A novel mutation in the FGG gene causes hypofibrinogenemia in a Chinese family

Congenital fibrinogen disorders are a group of coagulation deficiencies caused by fibrinogen defects and are divided into four types, including afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia. In this study, we collected a family with hypofibrinogenemia, and genetics analysis identify a novel pathogenic variants (c.668G > C, p.Arg223Thr) in the FGG gene. And electron microscope observation revealed significant changes in the ultrastructure of fibrin of the proband. Our research expands the phenotypic and genetic spectrum associated with the FGG gene, which would facilitate in genetic counselling and prenatal genetic diagnosis.

Medfødte fibrinogensygdomme

Congenital fibrinogen disorders are rare pathologies of the haemostasis, comprising afibrinogenaemia, hypofibrinogenaemia, dysfibrinogenaemia and hypodysfibrinogenaemia. Phenotypic manifestations are variable, patients may be asymptomatic or suffer from bleeding or thrombosis. Most of congenital fibrinogen disorders are coincidentally discovered. Fibrinogen concentrate is used to treat bleeding, whereas low-molecular weight heparin is most often administered for the treatment of thrombotic complications. The aim of this review is to provide an update of the knowledge of congenital fibrinogen disorders for Danish physicians.

[Genetic analysis of a Chinese pedigree affected with Congenital dysfibrinogenemia due to variant of FGG gene]

OBJECTIVE

To explore the coagulation deficit and genetic basis for a Chinese pedigree affected with Congenital dysfibrinogenemia (CD).

METHODS

Peripheral venous blood samples of the proband and her family members (including 4 individuals from three generations) were subjected to routine blood test and assays of liver and kidney functions and viral hepatitis to exclude related diseases. Clauss method and DFg-PT method were used to determine the fibrinogen activity (Fg:C), and an immunoturbidimetric assay was used to determine the level of fibrinogen antigen (Fg:Ag). All of the exons (22 in total) and their flanking sequences of the FGA, FGB and FGG genes were amplified by PCR and directly sequenced. Variants in the coding regions of the three genes and transcriptional splicing sites were screened by using Mutation SurveyorTM software.

RESULTS

The Clauss method showed that Fg:C was significantly reduced in the proband and her father, whilst her mother and son were normal. With the DFg-PT method, the proband, her parents and son were all within the normal range. The Fg:C/Fg:Ag ratio of the proband and her father was lower than 0.7, whilst her mother and son were above 0.7. No significant change in the prothrombin time, activated partial thromboplastin clotting time and thrombin time was noted. Two genetic variants were detected, which included a homozygous missense variant in the FGA gene [c.991A>G (p.Thr331Ala)], which was predicted to be benign, and a heterozygous missense variant of the γ chain of the FGG gene [c.1211C>G (p.Ser404Phe)], which is located in a conserved region and unreported in the CLINVAR/HGMD/EXAC/1000G databases and literature.

CONCLUSION

This pedigree has conformed to the autosomal dominant inheritance of CD. The c.1211C>T (p.Ser404Phe) missense variant of the γ chain of the FGG gene probably underlay the pathogenesis of CD in this pedigree. The variant was unreported previously and named as "Fibrinogen Harbin II Ser404Phe".

Congenital Hypofibrinogenemia; An Unexpected Culprit Of Blindness In An Infant

Congenital hypofibrinogenemia is a rare haematological disorder in which the production of functional fibrinogen is impaired because of the inherited mutation. Hypofibrinogenemia affects the coagulation cascade leading to bleeding diathesis and one of its manifestations can be recurrent Vitreous haemorrhages, sometimes leading to irreversible loss of vision. Therefore, Hypofibrinogenemia must be included in the differential diagnosis of Vitreous haemorrhage, particularly in young children. We report a case of a four months old female infant who was brought by her mother to the unit since she was afraid that the child might be unable to see since she was not following things for the last one month. Her ophthalmologic examination revealed bilateral vitreous haemorrhages. Further workup for the cause of the bleeding confirmed the diagnosis of hypofibrinogenemia which was then managed accordingly.

[Analysis of a pedigree affected with congenital dysfibrinogenemia due to a novel Gly31Glu mutation of FGA gene]

OBJECTIVE

To analyze the phenotype and genotype of a pedigree affected with congenital dysfibrinogenemia.

METHODS

Liver and kidney functions of the proband and her relatives were determined. Coagulation tests including prothrombin time (PT), activated partial thromboplastin time (APTT) and thrombin time(TT), fibrin(ogen) degradation products (FDPs), D-dimer(D-D) and the calibration experiment of protamine sulfate of against plasma TT were detected in the proband and her predigree members. The activity and antigen of fibrinogen (Fg) in plasma were measured by Clauss method and immunonephelometry method, respectively. All of the exons and exons-intron boundaries of the three fibrinogen genes (FGA, FGB and FGG) were subjected to PCR amplification and Sanger sequencing. Potential influence of the suspected mutations were analyzed with bioinformatics software including PolyPhen-2, SIFT and Mutation Taster.

