Congenital Fibrinogen Disorders Research Articles

Congenital structural and functional fibrinogen disorders: a primer for internists.

Congenital qualitative and quantitative fibrinogen disorders represent heterogeneous rare abnormalities caused by mutations in one of the 3 genes encoding individual fibrinogen polypeptide chains, located on chromosome 4q28. It is estimated that congenital fibrinogen disorder accounts for 8% of rare coagulation factor deficiencies. Most of congenital fibrinogen disorders are suspected in individuals with bleeding tendency or coincidentally discovered, for instance prior to surgery. Fibrinogen disorders could be also found in patients with thrombotic events, impaired wound healing, and recurrent spontaneous abortions. Afibrinogenemia manifests as mild to severe bleeding, while hypofibrinogenemia is often asymptomatic. Dysfibrinogenemia, a qualitative fibrinogen disorder, is associated with bleeding, thrombosis, or with no symptoms. Recent recommendations issued by the International Society on Thrombosis and Haemostasis in 2018 do not encourage routine evaluation of thrombin time or other coagulation tests in patients with suspected congenital fibrinogen disorders, highlighting the value of fibrinogen antigen measurement and genetic analysis, added to the key finding, that is, reduced fibrinogen concentration determined with a coagulometric assay. The current review summarizes practical issues in diagnostic workup and clinical management of patients with afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia from a perspective of internists who may encounter patients with reduced fibrinogen concentration in everyday practice. Despite the fact that hematologists are in front line for the management of patients with bleeding tendency, internists should be aware of the clinical and laboratory findings in patients with inherited fibrinogen disorders including the risk of thromboembolism and management prior to invasive procedures.

Genetic and clinical characterization of congenital fibrinogen disorders in Polish patients: Identification of three novel fibrinogen gamma chain mutations

IntroductionCongenital fibrinogen disorders are poorly explored in Slavic populations. The aim of this study was to characterize the genetic background and clinical manifestations of fibrinogen disorders in the Polish case series. Materials and methodsIn 27 unrelated patients (mean [SD] age, 30.4 [19.2] years, 30% men) with fibrinogen concentration (von Clauss method) < 1.8 g/L, exons and intron-exon junctions of the fibrinogen alpha chain (FGA), fibrinogen beta chain (FGB), and fibrinogen gamma chain (FGG) genes were analyzed using polymerase chain reaction (PCR) amplification followed by sequencing. ResultsAt enrollment, 15 (55.6%) and 2 (7.4%) of patients experienced bleeding and thrombotic events, respectively, and the remainder were asymptomatic. The following congenital fibrinogen disorders were identified: 1A. afibrinogenemia, n = 1; 2A. severe hypofibrinogenemia, n = 2; 2B. moderate hypofibrinogenemia, n = 4; 2C. mild hypofibrinogenemia, n = 6; 3A. dysfibrinogenemia, n = 12; 3B. thrombotic related-dysfibrinogenemia, n = 1; 4C. mild hypodysfibrinogenemia, n = 1.Eight dysfibrinogenemic patients (62%) were carriers of hotspot mutations. Fifteen patients were heterozygous and one (afibrinogenemia) homozygous for known causative mutations. Three new heterozygous mutations were detected, all affecting splicing in FGG: fibrinogen Poznan II, a 177 bp deletion eliminating parts of intron 6 and exon 7 in a dysfibrinogenemic woman with recurrent bleeding; fibrinogen Zakopane, (intron 2 acceptor splice site) and fibrinogen Belchatow (intron 1 donor splice site), found in hypofibrinogenemic patients.During follow-up (median 60, interquartile range 10–60 months), bleeding episodes, mainly menorrhagia and easy bruising were reported in 15 (55.6%) patients. One thromboembolic event was observed. ConclusionThis study of the largest cohort of Slavic patients with congenital fibrinogen disorders has enabled the identification of 3 new FGG mutations and shows a high prevalence of bleeding manifestations with recurrences.

