Congenital Hypodysfibrinogenemia due to γ326Cys→Tyr Mutation: Third Ever-Described Case Associated with Recurrent Venous Thrombosis and COVID Vaccine.

INTRODUCTION: Congenital fibrinogen disorders are a heterogenous group of fibrinogen defects. CASE PRESENTATION: Here, we describe hypodysfibrinogenemia in a 33-year-old female patient with provoked recurrent deep vein thrombosis (DVT) diagnosed based on decreased functional and antigenic fibrinogen levels with a decreased functional/antigenic fibrinogen ratio. Definitive diagnosis of congenital hypodysfibrinogenemia is done by genotyping using whole-exome sequencing, which identified the γ326Cys→Tyr mutation combined with single-nucleotide polymorphisms: rs2070011 and rs2070018 in FGA and rs1049636 in FGG. Fibrin structure assays showed reduced maximum polymerization rate. The mother of the proband shares the same γ326Cys→Tyr mutation and experienced a provoked DVT. CONCLUSION: Our case with DVT is the third ever-described occurrence of the mutation γ326Cys→Tyr that is associated with hypodysfibrinogenemia. The mechanism by which this mutation induces thrombosis remains unknown. Due to the high recurrence risk of thrombosis, the patient was treated with long-term reduced dose of rivaroxaban (10 mg daily) as secondary prophylaxis.

Clinical phenotype and laboratory characteristics of 93 patients with congenital fibrinogen disorders from unrelated 36 families.

Background: Congenital fibrinogen disorders (CFDs) are rare bleeding disorders (RBDs) caused by mutations in 1 of the 3 fibrinogen genes (FGA, FGB, and FGG). Objectives: To investigate the clinical phenotype, laboratory features, diagnosis, treatment, and prognosis of CFDs. Methods: Clinical data of 93 subjects with CFDs identified from June 2018 to December 2023 were retrospectively analyzed. Results: Among the 93 patients, there were 46 males (49.5%) and 47 females (50.5%), with a median age of 23 years. Fifty-three of 93 (57%) subjects experienced bleeding, 3/93 (3.2%) experienced thrombosis, and 37/93 (39.8%) were asymptomatic. Females were more prone to experience bleeding (P < .0001). The 93 patients exhibited prolonged thrombin time, significantly decreased fibrinogen activity (Fg:C), and normal or decreased fibrinogen antigen. The 93 patients included 3 with hypofibrinogenemia, 16 with hypodysfibrinogenemia, and 74 with dysfibrinogenemia. Among the 53 patients with bleeding, bleeding episodes were identified in 3.8% (2/53), 20.8% (11/53), and 75.5% (40/53) patients with hypofibrinogenemia, hypodysfibrinogenemia, and dysfibrinogenemia, respectively. Genetic analysis was performed on 22 cases from 8 pedigrees, revealing 10 mutations, including 1 novel splice mutation. Twenty-eight (30.1%) subjects received replacement therapy to treat or prevent bleeding, consisting of 8 fresh frozen plasma transfusions, 3 packing and suture treatment, and 61 fibrinogen infusions. Conclusion: Most patients with CFDs have mild or no bleeding symptoms. Fg:C combined with fibrinogen antigen and pedigree investigation can improve the feasibility and accuracy of diagnosis of CFDs. The severity of bleeding symptoms was negatively correlated with Fg:C.

A novel missense mutation (FGG c.1168G > T) in the gamma chain of fibrinogen causing congenital hypodysfibrinogenemia with bleeding phenotype.