RESULTS

The proband had normal PT, APTT, FDPs, D-D and prolonged TT (31.8 s). The activity of fibrinogen (Fg) in plasma was significantly decreased but the antigen was normal. Genetic analysis revealed a heterozygous c.92G>A (p.Gly31Glu) mutation in exon 2 of the FGA gene. Family studies revealed that the mother carried the same mutation. Bioinformatic analysis suggested that the mutation may affect the function of Fg Protein.

CONCLUSION

The dysfibrinogenemia was probably caused by the novel Gly31Glu mutation of the FGA gene.

Clinical pharmacology, efficacy and safety study of a triple-secured fibrinogen concentrate in adults and adolescent patients with congenital fibrinogen deficiency

Essentials A novel fibrinogen concentrate was evaluated in patients with congenital fibrinogen deficiency. An open-label, phase 2-3 trial studied pharmacology, efficacy, and safety in patients >6 years. The product offers safe and effective therapy in the treatment and prophylaxis of bleeding. Data in recovery show the need of adjusted treatment and further investigation in children. SUMMARY: Background Single-factor replacement therapy is considered the most suitable treatment option for hereditary fibrinogen deficiency. A triple-secured plasma-derived human fibrinogen product was developed to increase the safety of the former fibrinogen concentrate. Objectives This non-randomized, open-label, prospective study investigated pharmacokinetics, efficacy, and safety of a novel fibrinogen concentrate (FibCLOT® /CLOTTAFACT® LFB, France) in inherited deficiency. Patients/Methods Fourteen patients ≥40 kg received fibrinogen concentrate for pharmacology and 16 ≥ 23 kg received treatment for bleeding or surgery. Each treatment was followed by a 3-week safety observation period. Key outcomes included number of infusions, dose, bleeding control, daily assessment, hemoglobin, blood loss, transfusions, and physicians' global assessment of response. Results Incremental recovery was 2.35 mg mL-1  per mg kg-1 and maximal concentration 1.41 g L-1 (geometric mean) after 0.060 g kg-1 infusion in 14 afibrinogenemic patients. Terminal half-life was 69.3 h (non-compartmental analysis). The maximum clot firmness was increased by a mean of 10.3 mm from baseline to maximal effect. Sixteen patients participated to the efficacy phase: 32 bleeding episodes were treated in 9 patients, and 15 patients underwent 38 surgical/invasive procedures. All patients achieved appropriate hemostasis: response to treatment was successful in all bleeds (95% CI, 0.89-1.00) and procedures (95% CI, 0.91-1.00). Most (94%) bleeds were controlled with a single infusion (median 0.050 g kg-1 ). Two patients experienced asymptomatic distal venous thromboses identified by systematic ultrasound. Conclusion FibCLOT® /CLOTTAFACT® showed a pharmacokinetic profile comparable to that of other fibrinogen concentrates and provides safe and clinically effective substitution therapy for fibrinogen-deficient patients.

Congenital afibrinogenemia: a case report of a spontaneous hepatic hematoma

INTRODUCTION

Afibrinogenemia is a rare coagulation disorder. Clinical features of spontaneous bleeding, bleeding after minor trauma, or after surgery have been described as well as thrombo-embolic complications. In this article, we presented the case of a 19-year old female with congenital afibrinogenemia who was admitted with a spontaneous intrahepatic hematoma.

CONCLUSIONS

Supportive treatment including transfusion and fibrinogen administration, associated with repeated packing surgeries and selective embolization, were successfully performed.

Afibrinogénémie congénitale: à propos d’une observation

L’afibrinogénémie est une dyscrasie rare caractérisée par un déficit constitutionnel en fibrinogène. Elle se transmet sur un mode autosomique récessif. Les manifestations hémorragiques sont variables et peuvent mettre en jeu le pronostic vital. Un peu plus de 250 cas ont été publiés à nos jours. Nous rapportons un nouveau cas d’afibrinogénémie congénitale chez une enfant de 3 ans et demi hospitalisée pour hématémèse de moyenne abondance. A travers ce cas, nous rappelons les différents aspects de cette affection sur les plans clinique, biologique, génétique ainsi que thérapeutique.

In vitro rescue of FGA deletion by lentiviral transduction of an afibrinogenemic patient's hepatocytes

BACKGROUND

Congenital afibrinogenemia is a rare inherited autosomal recessive disorder in which a mutation in one of three genes coding for the fibrinogen polypeptide chains Aα, Bβ and γ results in the absence of a functional coagulation protein. A patient with congenital afibrinogenemia, resulting from an FGA homozygous gene deletion, underwent an orthotopic liver transplant that resulted in complete restoration of normal hemostasis. The patient's explanted liver provided a unique opportunity to further investigate a potential novel treatment modality.