Spontaneous vulvar hematoma as a rare manifestation of congenital hypofibrinogenemia. Case report

Introduction: Congenital fibrinogen disorders are rare conditions in which there are quantitative and qualitative alterations of factor I; the vast majority of patients are asymptomatic.Case presentation: A 19-year-old female patient with a history of congenital hypofibrinogenemia presented with spontaneous vulvar hematoma along with hypotension, tachycardia, stupor and hematoma of 20cm in the right labium majus. On admission, the young woman had hemoglobin 6.6 g/dL, fibrinogen 74 mg/dL and prolonged clotting times. She received red blood cells transfusion and cryoprecipitates, followed by surgical drainage and intravenous fibrinogen replacement, adjusting the dose according to fibrinogen levels in plasma. The patient presented progressive improvement without hemorrhagic recurrence and fibrinogen levels within the target values until hospital discharge.Discussion: Afibrinogenemia and hypofibrin­ogenemia are part of the quantitative factor I disorders; in the first case, there is total absence of circulating fibrinogen, and in the second case the levels are below 150 mg/dL. Sponta­neous vulvar hematoma as a severe hemorrhagic manifestation is not frequent in symptomatic patients; its treatment is based on fibrinogen replacement in an individualized manner and surgical management when required.Conclusion: Hypofibrinogenemia is a rare dis­ease, and fibrinogen replacement is one of the mainstays of treatment.

Mutational Epidemiology of Congenital Fibrinogen Disorders.

Numerous mutations in FGA, FGB or FGG lead to congenital fibrinogen disorders (CFDs), but their epidemiology is not well characterized. The aim of this study was to evaluate the molecular epidemiology of CFD and to develop a genotyping strategy. Genetic data from 266 unrelated CFD patients genotyped at our laboratory and from a CFD open access database (n = 1,142) were evaluated. We developed a step-wise screening strategy for the molecular diagnosis of CFD and prospectively tested this strategy on 32 consecutive CFD probands. We identified 345 mutated alleles overall, among 187 heterozygous, 63 homozygous and 16 compound heterozygous individuals. Afibrinogenemia was almost always caused by null mutations (98.6%), mainly in FGA (85%). Hypofibrinogenemia was mainly caused by missense mutations of FGB or FGG (54.2%). Dysfibrinogenemia was almost always caused by heterozygous missense mutations (99.3%) in FGA and FGG. Hotspot mutations were prevalent among quantitative (33.1%) and qualitative fibrinogen disorders (71.1%). The mutational cluster at our laboratory was similar with that reported in the CFD open access database. The proposed step-wise genetic screening strategy proved efficient in both the development and validation samples for CFD: the screening of FGA exons 2, 4, 5 and FGG exon 8 and search for the 11 kb deletion of FGA led to the identification of approximately 80% of mutated alleles, including 15 new mutations. The described molecular epidemiology of CFD is complex. The proposed step-wise genetic screening strategy may provide an efficient way to identify causative mutations analysing a minimal number of exons.

Identification and characterization of novel mutations implicated in congenital fibrinogen disorders

Unlabelled Box IntroductionFibrinogen is a complex molecule comprised of two sets of Aα, Bβ, and γ chains. Fibrinogen deficiencies can lead to the development of bleeding or thromboembolic events. The objective of this study was to perform DNA sequence analysis of patients with clinical fibrinogen abnormalities, and to perform genotype‐phenotype correlations. Materials and MethodsDNA from 31 patients was sequenced to evaluate disease‐causing mutations in the three fibrinogen genes: FGA, FGB, and FGG. Clinical data were extracted from medical records or from consultation with referring hematologists. Fibrinogen antigen and functional (Clauss method) assays, as well as reptilase time (RT) and thrombin time (TT) were obtained for each patient. Molecular modeling was used to simulate the functional impact of specific missense variants on the overall protein structure. ResultsSeventeen mutations, including six novel mutations, were identified in the three fibrinogen genes. There was little correlation between genotype and phenotype. Molecular modeling predicted a substantial conformational change for a novel variant, FGG p.Ala289Asp, leading to a more rigid molecule in a region critical for polymerization and alignment of the fibrin monomers. This mutation is associated with both bleeding and clotting in the two affected individuals. ConclusionsRobust genotype‐phenotype correlations are difficult to establish for fibrinogen disorders. Molecular modeling might represent a valuable tool for understanding the function of certain missense fibrinogen mutations but those should be followed by functional studies. It is likely that genetic and environmental modifiers account for the incomplete penetrance and variable expressivity that characterize fibrinogen disorders.