BACKGROUND: Fibrinogen plays pivotal roles in multiple biological processes. Genetic mutation of the fibrinogen coding genes can result in congenital fibrinogen disorders (CFDs). We identified a novel heterozygous missense mutation, FGG c.1168G > T (NCBI NM_000509.6), and conducted expression studies and functional analyses to explore the influence on fibrinogen synthesis, secretion, and polymerization. METHODS: Coagulation tests were performed on the patients to detect the fibrinogen concentration. Whole-exome sequencing (WES) and Sanger sequencing were employed to detect the novel mutation. Recombinant fibrinogen-producing Chinese hamster ovary (CHO) cell lines were built to examine the recombinant fibrinogen synthesis and secretion by western blotting and enzyme-linked immunosorbent assay (ELISA). The functional analysis of fibrinogen was performed by thrombin-catalyzed fibrin polymerization assay. In silico molecular analyses were carried out to elucidate the potential molecular mechanisms. RESULTS: The clinical manifestations, medical history, and laboratory tests indicated the diagnosis of hypodysfibrinogenemia with bleeding phenotype in two patients. The WES and Sanger sequencing revealed that they shared the same heterozygous missense mutation, FGG c.1168G > T. In the expression studies and functional analysis, the missense mutation impaired the recombinant fibrinogen's synthesis, secretion, and polymerization. Furthermore, the in silico analyses indicated novel mutation led to the hydrogen bond substitution. CONCLUSION: The study highlighted that the novel heterozygous missense mutation, FGG c.1168G > T, would change the protein secondary structure, impair the "A: a" interaction, and consequently deteriorate the fibrinogen synthesis, secretion, and polymerization.

Congenital fibrinogen disorders: Strengthening genotype-phenotype correlations through novel genetic diagnostic tools.

Congenital fibrinogen disorders or CFDs are heterogenous, both in clinical manifestation and array of culprit molecular lesions. Correlations between phenotype and genotype remain poorly defined. This review examines the genetic landscape discovered to date for this rare condition. The question of a possible oligogenic model of inheritance influencing phenotypic heterogeneity is raised, with discussion of the benefits and challenges of sequencing technology used to enhance discovery in this space. Considerable work lies ahead in order to achieve diagnostic and prognostic precision and subsequently provide targeted management to this complex cohort of patients.

A Quest to Find the Aetiology of Pulmonary Embolism Beyond the Common: A Case of Dyshypofibrinogenemia Presenting as Pulmonary Embolism.

Hypodysfibrinogenemia-related thromboembolic disorder is a rarely encountered clinical entity. We present such a case of a 34-year-old lady with no known co-morbidities presenting to the accident and emergency unit with left-sided pleuritic chest pain associated with non-productive cough and breathlessness. Laboratory tests revealed fibrinogen level of 0.42 g/l (1.5-4g/l) with prolonged prothrombin time (PT), activated partial thromboplastin time (aPTT) along with elevated d-dimer, N-terminal pro-B-type natriuretic peptide (NT-proBNP), and troponin. CT pulmonary angiogram (CTPA) found bilateral pulmonary embolism with right heart strain. Functional/antigenic fibrinogen ratio was 0.38. Genetic testing eventually revealed a heterozygous missense mutation in exon 8-p.1055G>C; p.Cys352Ser in the sequencing of the fibrinogen gene FGG (gamma chain) confirming the diagnosis of dyshypofibrinogenemia. She was treated with anticoagulants with fibrinogen replacement therapy and later discharged on apixaban.

Two Novel Heterozygous Mutations (p.γPhe230Val and p.AαAsn839Thr) Cause Hereditary Hypodysfibrinogenemia in Two Chinese Independent Families.

The objective of this study was to explore the molecular defects in two Chinese families with hypodysfibrinogenemia. The coagulation method and immunoturbidimetric method were used to detect plasma fibrinogen activity and plasma fibrinogen antigen. The fibrinogen genes were amplified by PCR, and suspected mutations were confirmed by reverse sequencing. Bioinformatics and model analysis were used to study the conservatism and harm of the mutations. Study showed that the Fg:C and Fg:Ag of the probands of the two families were reduced, respectively, to 0.80g/L, 0.92g/L and 1.35g/L, 1.42g/L; gene analysis revealed that the proband 1 had a heterozygous missense mutation of c.688T>G (p.γPhe230Val) in exon 7 of the FGG gene; the c.2516A>C (p.AαAsn839Thr) heterozygous missense mutation in exon 6 of the FGA gene was got by the proband 2. These mutations found in this study might be related to the hypodysfibrinogenemia.

Congenital (hypo-)dysfibrinogenemia and bleeding: A systematic literature review.