OBJECTIVE

To explore a targeted gene therapy approach for patients with congenital afibrinogenemia.

METHODS AND RESULTS

At the time of transplant, the patient's FGA-deficient hepatocytes were isolated and transduced with lentiviral vectors encoding the human fibrinogen Aα-chain. FGA-transduced hepatocytes produced fully functional fibrinogen in vitro.

CONCLUSIONS

Orthotopic liver transplantation is a possible rescue treatment for failure of on-demand fibrinogen replacement therapy. In addition, we provide evidence that hepatocytes homozygous for a large FGA deletion can be genetically modified to restore Aα-chain protein expression and secrete a functional fibrinogen hexamer.

Intraosseous pseudotumor in a child with hypofibrinogenemia

Intraosseous pseudotumor (i.e. chronic, encapsulated, hemorrhagic fluid collection that can be seen in any portion of the tubular bones) is an uncommon complication of severe hemophilia; however, it can occur with other rare bleeding disorders. We present the case of an 11-year-old girl with hypofibrinogenemia who had multiple intramedullary lesions that were consistent with intramedullary pseudotumor associated with this rare bleeding disorder. Percutaneous biopsy of a pseudotumor is contraindicated due to the high prevalence of complications, including life-threatening bleeding. Therefore, radiologists should make the diagnosis with characteristic MR imaging findings in a patient with a severe coagulation disorder.

FGB mutations leading to congenital quantitative fibrinogen deficiencies: an update and report of four novel mutations

INTRODUCTION

Causative mutations leading to congenital quantitative fibrinogen are frequently clustered in FGA encoding the fibrinogen Aα-chain. Mutations of FGB encoding the Bβ-chain are less common and of interest since the Bβ-chain is considered the rate-limiting factor in the hepatic production of the fibrinogen hexamer.

METHOD

Four novel FGB mutations were identified in two afibrinogenemic (one new-born and one 30 years old male) and hypofibrinogenemic (a 49 years old female) patient, with heterogeneous thrombotic and bleeding phenotype. The human fibrinogen beta chain precursor protein sequence (P02675) was obtained from the UniProt database. The resulting models were analysed in SwissPdbViewer 4.1 and POV-Ray 3.7.

RESULTS

The FGB c.895T>C p.Y299H (numbering from the initiator Met) and the FGB c.1415G>T p.G472V were predicted to be deleterious by SIFT analysis. The first replaces an uncharged aromatic amino acid side chain by a positively charged side chain modifying the balance in the distribution of hydrophobic and hydrophilic of the 10 Å neighbourhood residues. The second replaces one non-charged aliphatic side chain by another without any changes for the 10 Å surrounding region. The FGB c.352C>T p.Q118X leads to a severe premature termination codon and the FGB intron 4: IVS4-1G>C (c719-1G>C) leads to skipping of exon 5 or usage of a cryptic acceptor site located upstream or downstream of the normal site.

CONCLUSIONS

The continuous characterization of novel molecular defects responsible for fibrinogen deficiency combined with modelling of mutant proteins will continue to provide a better comprehension of the complexity of fibrinogen synthesis and physiology.

Role of fibrinogen in massive injury

Coagulation is a complex cascade whose intact functioning is essential in helping control hemorrhage after injury. While traditionally ascribed to the combined effects of acidosis, hypothermia, factor consumption and factor dilution, coagulopathy is also directly related to injury as well as hypofibrinogenemia and hyperfibrinolysis. Low fibrinogen concentration is readily determined with standard laboratory profiling, but direct analysis of hyperfibrinolysis relies on either thromboelastography or rotational thromboelastometry. Both conditions offer opportunities for therapeutic intervention, and inhibition or abrogation of hyperfibrinolysis in particular may significantly improve survival in patients with injury and massive hemorrhage. Herein, we explore the underpinnings of trauma associated coagulopathy, the basic science behind the role of fibrinogen in acute traumatic coagulopathy, and the rationale behind and the data derived from management of hypofibrinogenemia as well as hyperfibrinolysis.

Fibrinogen

Fibrinogen is the final essential building block of the clotting process. Thus, all of the preliminary "cause and effect" events in the clotting cascade rely on the work of this molecule to measure their success. The most commonly used laboratory method for measuring fibrinogen is the Clauss fibrinogen assay. The Clauss fibrinogen assay is a quantitative, clot-based, functional assay. The assay measures the ability of fibrinogen to form fibrin clot after being exposed to a high concentration of purified thrombin. Plasma samples are pre-diluted which minimize assay interference from substances like heparin and fibrinogen degradation products. In brief, the diluted plasma is incubated at 37°C prior to the addition of the pre-warmed (37°C) thrombin reagent. From the exact moment of the addition of thrombin, the time to clot is measured. The clotting time in seconds is interpolated from a standard curve made using various dilutions of assayed standard plasma. The following chapter includes detailed information on the Clauss fibrinogen assay. Other fibrinogen assays used include fibrinogen levels derived from prothrombin time assays and antigenic methods. Fibrinogen measurements using the prothrombin time and antigenic based assays are described in brief.