Human Fibrinogen: Molecular and Genetic Aspects of Congenital Disorders.

Congenital fibrinogen disorders can be quantitative (afibrinogenemia, hypofibrinogenemia) or functional (dysfibrinognemia). To date, several genetic variants have been identified in individuals with fibrinogen disorders. The complexity of the fibrinogen molecules, formed by three non-identical chains and with a trinodal organization, renders the identification of molecular causes and of clinical and biochemical phenotypes very challenging. However, the acknowledgement of the type of molecular defect is crucial for a safer therapy, which is going to improve the clinical management of these patients. In this review, some aspects concerning molecular and clinical findings available on congenital fibrinogen disorders will be discussed.

Congenital hypodysfibrinogenemia associated with a novel deletion of three residues (γAla289_Asp291del) in fibrinogen.

Hypodysfibrinogenemia is the least frequently reported congenital fibrinogen disorder, characterized by both quantity and quality defects of fibrinogen. In this study, we investigated the molecular basis of hypodysfibrinogenemia in a Chinese family. Functional fibrinogen was measured by Clauss method, and the antigenic fibrinogen was measured by immunoturbidimetry assay. All the exons and exon-intron boundaries of fibrinogen genes (FGA, FGB and FGG) were analysed by direct DNA sequencing. To further evaluate its molecular and functional characterizations, fibrinogen was purified from the plasma of propositus, then SDS-PAGE, fibrin polymerization, clot lysis, and electron microscopy scanning were all performed. The propositus showed a slight decrease of immunologic fibrinogen (1.52g/L) but dramatically reduced functional fibrinogen (0.3g/L). DNA sequencing revealed a novel heterozygous CCTTTGATG deletion in the exon 8 of FGG, leading to the deletion of Ala289, Phe290, and Asp291 in fibrinogen γ-chain. The polymerization of the fibrinogen from the propositus was markedly impaired, with prolonged lag period and decreased final turbidity. The fibrinogen clottability showed a reduced fraction of participating clot formation. While the clot lysis showed normal. Scanning electron microscopy revealed that the fibers of the propositus were thicker than normal, with larger pores and curlier meshworks. We conclude that γAla289_Asp291del is responsible for the hypodysfibrinogenemia in this case.

Identification of Two Novel Fibrinogen Bβ Chain Mutations in Two Slovak Families with Quantitative Fibrinogen Disorders.

Congenital fibrinogen disorders are caused by mutations in one of the three fibrinogen genes that affect the synthesis, assembly, intracellular processing, stability or secretion of fibrinogen. Functional studies of mutant Bβ-chains revealed the importance of individual residues as well as three-dimensional structures for fibrinogen assembly and secretion. This study describes two novel homozygous fibrinogen Bβ chain mutations in two Slovak families with afibrinogenemia and hypofibrinogenemia. Peripheral blood samples were collected from all subjects with the aim of identifying the causative mutation. Coagulation-related tests and rotational thromboelastometry were performed. All exons and exon–intron boundaries of the fibrinogen genes (FGA, FGB and FGG) were amplified by PCR followed by direct sequencing. Sequence analysis of the three fibrinogen genes allowed us to identify two novel homozygous mutations in the FGB gene. A novel Bβ chain truncation (BβGln180Stop) was detected in a 28-year-old afibrinogenemic man with bleeding episodes including repeated haemorrhaging into muscles, joints, and soft tissues, and mucocutaneous bleeding and a novel Bβ missense mutation (BβTyr368His) was found in a 62-year-old hypofibrinogenemic man with recurrent deep and superficial venous thromboses of the lower extremities. The novel missense mutation was confirmed by molecular modelling. Both studying the molecular anomalies and the modelling of fibrinogenic mutants help us to understand the extremely complex machinery of fibrinogen biosynthesis and finally better assess its correlation with the patient’s clinical course.

