the health distribution. We use unconditional quantile regression to analyse the effects of adolescent non-cognitive skills across the distributions of the health-related quality of life at age 50 and biomarkers at age 45 years. We examine the effects of measures of conscientiousness, agreeableness and neuroticism recorded at age 16 for 3585 individuals from the National Child Development Study. Adolescent conscientiousness is positively associated with ability to cope with stress and negatively associated with risk of cardiovascular disease in middle-age. Adolescent agreeableness is associated with higher health-related quality of life and lower physiological 'wear and tear', but negatively associated with ability to cope with stress in middle-age. Adolescent neuroticism is associated with lower health-related quality of life, higher physiological 'wear and tear', and a higher risk of cardiovascular disease in middle-age. All of these associations are stronger at the lower end of the health distribution except for the cardiovascular risk biomarkers. These associations are robust to correcting for attrition using inverse probability weighting and consistent with causal bounds assuming proportional selection on observables and unobservables. They suggest policies that improve non-cognitive skills in adolescence could offer most long-term health benefit to those with the poorest health.

From Routine to Research Laboratory: Strategies for the Diagnosis of Congenital Fibrinogen Disorders

Congenital fibrinogen disorders (CFDs) encompass a heterogeneous group of fibrinogen defects with a wide spectrum of biological and clinical features. An accurate diagnosis is thus essential to assure the optimal management for the patient. Diagnosis involves a multistep approach starting with routine coagulation assays and assessment of functional and antigenic fibrinogen followed by identification of the molecular anomaly. However, the diagnosis of CFD can be challenging as the sensitivity and specificity of coagulation assays depend on the fibrinogen level as well as on the fibrinogen variant. In addition, patients suffering from CFD have a heterogeneous clinical course which is often unpredictable by routine coagulation assays. To better determine the patient's clinical phenotype, global hemostasis assays and an assessment of the fibrin clot properties are performed in research laboratories. In this review, we summarize the fibrinogen work-up highlighting some common pitfalls and provide an update of the research on CFD.

Genetic Variants in the FGB and FGG Genes Mapping in the Beta and Gamma Nodules of the Fibrinogen Molecule in Congenital Quantitative Fibrinogen Disorders Associated with a Thrombotic Phenotype

Fibrinogen is a hexameric plasmatic glycoprotein composed of pairs of three chains (Aα, Bβ, and γ), which play an essential role in hemostasis. Conversion of fibrinogen to insoluble polymer fibrin gives structural stability, strength, and adhesive surfaces for growing blood clots. Equally important, the exposure of its non-substrate thrombin-binding sites after fibrin clot formation promotes antithrombotic properties. Fibrinogen and fibrin have a major role in multiple biological processes in addition to hemostasis and thrombosis, i.e., fibrinolysis (during which the fibrin clot is broken down), matrix physiology (by interacting with factor XIII, plasminogen, vitronectin, and fibronectin), wound healing, inflammation, infection, cell interaction, angiogenesis, tumour growth, and metastasis. Congenital fibrinogen deficiencies are rare bleeding disorders, characterized by extensive genetic heterogeneity in all the three genes: FGA, FGB, and FGG (enconding the Aα, Bβ, and γ chain, respectively). Depending on the type and site of mutations, congenital defects of fibrinogen can result in variable clinical manifestations, which range from asymptomatic conditions to the life-threatening bleeds or even thromboembolic events. In this manuscript, we will briefly review the main pathogenic mechanisms and risk factors leading to thrombosis, and we will specifically focus on molecular mechanisms associated with mutations in the C-terminal end of the beta and gamma chains, which are often responsible for cases of congenital afibrinogenemia and hypofibrinogenemia associated with thrombotic manifestations.

Congenital afibrinogenemia in a patient with vascular abnormalities and a novel variant: clinical-molecular description and literature review

: The objective is to report a patient with congenital afibrinogenemia and vascular abnormalities and also review the clinical and molecular issues. The female proband, diagnosed with congenital afibrinogenemia, was admitted at a hospital due to a hemorrhagic shock. Angiotomography revealed ectasias from ascending branch to the abdominal aorta, with multiple calcifications and atheroma. Clinical exome identified a homozygous novel pathogenic variant in FGG gene. In our review the main symptom, at diagnosis, was umbilical cord bleeding and the degree of clinical involvement varied from asymptomatic to severe. The FGA gene was the most affected and possible hot spots were observed. Variants considered as loss of function were the most frequent. The association of vascular abnormalities in a patient with congenital afibrinogenemia alerts for a closer follow-up of vascular issues in these patients.