[Anesthetic management of a parturient with congenital afibrinogenemia undergoing cesarean section]

A 29-year-old parturient with congenital afibrinogenemia was scheduled to receive cesarean section 38 weeks 2 days of gestation. Due to the bleeding ter dency by her abnormality of fibrinogen and afibrinogenemia, general anesthesia was chosen. In addition to routine administration of fibrinogen, perioperative supplementation of fibrinogen with the meticulous evaluation of the coagulation and fibrinolysis status using rotation thromboelastometry (ROTEM) enabled the patient to deliver a healthy baby without any hematological complications. The ROTEM was a useful device to check coagulopathy and fibrinolysis in this patient.

[Comparison of fibrinogen synthesis and secretion between novel variant fibrinogen, nagakute (gamma305Thr --> Ala), and other variants located in gamma305-308 residues]

We found and identified a novel heterozygous dysfibrinogenemia with gammaT305A (ACA --> GCA) mutation in a 6-month old boy. Since his plasma antigenic concentration of fibrinogen was 1.12g/l and less than the lower limit of the reference interval, we guessed that the production of a variant fibrinogen might be a partial defect. To clarify this speculation, we altered the gamma-chain expression vector, transfected it into Chinese Hamster Ovary(CHO) cells, and synthesized recombinant gammaT305A fibrinogen alongside three other variant fibrinogens, gammaS306P, gammaH307Y, and gammaN308K, and the wild type (gammaN) fibrinogen. Fibrinogen concentration ratio of culture media/cell lysates decreased in the order of gammaT305A-, gammaS306P-, gammaH307Y-CHO cells, all three being lower in comparison to the gammaN-CHO cells. Western blotting analyses indicated that all of variant gamma-chains were assembled into fibrinogen molecules in the cells. These data indicate the possibility that secretion of gamma T305A-fibrinogen is slightly impaired and variant fibrinogen is accumulated in the cell. Of interest, the secretion of gammaH307Y-fibrinogen was decreased the most, whereas that of the gammaN308K-CHO cells was not affected. The tertiary structure of the yC nodule indicated that gamma305T-gamma307H residues are located in the inside of the nodule. In contrast, that of gamma308N is located on surface of the nodule. In conclusion, our results showed the variant fibrinogen, gammaT305A, has characteristics not only of dysfibrinogenemia, but also might be hypofibrinogenemia, namely, hypo/dysfibrinogenemia. Furthermore, gamma306S-gamma307H residues of the gammaC nodule play crucial roles for protein synthesis and fibrin polymerization.

Diagnosis and non-surgical periodontal management in congenital afibrinogenemia: report of a rare case

Medical records have an important role in the diagnosis and planning treatment modalities of periodontal diseases. Surgical periodontal procedures can pose severe complications if the underlying systemic condition is not recorded. To substantiate this, we present a rare case of afibrinogenemia that was reported to the Department of Periodontics, Narayana Dental College, Nellore, India. The present case report gives details of fibrinogen disorder and the dental management of such cases.

Fibrinogen replacement therapy for congenital fibrinogen deficiency

This review of published studies was conducted to derive data on patients with congenital fibrinogen deficiency (CFD), including dosing of fibrinogen replacement therapy, outcome, and adverse events, either temporally related or distant to fibrinogen replacement, in order to assist clinicians in developing treatment plans for patients with CFD. A systematic review was performed of case reports identified by a MEDLINE search between 1961 and 2010. Eligible studies included subjects with a diagnosis of CFD who received fibrinogen replacement. An attempt was made to extract dose, frequency, duration, hemostatic efficacy and adverse events such as thrombosis or allergic reactions. Reported thrombotic events distant from fibrinogen replacement were also recorded. From 104 papers reviewed, a total of 50 cases were identified: afibrinogenemia (35), hypofibrinogenemia (6), and dysfibrinogenemia (9). Fibrinogen replacement therapy was generally effective in preventing or treating bleeding in doses adequate to achieve and maintain fibrinogen activity above 50-100 mg dL(-1) (non-surgical and obstetric use) or 100-200 mg dL(-1) (surgical prophylaxis). Increased fibrinogen clearance was observed with massive hemorrhage, major surgery, and advanced pregnancy. Obstetric outcomes were optimized when fibrinogen replacement was initiated prior to conception. Uncontrolled hemorrhage, allergic reactions and antibody formation were rare events. However, thromboses, both related and unrelated to fibrinogen replacement, occurred in 15 of 50 (30%) patients overall, and in eight of 12 (67%) adult non-obstetric patients with afibrinogenemia. Published fibrinogen replacement regimens are presented for 50 CFD patients. Fibrinogen replacement therapy requires careful monitoring of fibrinogen levels. Afibrinogenemia is associated with thromboembolic complications with or without treatment.