Assessment of Selected ROTEM Parameters, Kinetics of Fibrinogen Polymerization and Plasmin Amidolytic Activity in Patients with Congenital Fibrinogen Defects.

Congenital fibrinogen disorders (CFD) are rare fibrinogen deficiencies which may be quantitative or functional. The clinical course of hypofibrinogenemia (hypoFI) or dysfibrinogenemia (dysFI) is unpredictable and cannot be determined by the application of standard hemostasis tests. The main aim of this study was to assess ROTEM parameters in CFD patients. Nine patients with CFD were studied. The fibrinogen concentration was measured functionally and antigenically. EXTEM, INTEM, FIBTEM and APTEM tests were used to measure selected ROTEM parameters, including maximum clot firmness (MCF). Fibrin plasma polymerization, clot lysis and plasmin amidolytic activity were determined by spectrophotometric methods. Incorporating the antigenic, ELISA method, to the diagnostic workup allowed the initial diagnosis to be switched from hypoFI to dysFI in 3/7 patients. MCF readings (the most important parameter describing fibrin polymerization capacity) were significantly lower in patients than in controls according to all ROTEM tests. Cases with hypoFI demonstrated markedly lower readings of MCF according to all ROTEM tests than cases with dysFI. All patients demonstrated disturbances of fibrin polymerization process assessed by turbidimetry. In contrast, no marked differences were identified between studied groups in reference to plasmin amidolytic activity. Our data suggests that ROTEM and fibrin plasma polymerization according to the turbidimetric method have a high sensitivity towards detection of different CFD. Although ROTEM MCF assessment may help discriminate patients with hypoor dysfibrinogenemia, this finding has to be confirmed on larger groups of patients.

Diagnosis of congenital fibrinogen disorders

Congenital fibrinogen disorders comprise quantitative disorders defined by a complete absence (afibrinogenemia) or by a decreased level (hypofibrinogenemia) of circulating fibrinogen and qualitative disorders characterized by a discrepancy between the activity and the antigenic levels of fibrinogen (dysfibrinogenemia and hypodysfibrinogenemia). The biological diagnosis is based on a standard haemostasis assessment. All the coagulation tests that depend on the formation of fibrin as the end point are affected; although in dysfibrinogenemia the specificity and sensitivity of routine test depend on reagent and techniques. A genetic exploration permits to confirm the diagnosis and may enhance the prediction of the patient's phenotype. Homozygous or composite heterozygous null mutations are most often responsible for afibrinogenemia while hypofibrinogenemic patients are mainly heterozygous carrier of an afibrinogenemic allele. Heterozygous missense mutations are prevalent in dysfibrinogenemia, with two hot spot localized in exon 2 of the FGA and in the exon 8 of the FGG. The correlation between phenotype and genotype has been identified in some fibrinogen variants, including six mutations clustered in exons 8 and 9 of the FGG leading to hypofibrinogenemia with hepatic inclusions of abnormal fibrinogen aggregates as well as a few mutations associated with an increase risk of thrombotic events. A familial screening and additional functional assays should be carried out when possible.

Can the phenotype of inherited fibrinogen disorders be predicted?