Ranging from bleeding to thrombosis, the clinical features of congenital fibrinogen qualitative disorders, including dysfibrinogenemia and hypodysfibrinogenemia, are highly heterogeneous. Although the associations between some specific fibrinogen mutations and the thrombotic phenotypes have been well elucidated, the underlying mechanism between fibrinogen variants and bleeding events remains underestimated. After systematically reviewing the literature of (hypo-)dysfibrinogenemia patients with bleeding phenotypes, we identified several well-characterized bleeding-related fibrinogen variants in those patients. Several possible pathomechanisms are proposed to explain the genotype-phenotype associations: 1, mutations in the NH2-terminal portion of the Aα chain hamper fibrinogen fitting into the active site cleft of thrombin and drastically slow the conversion of fibrinogen into monomeric fibrin; 2, mutations adding new N-linked glycosylation sites introduce bulky and negatively charged carbohydrate side chains and undermine the alignment of fibrin monomers during polymerization; 3, mutations generating unpaired cysteine form extra disulfide bonds between the abnormal fibrinogen chains and produce highly branched and fragile fibrin networks; 4, truncation mutations in the fibrinogen αC regions impair the lateral fibril aggregation, as well as factor XIII crosslinking, endothelial cell and platelet binding. These established relationships between specific variants and the bleeding tendency will help manage (hypo-)dysfibrinogenemia patients to avoid adverse bleeding outcomes.

Fibrinogen Deficiency with Thrombotic Manifestations.

Fibrinogen deficiencies are very rare. Qualitative fibrinogen deficiencies (dysfibrinogenaemia and hypodysfibrinogenemia) are functional disorders that can present with both haemorrhagic symptoms and with thrombotic phenomena as unique and paradoxical manifestation. We present the case of a 77-year-old man being investigated for a partially thrombosed abdominal aortic aneurysm as well as an ischaemic stroke 20 years previously. Basic coagulation tests were normal but extended tests revealed a lengthened thrombin time (TT) combined with a significant drop in fibrinogen concentration measured with the Clauss assay and by nephelometry. After secondary fibrinogen deficiencies were ruled out, a heterozygous variant in the FGG gene was detected by next-generation sequencing, and congenital hypodysfibrinogenemia was diagnosed. Acenocumarol was initiated and no new thrombotic or haemorrhagic events had occurred after a year of follow-up. In almost 25% of cases, thrombotic events may be the only clinical manifestation of functional fibrinogen deficiencies. They are a rare cause of thrombophilia, and are probably underdiagnosed due to normal standard coagulation test results as well as a possible absence of haemorrhagic events. Consequently, a TT test (an initial 'rule out' test) should be requested in order to promptly identify these patients. Moreover, discrepancies in derived and Clauss fibrinogen test results should suggest a functional disorder. Finally, new coagulation techniques based on the functional characterization of clot formation, such as ROTEM or thrombin generation assay, could help characterize these entities and suggest new therapeutic approaches. LEARNING POINTS: Functional fibrinogen deficiencies can present with thrombotic manifestations only, and are a rare and probably underdiagnosed cause of thrombophilia.Thrombin time is a highly sensitive test to rule out other conditions as aPTT and PT results may be within normal ranges, especially in functional deficiencies.Discrepancies between derived and Clauss fibrinogen findings, fibrinogen protein measurements and the use of new techniques (ROTEM or thrombin generation) are important for correct approach.

Pseudohomozygous dysfibrinogenemia.

Hypodysfibrinogenemia (HD) is a heterogeneous disorder in which plasma fibrinogen antigen and function are both reduced but discordant. This report addresses the key clinical question of whether genetic analysis enables clinically useful subclassification of patients with HD. We report a new case and identify a further eight previously documented cases that have the laboratory features of HD but biallelic inheritance of quantitative and qualitative fibrinogen gene variants. The cases displayed both bleeding and thrombosis and sometimes had undetectable fibrinogen activity. In all cases, the predicted effect of the coinherited variants is reduced levels of circulating fibrinogen that is all dysfunctional. We propose the term pseudohomozygous dysfibrinogenemia for this subtype of recessively inherited HD that is distinct from the more commonly recognized monoallelic HD caused by a single fibrinogen gene variant.