Congenital afibrinogenemia in 10 offspring of uncle-niece marriages

Two unrelated large sibships, including 10 cases of congenital afibrinogenemia among 27 sibs, are reported. Both sibships were the product of uncle-niece marriages. They were not selected for any particular clinical manifestation and should provide some information on genetic fitness. Six of the patients died in childhood, two affected boys are adolescent and two affected patients are young women. Two of the four survivors had spontaneous ruptures of the spleen. Fitness in this very rare disease seems to be close to zero and the inheritance is autosomal recessive.

Pseudo-exon activation caused by a deep-intronic mutation in the fibrinogen ?-chain gene as a novel mechanism for congenital afibrinogenaemia

Congenital afibrinogenaemia, characterized by severe fibrinogen deficiency, is caused by mutations within FGA, FGB or FGG. Conventional sequencing of coding regions and splice signals of these three genes did not reveal any mutation in an afibrinogenaemic proband. After confirming disease co-segregation with the fibrinogen cluster, full intron sequencing was tackled leading to the identification of a novel transvertion within FGG intron 6 (IVS6-320A-->T). Its effect on mRNA processing was evaluated in-vitro: the in-frame inclusion of a 75-bp pseudo-exon carrying a premature stop was found, representing the first report of pseudo-exon activation as a mechanism leading to afibrinogenaemia.

Retrochorionic hematoma in congenital afibrinogenemia: resolution with fibrinogen concentrate infusions

Without treatment, pregnancies in patients with congenital afibrinogenemia terminate in miscarriage at 5-6 weeks of gestation. Animal model studies have suggested that implantation site bleeding contributes to miscarriage in afibrinogenemia; however, retrochorionic hematoma in human congenital afibrinogenemia has not been previously observed. A patient with congenital afibrinogenemia receiving fibrinogen prophylaxis developed a retrochorionic hematoma in the first trimester. With continuous intensified fibrinogen concentrate replacement the hematoma resolved over 6 weeks, and the patient delivered a healthy infant. Median fibrinogen levels in the first trimester were 48 mg/dL and in second and third trimester 44 mg/dL. Median fibrinogen levels under 60 mg/dL may be adequate to maintain pregnancy in patients with congenital afibrinogenemia, although it is possible that higher levels might reduce the risk of hemorrhagic events.

Identification of three FGA mutations in two Chinese families with congenital afibrinogenaemia

Congenital afibrinogenaemia is a rare autosomal recessive disorder, characterized by the complete absence or extremely reduced level of fibrinogen (Fg). We attempted to analyse the phenotype and genotype in two Chinese families with congenital afibrinogenaemia. Coagulation studies including activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) and Fg were performed in the patients and other family members. All the exons, exon-intron boundaries and promoter regions of three Fg genes (FGA, FGB and FGG) were screened by direct sequencing. Three patients in two families suffered from moderate to severe haemorrhage. Their APTT, PT and TT were extremely prolonged and plasma Fg levels were undetectable by Clauss method and extremely reduced by immunoassay. Genetic analysis revealed three FGA mutations in three patients including one novel mutation. In family 1, patient 1 was detected compound heterozygous mutations in FGA, g.1892-1899delAGTA/GTAA from her patriline and g.1978-g.3215del1238 bp from her matriline. In family 2, a homozygous Gln203X in Aalpha-chain was found in both patients 2 and 3 due to consanguineous marriage. All these mutations were null mutations, which could produce premature stop codons in FGA. It can be indicated that with more genetic analysis performed on afibrinogenaemia patients all over the world, there is no distinct difference in geographical distribution of Fg gene mutations. Gln203X in Aalpha-chain was first reported in this study, which may help to further understand the function of Aalpha-chain.

Molecular basis of fibrinogen deficiency

Inherited fibrinogen disorders can be classified into qualitative and quantitative anomalies: dysfibrinogenemia is characterised by normal circulating levels of fibrinogen with abnormal function; hypofibrinogenemia and afibrinogenemia are characterised by reduced or absent fibrinogen in circulation respectively,while hypodysfibrinogenemia is defined by reduced fibrinogen with reduced function. All are due to mutations in one of the three fibrinogen genes, FGA, FGB and FGG, which are clustered in a region of 50 kb on the long arm of human chromosome 4. The aim of this review is to illustrate the diverse molecular mechanisms by which mutations lead to fibrinogen deficiency, in particular in congenital afibrinogenemia.