Congenital fibrinogen disorders are rare diseases affecting either the quantity (afibrinogenaemia and hypofibrinogenaemia) or the quality (dysfibrinogenaemia) or both (hypodysfibrinogenaemia) of fibrinogen. In addition to bleeding, unexpected thrombosis, spontaneous spleen ruptures, painful bone cysts and intrahepatic inclusions can complicate the clinical course of patients with quantitative fibrinogen disorders. Clinical manifestations of dysfibrinogenaemia include absence of symptoms, major bleeding or thrombosis as well as systemic amyloidosis. Although the diagnosis of any type of congenital fibrinogen disorders is usually not too difficult with the help of conventional laboratory tests completed by genetic studies, the correlation between all available tests and the clinical manifestations is more problematic in many cases. Improving accuracy of diagnosis, performing genotype, analysing function of fibrinogen variants and carefully investigating the personal and familial histories may lead to a better assessment of patients' phenotype and therefore help in identifying patients at increased risk of adverse clinical outcomes. This review provides an update of various tests (conventional and global assays, molecular testing, fibrin clot analysis) and clinical features, which may help to better predict the phenotype of the different types of congenital fibrinogen disorders.

Clinical Features and Management of Congenital Fibrinogen Deficiencies.

Congenital fibrinogen disorders are rare diseases affecting either the quantity (afibrinogenemia and hypofibrinogenemia) or the quality (dysfibrinogenemia) or both (hypodysfibrinogenemia) of plasmatic fibrinogen. Afibrinogenemia is often diagnosed at birth following prolonged umbilical cord bleeding and is characterized by spontaneous bleeding in all tissues, while hypofibrinogenemic patients are more often asymptomatic. Spontaneous spleen ruptures, painful bone cysts, cardiovascular events, and intrahepatic inclusions can complicate the clinical course of patients with quantitative fibrinogen disorders. Clinical manifestations of dysfibrinogenemia are very heterogeneous, from absence of symptoms to major bleeding or thrombosis, chronic thromboembolic pulmonary hypertension, and renal amyloidosis. Hypodysfibrinogenemic patients can suffer from both major bleeding and recurrent thrombosis. Pregnancy of women with congenital fibrinogen disorders is a high-risk situation. Owing to the absence of controlled randomized studies, clinical management is mainly based on expert consensus. For the treatment and/or the prevention of bleeding, plasma-derived fibrinogen concentrates are the optimal choice. Treatment of thrombosis may be challenging. More specifically, management strategies should be tailored to each patient, taking the personal and familial history of bleeding and thrombosis, the genotype, and the specific clinical situation into account.

Laboratory and Genetic Investigation of Mutations Accounting for Congenital Fibrinogen Disorders.

Congenital fibrinogen disorders are classified into two types of plasma fibrinogen defects: type I (quantitative fibrinogen deficiencies), that is, hypofibrinogenemia or afibrinogenemia, in which there are low or absent plasma fibrinogen antigen levels, respectively, and type II (qualitative fibrinogen deficiencies), that is, dysfibrinogenemia or hypodysfibrinogenemia, in which there are normal or reduced antigen levels associated with disproportionately low functional activity. These disorders are caused by mutations in the three fibrinogen-encoding genes FGA, FGB, and FGG. Afibrinogenemia is associated with mild to severe bleeding, whereas hypofibrinogenemia is often asymptomatic. For these quantitative disorders, the majority of mutations prevent protein production. However, in some cases, missense or late-truncating nonsense mutations allow synthesis of the mutant fibrinogen chain, but intracellular fibrinogen assembly and/or secretion are impaired. Qualitative fibrinogen disorders are associated with bleeding, thrombosis, or both thrombosis and bleeding, but many dysfibrinogenemias are asymptomatic. The majority of cases are caused by heterozygous missense mutations. Here, we review the laboratory and genetic diagnosis of fibrinogen gene anomalies with an updated discussion of causative mutations identified.

HYPOFIBRINOGENEMIA COMPLICATING PREGNANCY � CASE REPORT AND REVIEW OF LITERATURE

Congenital fibrinogen disorder may be either afibrinogenemia / hypofibrinogenemia / dysfibrinogenemia. Afibrinogenemia may present at birth as bleeding from umbilical cord. Patients with hypofibrinogenemia may present only during surgical intervention or during pregnancy. Pregnancy with this condition is associated with a very high incidence of abortion & abruption. Fibrinogen replacement can be done using either cryoprecipitate or fibrinogen concentrate. Successful pregnancies have been reported using cryoprecipitate & fibrinogen concentrate (FC). We report a woman with 6 abortions previously who was treated with fibrinogen replacement therapy & delivered a live child.