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.

Novel variant fibrinogen γp.C352R produced hypodysfibrinogenemia leading to a bleeding episode and failure of infertility treatment.

INTRODUCTION: We identified a patient with a novel heterozygous variant fibrinogen, γp.C352R (Niigata II; N-II), who had a bleeding episode and failed infertility treatment and was suspected to have hypodysfibrinogenemia based on low and discordant fibrinogen levels (functional assay 0.33 g/L, immunological assay 0.91 g/L). We analyzed the mechanism of this rare phenotype of a congenital fibrinogen disorder. MATERIALS AND METHODS: Patient plasma fibrinogen was purified and protein characterization and thrombin-catalyzed fibrin polymerization performed. Recombinant fibrinogen-producing Chinese hamster ovary (CHO) cells were established and the assembly and secretion of variant fibrinogen analyzed by ELISA and western blotting. RESULTS: Purified N-II plasma fibrinogen had a small lower molecular weight band below the normal γ-chain and slightly reduced fibrin polymerization. A limited proportion of p.C352R fibrinogen was secreted into the culture medium of established CHO cell lines, but the γ-chain of p.C352R was synthesized and variant fibrinogen was assembled inside the cells. CONCLUSION: We demonstrated that fibrinogen N-II, γp.C352R was associated with markedly reduced secretion of variant fibrinogen from CHO cells, that fibrin polymerization of purified plasma fibrinogen was only slightly affected, and that fibrinogen N-II produces hypodysfibrinogenemia in plasma.

Extension of the Human Fibrinogen Database with Detailed Clinical Information-The αC-Connector Segment.

Fibrinogen, an abundant plasma glycoprotein, is involved in the final stage of blood coagulation. Decreased fibrinogen levels, which may be caused by mutations, are manifested mainly in bleeding and thrombotic disorders. Clinically relevant mutations of fibrinogen are listed in the Human Fibrinogen Database. For the αC-connector (amino acids Aα240-410, nascent chain numbering), we have extended this database, with detailed descriptions of the clinical manifestations among members of reported families. This includes the specification of bleeding and thrombotic events and results of coagulation assays. Where available, the impact of a mutation on clotting and fibrinolysis is reported. The collected data show that the Human Fibrinogen Database reports considerably fewer missense and synonymous mutations than the general COSMIC and dbSNP databases. Homozygous nonsense or frameshift mutations in the αC-connector are responsible for most clinically relevant symptoms, while heterozygous mutations are often asymptomatic. Symptomatic subjects suffer from bleeding and, less frequently, from thrombotic events. Miscarriages within the first trimester and prolonged wound healing were reported in a few subjects. All mutations inducing thrombotic phenotypes are located at the identical positions within the consensus sequence of the tandem repeats.

Identification and characterization of novel mutations in Chinese patients with congenital fibrinogen disorders.

INTRODUCTION: Congenital fibrinogen disorders are characterized by heterogeneous clinical manifestations with mutations in the fibrinogen gene cluster. We aimed to describe the molecular genetics and clinical manifestations of fibrinogen abnormalities and perform genotype-phenotype correlations. MATERIALS AND METHODS: Genetic analysis of fibrinogen genes was performed by direct sequencing. The effect of the specific missense variants on fibrinogen structure and function was analyzed using PROVEAN and PolyPhen-2 algorithms and was predicted by protein modeling. RESULTS: Thirteen mutations, including five novel mutations, were identified in the three fibrinogen genes. There was poor correlation between genotypes and phenotypes. All but one of the novel mutations in subjects were predicted to be deleterious. Protein modeling predicted that multiple ienteractions with surrounding residues for novel variants were likely to result in congenital fibrinogen disorders. CONCLUSION: This study in a relatively large cohort of Chinese patients with congenital fibrinogen disorders enabled the identification of five new fibrinogen missense mutations. In silico modeling may represent a valuable tool for understanding amino acid residues from novel variants leading to congenital fibrinogen disorders, but it should be followed by functional studies. Clinical presentation of fibrinogen disorders was variable, possibly due to genetic and environmental modifiers.