[Afibrinogenemia: description of a case with recurrent intracranial bleeding]

INTRODUCTION

Congenital afibrinogenemia is a very rare autosomal recessive disorder of the coagulation. The lack of fibrinogen makes the blood inclotting and patients suffer from bleeding at a minimal trauma. It is usually noticed within the first few days of life because of the umbilical cord bleeding. Intracerebral hematoma is infrequent.

CASE DESCRIPTION

46-year-old woman who suffers from congenital afibrinogenemia and has five episodes of intracerebral bleeding, all of them in the posterior circulation. As a complication, she also presents an epilepticus status and the therapy with concentrated fibrinogen caused pulmonary thromboembolism.

CONCLUSIONS

After analysing the cases described in literature, there are evidences that the majority of the intracerebral hematoma are located in the posterior circulation. A few patients developed major thomboemolisms following infusion with concentrated fibrinogen and there are only isolated descriptions of beneficial prophylactic effects. So, it is would necessary studies more extensive research to achieve effectiveness in the prevention of the bleeding.

Hemi-spinal cord infarction due to vertebral artery dissection in congenital afibrinogenemia

Isolated ischemia of the cervical spinal cord is an uncommon but increasingly recognized complication of vertebral artery dissection (VAD). The authors report a young patient with congenital afibrinogenemia, who developed VAD with extensive unilateral spinal cord infarction, probably caused by local compression of spinal radicular feeders at their origin by vertebral artery hematoma.

Quality control of fibrinogen secretion in the molecular pathogenesis of congenital afibrinogenemia

Congenital afibrinogenemia is a rare bleeding disorder characterized by the absence in circulation of fibrinogen, a hexamer composed of two sets of three polypeptides (Aalpha, Bbeta and gamma). Each polypeptide is encoded by a distinct gene, FGA, FGB and FGG, all three clustered in a region of 50 kb on 4q31. A subset of afibrinogenemia mutations has been shown to specifically impair fibrinogen secretion, but the underlying molecular mechanisms remained to be elucidated. Here, we show that truncation of the seven most C-terminal residues (R455-Q461) of the Bbeta chain specifically inhibits fibrinogen secretion. Expression of additional mutants and structural modelling suggests that neither the last six residues nor R455 is crucial per se for secretion, but prevent protein misfolding by protecting hydrophobic residues in the betaC core. Immunofluorescence and immuno-electron microscopy studies indicate that secretion-impaired mutants are retained in a pre-Golgi compartment. In addition, expression of Bbeta, gamma and angiopoietin-2 chimeric molecules demonstrated that the betaC domain prevents the secretion of single chains and complexes, whereas the gammaC domain allows their secretion. Our data provide new insight into the mechanisms accounting for the quality control of fibrinogen secretion and confirm that mutant fibrinogen retention is one of the pathological mechanisms responsible for congenital afibrinogenemia.

Digital skin necrosis in congenital afibrinogenaemia associated with hepatitis C virus infection, mixed cryoglobulinaemia and anticardiolipin antibodies

Congenital afibrinogenaemia is a rare genetic disorder transmitted as an autosomal recessive trait and characterized by the complete absence of fibrinogen in the plasma. We report a 41-year-old woman who suffered from congenital afibrinogenaemia and hepatitis C viral infection and presented with ischaemic necrosis and livedo of the toes. Laboratory investigations showed the presence of mixed cryoglobulinaemia and anticardiolipin antibodies. Resolution occurred with plasmapheresis. We discuss the pathophysiology of this unusual condition and review the literature for skin manifestations associated with this rare haemostasis disorder.

[Fibrinogen substitution. Use in the treatment of bleeding due to lack of fibrinogen]

Fibrinogen is critically important in haemostasis. The concentration of fibrinogen in plasma is usually between 2 and 4 g/l (6-13 micromol/l). No detectable fibrinogen is found in afibrinogenaemia, a condition characterised by dramatic bleeding, while dys- and hypofibrinogenaemia have a lower-than-normal activity of functional fibrinogen. Acquired fibrinogen deficiency may occur with a variety of underlying pathologies. Fibrinogen substitution may be done with fresh-frozen plasma, cryoprecipitate and virally inactivated concentrates of fibrinogen.