Cryoprecipitate: no longer the best therapeutic choice in congenital fibrinogen disorders?

Congenital abnormalities of fibrinogen are rare disorders classified as quantitative (afibrinogenemia and hypofibrinogenemia) or qualitative types (dysfibrinogenemia and hypodysfibrinogenemia). Fibrinogen is essential to haemostasis as the substrate for fibrin clot formation and also acts in primary haemostasis as a key ligand in platelet aggregation. Quantitative deficiency of fibrinogen can result in severe bleeding, or arterial and venous thromboembolism, and poor wound healing. Dysfibrinogenemia is characterized by functional abnormalities of fibrinogen, which may be asymptomatic (in 50% of cases), or cause bleeding (25%) or thrombosis (25%). Replacement of the deficient or abnormal fibrinogen with frozen plasma, cryoprecipitate, or fibrinogen concentrate has been found to be effective in practice in treating haemostatic complications of these disorders. Although cryoprecipitate is the most commonly used replacement material, pathogen-reduced fibrinogen concentrates have several advantages, most importantly a lower potential risk of viral transmission and standardized fibrinogen content allowing accurate dosing. They also avoid transfusing unwanted clotting factors, platelet microparticles and immunoglobulins, and can be administered rapidly without thawing. The use of fibrinogen concentrate to treat congenital fibrinogen disorders is strongly supported in principle and increasingly by practical experience and evidence.

Congenital Fibrinogen Disorders

Inherited disorders of fibrinogen affect either the quantity (afibrinogenemia and hypofibrinogenemia) or the quality (dysfibrinogenemia) of the circulating fibrinogen or both (hypodysfibrinogenemia). Most often, patients with congenital fibrinogen disorders suffer from a bleeding diathesis but paradoxically may undergo severe thrombotic episodes. Pregnancy loss is another common clinical complication. Even in specialized laboratories, the precise diagnosis of some fibrinogen disorders may be challenging. Characterization of the molecular defect(s) is important as it provides a more accurate diagnosis, may enable prenatal diagnosis, will help elaborate a diagnostic strategy, and may distinguish in some cases those patients at risk of thrombosis rather than bleeding. However, the phenotype-genotype correlation is not easy to establish, and global hemostasis assays may provide a better evaluation of the patient's hemostatic state. Replacement therapy is effective in treating bleeding episodes, but it is important to tailor individual treatments because the pharmacokinetics of fibrinogen after replacement therapy is highly variable among patients. Although the number of cases studied and identified mutations are already quite substantial, the collection and comparison of molecular, biochemical, and clinical data will continue to yield valuable information on the development and course of these diseases, as well as on the choice of the most appropriate treatments.

Treatment of congenital fibrinogen disorders

Background: The goal of the coagulation pathway is the conversion of fibrinogen to fibrin and formation of an insoluble clot. Although relatively rare, congenital fibrinogen disorders are interesting and pose several challenges that can serve as paradigms for many diseases. An impressive body of knowledge has accumulated recently, particularly thanks to international collaborative clinical and genetic studies allowing the molecular characterization of these disorders. However, apart from the possibility of developing safer fibrinogen concentrates and the availability of prenatal diagnosis, the basic therapeutic approach has changed little. Objective: We need to better understand the clinical phenotype of patients in order to administer fibrinogen preparations or other treatments more appropriately. Methods: We discuss current therapeutic options and others that could be available in the near future. Results/conclusion: Patients with congenital fibrinogen deficiencies require better predictive tests for clinical complications and more efficient and available fibrinogen concentrates. Global hemostasis tests in combination with routine assays could help to individually tailor therapeutic protocols.