Women With Congenital Hypofibrinogenemia/Afibrinogenemia: From Birth to Death

Congenital fibrinogen disorders are a group of most frequent rare coagulation disorder, characterized by deficiency and/or defects in the fibrinogen molecule. Quantitative disorders include hypofibrinogenemia and afibrinogenemia. Due to their specific physiological characteristics, female patients tend to have congenital hypofibrinogenemia/afibrinogenemia, such as spontaneous recurrent abortion, menorrhagia, infertility, antepartum and postpartum hemorrhage, and so on. Current studies of congenital hypofibrinogenemia/afibrinogenemia mainly focus on different types of fibrinogen mutations, etiology/pathogenesis, and some rare case reports of the diseases. So far, there is no study available to systematically review the specific features of female patients with congenital bleeding disorders. This review aims to deal with hematological, gynecologic and obstetric issues, and relevant clinical management of congenital hypofibrinogenemia/afibrinogenemia at different life stages of female patients. We believe this review provides valuable reference for clinicians in the field of hematology, obstetrics, as well as gynecology.

Observational Safety Study of Clottafact® Fibrinogen Concentrate: Real-World Data in Mexico

BACKGROUND AND OBJECTIVE

The use of fibrinogen concentrate to treat or prevent major bleeding with regard to potential adverse reactions has not been free of controversy. Our objective was to perform a post-authorization safety study to describe the use of Clottafact^® (LFB Biomedicaments) fibrinogen concentrate in real-life medical practice in Mexico.

METHODS

This was a prospective, observational study that collected and evaluated information between January 2017 and June 2019 related to suspected serious adverse reactions (SUSARs) during and after Clottafact^® infusion.

RESULTS

Information from 40 subjects was analyzed; 43% were women (n = 17), mean age was 39.05 ± 26.8 years (range 0-91 years). The medical specialties included in this analysis were cardiac surgery - 52.5% of the cases, gynecology/obstetrics - 17.5%, general surgery and orthopedics - 12.5% each, and hematology and neurosurgery - 2.5%, respectively. Mean plasma fibrinogen levels before and after Clottafact^® infusion were 2.58 g/L and 4.02 g/L; p = 0.001, respectively. The mean Clottafact^® dose was 2.20 ± 0.77 g. One patient presented SUSARs (dry mouth and dysgeusia) with drug administration, which ceased after treatment discontinuation.

CONCLUSIONS

In this real-life post-marketing study, the safety profile of Clottafact^® was very similar to previous reports. Thus, Clottafact^® shows a favorable safety profile in clinical practice.

Atypical antipsychotic clozapine binds fibrinogen and affects fibrin formation

Clozapine is an atypical antipsychotic used for the treatment of schizophrenia. The prescribed target daily doses may reach 900 mg. Literature studies report a connection between clozapine usage and thrombosis development. Our in vitro study aimed to provide insight into molecular bases of this observation, investigating clozapine binding to fibrinogen, the main plasma protein involved in hemostasis. Fibrinogen/clozapine interaction was confirmed by protein fluorescence quenching, with an affinity constant of 1.7 × 10⁵ M^-1. Direct interactions did not affect the structure of fibrinogen, nor fibrinogen melting temperature. Clozapine binding affected fibrin formation by reducing coagulation speed and thickness of fibrin fibers suggesting that in the presence of clozapine, fibrinogen may acquire thrombogenic characteristics. Although no difference in fibrin gel porosity was detected, other factors present in the blood may act synergistically with altered fibrin formation to modify fibrin clot, thus increasing the risk for development of thrombosis in patients on clozapine treatment. ORAC and HORAC assays showed that clozapine reduced free radical-induced oxidation of fibrinogen. All observed effects of clozapine on fibrinogen are dose-dependent, with the effect on fibrin formation being more pronounced.