Efficacy and tolerability of a pasteurised human fibrinogen concentrate in patients with congenital fibrinogen deficiency

The efficacy and tolerability of a pasteurised human fibrinogen concentrate were assessed in an open, multi-centre, non-controlled retrospective study in patients with congenital fibrinogen deficiency. Haemostatic efficacy was assessed by laboratory investigation and clinical observation. The study included 12 patients (afibrinogenaemia, n = 8; hypofibrinogenaemia, n = 3; dysfibrinogenaemia combined with hypofibrinogenaemia, n = 1). Fibrinogen substitution was indicated: to stop an ongoing bleed; as prophylaxis before surgery; or for routine prophylaxis to prevent spontaneous bleeding. In total, 151 fibrinogen infusions were recorded. The median single dosage was 63.5mg/kg body weight for bleeding events or surgery and 76.9 mg/kg for prophylaxis. The median total dose per event for bleeding events or surgery was 105.6 mg/kg. Fibrinogen was administered in 26 bleeding episodes; 11 surgical operations; and 89 prophylactic infusions, of which 86 were received by one patient. The median response (n = 8) was 1.5 mg/dl per substituted mg of fibrinogen per kg body weight (0.8-2.3). The median in vivo recovery (n = 8) was 59.8% (32.5-93.9). Clinical efficacy was very good in all events with the exception of one surgical procedure, where it was moderate. No intercurrent bleeding occurred during prophylaxis. All but one infusion was well tolerated; the patient, who was administered 86 prophylactic infusions, experienced an anaphylactic reaction after the 56th infusion. In addition, one patient developed deep vein thrombosis and non-fatal pulmonary embolism with treatment for osteosynthesis after collum femoris fracture. Fibrinogen substitution could not be excluded as a contributing factor in this high-risk patient. Substitution with pasteurised human fibrinogen concentrate in patients with congenital fibrinogen deficiencies is efficient and generally well tolerated.

A novel nonsense mutation in the FGA gene in a Chinese family with congenital afibrinogenaemia

Congenital afibrinogenaemia is a rare autosomal recessive coagulation disorder. Here we describe the genetic defect in the fibrinogen A alpha-chain underlying afibrinogenaemia in a Chinese family. The proposita had a life-long bleeding tendency, both her parents and paternal grandparents had a consanguineous marriage. The blood-clotting indices of the proposita and her father were prolonged, and their functional and immunologic fibrinogen was absent. To identify the mutations of fibrinogen genes in this family, all the exons and exon-intron boundaries of the three fibrinogen genes (FGA, FGB, FGG) were amplified by polymerase chain reaction, and direct sequencing of polymerase chain reaction products was performed, then the restriction endonuclease (RsaI) analysis was used to confirm the mutation. A homozygous C --> T mutation was found at nucleotide 3108 in exon 4 of the FGA gene of the proposita and her father; it is a null mutation predicting to produce severely truncated A alpha-chains because of the presence of premature termination at the Gln 150 codon (or truncated at the 131 residues according to the mature A alpha-chain). Her mother and some other family members were heterozygous. The g.3108C --> T (Gln150 --> stop) nonsense mutation in the FGA gene is a novel genetic defect of congenital afibrinogenaemia that, to our knowledge, has not been described previously.

[Fibrinogen beta chain gene mutation contributes to one congenital afibrinogenemia]

OBJECTIVE

To identify the fibrinogen (Fg) gene mutations in a Chinese pedigree of congenital afibrinogenemia.

METHODS

The plasma Fg activity and protein of the proband and his family members were detected. Genomic DNA was isolated from the peripheral blood mononuclear cells. All the exons and exon-intron boundaries of fibrinogen gene were amplified by PCR and sequenced thereafter.

RESULTS

Two mutations, 7972 del G in FGB and T2543A in FGG, were found in the proband.

CONCLUSIONS

FGG2543 is a polymorphism site, which lead to the polymorphism of gamma144 I/K. The G deletion at base 7972 of FGB contributes to the frameshift mutation after amino acid 419, resulting in the truncated beta chain without the terminal 27 amino acids. The latter may contributes to the pathogenetic mechanisms in Chinese congenital afibrinogenemia patients. The G deletion at base 7972 of FGB is identified for the first time.

[Congenital afibrinogenemia associated with a novel nonsense mutation in the FGA gene]

OBJECTIVE

To identify the genetic defect underlying congenital afibrinogenemia in a Chinese family.

METHODS

Plasma fibrinogen (Fg) was assessed by both Clauss method and immunonephelometry. Genomic DNA was isolated from peripheral blood of the proband and 13 members of her family. All the exons and exon-intron boundaries of the three fibrinogen genes (FGA, FGB, FGG) were amplified by PCR followed by direct sequencing. Restriction endonuclease analysis was performed for the PCR products of the family members and 50 healthy donors to exclude gene polymorphism.

RESULTS

No Fg was detected in the plasma of the proband and her father by Clauss method, while low levels (< 0.02 g/L) were detected by immunonephelometry. A homozygous C to T mutation was found in the two cases at nucleotide 3108 in exon 4 of FGA gene, resulting in a null mutation which encoded severely truncated alpha-chains owing to its premature termination at the Gln 150 codon. The C-->T mutation eliminated a unique recognition site for restriction enzyme RsaI. The PCR amplified fragments of the proband and her father could not be digested by RsaI, showing that they are homozygous. Her mother and some family members are heterozygous at this site since the fragment could partly be digested, while the same fragment of controls could be completely digested as expected.