Fibrin clot properties to assess the bleeding phenotype in unrelated patients with hypodysfibrinogenemia due to novel fibrinogen mutations.

Congenital hypodysfibrinogenemia is a rare fibrinogen disorder, defined by decreased levels of a dysfunctional fibrinogen. We present the functional and structural characterization of two new fibrinogen variants. A duplication of 32 bases in FGA exon 5, p.Ser382GlyfsTer50 was identified in a patient (P1) with history of hemoptysis and traumatic cerebral bleeding. A missense mutation in FGG exon 8, p.Ala353Ser was identified in two siblings (P2 and P3) with tendency to bruising and menorrhagia. Fibrin polymerization was studied in plasma and in purified fibrinogen by turbidimetry. Fibrin structure was studied by a permeability assay, laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). In both plasma and purified fibrinogen samples, all patients had an abnormal polymerization characterized by a decreased maximal absorption compared to controls. The permeation constant (Ks) was markedly increased in all patients: 31 ± 9 × 10-9 cm2 in P1, and 20 ± 0.1 × 10-9 cm2 in P2 and P3, compared to 6 ± 2 × 10-9 cm2 in the control (p < 0.05). The presence of very large pores that accounts for the increased Ks was confirmed by LSCM and SEM patients' clots images. By SEM, the patients' fibrin fibers diameters were thicker: 90 ± 25 nm in P1, 162 ± 64 nm in P2 and 132 ± 46 nm in P3 compared to 74 ± 25 nm in control (p < 0.0001). In conclusion, both new causative fibrinogen mutations altered clot structure by forming thick fibers, diminishing fiber branching, and increasing pore filling space. These structural changes to clots explain the patients' bleeding phenotypes.

Congenital fibrinogen disorder with a compound heterozygote possessing two novel FGB mutations, one qualitative and the other quantitative.

INTRODUCTION: Congenital fibrinogen disorders result from genetic mutations in FGA, FGB, or FGG resulting in quantitative fibrinogen deficiencies (afibrinogenemia or hypofibrinogenemia) or qualitative fibrinogen deficiencies (dysfibrinogenemia). Hypodysfibrinogenemia sharing features with hypo- and dysfibrinogenemia is rare. We performed genetic and functional analyses of a 31-year-old woman with suspected hypodysfibrinogenemia. MATERIALS AND METHODS: Functional and antigenic fibrinogen values of patient were 1.05 and 1.24 g/L, respectively. DNA sequence and western blotting analyses for plasma fibrinogen were performed. A minigene incorporating the mutational region was transfected into a Chinese hamster ovary cell line (CHO), and reverse transcription products were analyzed. Assembly and secretion were examined using the recombinant variant fibrinogen. We purified the patient's plasma fibrinogen and analyzed thrombin-catalyzed fibrin polymerization (TCFP). RESULTS AND CONCLUSIONS: DNA sequencing revealed compound heterozygous nucleotide mutations with FGB 35 bp c.1245-17_1262 or -16_1263 del and FGB c.510T>A (resulting in Bßp.N170K substitution) on different alleles. We did not detect shortened Bß-chain peptides in the plasma using western blotting analysis. A minigene incorporating the deletion DNA showed two aberrant mRNA products. The secretion of Bßp.N170K-fibrinogen-CHO was almost same as normal Bß-fibrinogen-CHO. TCFP of plasma Bßp.N170K fibrinogen was slightly lower than that of normal plasma fibrinogen. Aberrant splicing products derived from the 35 bp deletion caused hypofibrinogenemia due to nonsense-mediated mRNA decay and suggested the presence of only Bßp.N170K fibrinogen in patient's plasma. Bßp.N170K caused dysfibrinogenemia due to a delay in lateral aggregation. These findings demonstrated that these mutations respectively affected the fibrinogen quality and quantity, resulting in hypodysfibrinogenemia.

Heterozygous variant fibrinogen γA289V (Kanazawa III) was confirmed as hypodysfibrinogenemia by plasma and recombinant fibrinogens.