CONCLUSION

The Gln (CAG)-->150stop (TAG) nonsense mutation in FGA gene is a novel genetic defect of congenital afibrinogenemia which, to our knowledge, has not been described before.

Congenital Hypofibrinogenemia in Pregnancy: Report of Two Cases and Review of the Literature

Fibrinogen abnormalities have been implicated in many adverse pregnancy outcomes, mainly spontaneous abortion, placental abruption, and postpartum hemorrhage. Two new cases of congenital hypofibrinogenemia in pregnancy are reported detailing their obstetric course and management. The relevant obstetric and hematologic literature is reviewed, including previous case reports and studies concerning the mechanisms of pregnancy complications. Suggestions for treatment guidelines and management strategies are detailed.

Expression and analysis of a split premature termination codon in FGG responsible for congenital afibrinogenemia: escape from RNA surveillance mechanisms in transfected cells

Congenital afibrinogenemia, the most severe form of fibrinogen deficiency, is characterized by the complete absence of fibrinogen. The disease is caused by mutations in 1 of the 3 fibrinogen genes FGG, FGA, and FGB, clustered on the long arm of human chromosome 4. The majority of cases are due to null mutations in the FGA gene although one would expect the 3 genes to be equally implicated. However, most patients studied so far are white, and therefore the identification of causative mutations in non-European families is necessary to establish if this finding holds true in all ethnic groups. In this study, we report the identification of a novel nonsense mutation (Arg134Xaa) in the FGG gene responsible for congenital afibrinogenemia in 10 patients from Lebanon. Expression studies in COS-7 cells demonstrated that the Arg134Xaa codon, which is encoded by adjacent exons (TG-intron 4-A) affected neither mRNA splicing nor stability, but led to the production of an unstable, severely truncated fibrinogen gamma chain that is not incorporated into a functional fibrinogen hexamer.

The molecular mechanisms of congenital hypofibrinogenaemia

Congenital hypofibrinogenaemia is characterized by abnormally low levels of fibrinogen and is usually caused by heterozygous mutations in the fibrinogen chain genes (alpha, beta and gamma). However, it does not usually result in a clinically significant condition unless inherited in a homozygous or compound heterozygous state, where it results in a severe bleeding disorder, afibrinogenaemia. Various protein and expression studies have improved our understanding of how mutations causing hypo- and afibrinogenaemia affect secretion of the mature fibrinogen molecule from the hepatocyte. Some mutations can perturb chain assembly as in the gamma153 Cys-->Arg case, while others such as the Bbeta Leu-->Arg and the Bbeta414 Gly-->Ser mutations allow intracellular hexamer assembly but inhibit protein secretion. An interesting group of mutations, such as gamma284 Gly-->Arg and gamma375 Arg-->Trp, not only cause hypofibrinogenaemia but are also associated with liver disease. The nonexpression of these variant chains in plasma fibrinogen is due to retention in the endoplasmic reticulum, which in turn leads to hypofibrinogenaemia.

Pregnancy-related thrombosis in a woman with congenital afibrinogenemia: a report of two successful pregnancies

We managed two pregnancies in a woman with congenital afibrinogenemia with increasing amounts of cryoprecipitate to achieve a pre-infusion fibrinogen level of 60 mg/dL. The first pregnancy resulted in placental abruption at 36 weeks, in spite of recent cryoprecipitate infusion. Both placentas showed infarction. Post-partum ovarian and renal vein thromboses complicated the second pregnancy. Mean FVIII (344%) and vWF Antigen (323%) were elevated prior to cryoprecipitate infusion, with mean post-infusion levels of 367% and 363%. The clearance of fibrinogen after cryoprecipitate infusion increased during the course of pregnancy. A paradoxical prothrombotic state with embolization may play a role in the observed complications of pregnancy.

Congenital hypofibrinogenemia

Congenital afibrinogenemia/hypofibrinogenemia is an extremely rare coagulation disorder. We describe a case of congenital hypofibrinogenemia in a 6-year female child, who presented with recurrent ecchymotic spots with no frank bleeding.

Hemopneumothorax associated with Marfan syndrome and congenital afibrinogenemia

In patients with afibrinogenemia who require operation, prophylaxis against bleeding is important. We report the case of a 14-year-old boy with Marfan syndrome and congenital afibrinogenemia in whom hemopneumothorax developed. Video-assisted thoracoscopic surgery was performed successfully under intravenous administration of fibrinogen and with careful monitoring of plasma fibrinogen level.