INTRODUCTION: Congenital fibrinogen disorders are classified as afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia. However, difficulties are associated with discriminating between dysfibrinogenemia, hypofibrinogenemia, and hypodysfibrinogenemia using routine analyses. We previously reported a heterozygous variant fibrinogen (γA289V; Kanazawa III) as hypodysfibrinogenemia; however, the same variant had previously been described as hypofibrinogenemia. To clarify the production of γA289V fibrinogen, we expressed recombinant γA289V (r-γA289V) fibrinogen and compared it with wild-type (WT) and adjacent recombinant variant fibrinogens. METHODS: Target mutations were introduced into a fibrinogen γ-chain expression vector by site-directed mutagenesis, and the vector was then transfected into Chinese hamster ovary cells to produce recombinant fibrinogen. Fibrinogen was purified from the plasma of the proposita, and culture media and fibrinogen functions were analyzed using fibrin polymerization, plasmin protection, and FXIIIa-catalyzed fibrinogen cross-linking. RESULTS: The fibrinogen concentration ratio of the culture media to cell lysates was markedly lower for r-γA289V fibrinogen than for WT. Because the secretion of recombinant γF290L (r-γF290L) fibrinogen was similar to WT, we compared r-γF290L fibrinogen functions with WT. The fibrin polymerization of Kanazawa III plasma (K-III) fibrinogen was significantly weaker than normal plasma fibrinogen. Moreover, K-III fibrinogen showed a markedly reduced "D:D" interaction. However, all functions of r-γF290L fibrinogen were similar to WT. An in silico analysis confirmed the above results. CONCLUSION: The present results demonstrated that γA289 is crucial for the γ-module structure, and the γA289V substitution markedly reduced fibrinogen secretion. Moreover, K-III fibrinogen showed markedly reduced fibrin polymerization and "D:D" interactions. γA289V fibrinogen was confirmed as hypodysfibrinogenemia.

Combined Congenital Hypodysfibrinogemia and Factor XI Deficiency in a Chinese Family.

Both congenital hypodysfibrinogenemia and factor XI deficiency are rare coagulopathies caused by mutations within the fibrinogen and F11 genes, respectively. To investigate the pathogenesis of combined congenital hypodysfibrinogenemia with factor XI (FXI) deficiency in a Chinese family, coagulation assays, FXI activity (the 1-stage method), fibrinogen activity (the Clauss method), and antigen (prothrombin time [PT]-derived method) were performed. The sequences of fibrinogen genes and F11 were amplified by PCR and analyzed by direct sequencing. The proband as well as his grandmother, father, aunt, and sister showed a low plasma concentration of fibrinogen measured by the Clauss method and a slightly decreased result by the PT-derived method; finally, c.1097A>G in exon 8 of FGG was detected in the pedigree, which caused His340Arg mutation. His grandfather had a slightly prolonged activated partial thromboplastin time (APTT) due to low FXI activity. FXI deficiency was a compound heterozygote inherited with missense mutations of c.434A>G in exon 5 as well as c.1253G>T in exon 11 which caused HGV p.His145Arg and Gly400Val mutations, respectively. The grandfather had no qualitative or quantitative defect in fibrinogen. The proband and his father and aunt had c.434A>G at the exon 5 mutation site and no decrease in FXI activity. His mother had no fibrinogen or F11 gene mutations. Plasma fibrin polymerization was delayed. The proband in our study showed typical changes of congenital hypodysfibrinogemia in the clotting analyses with delayed fibrin polymerization, but although he was a heterozygous carrier of the c.434A>G variant in the F11 gene, he had no decrease in FXI activity and no bleeding tendency, thus questioning the pathogenicity of the identified variant in the F11 gene. To our knowledge, this is the first report of a case of combined hypodysfibrinogenemia and FXI deficiency confirmed by molecular genetic tests.

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

INTRODUCTION: Congenital 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 METHODS: In 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. RESULTS: At 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. CONCLUSION: This 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.

Fibrinogen Columbus II: A novel c.1075G>T mutation in the FGG gene causing hypodysfibrinogenemia and thrombosis in an adolescent male.

Hypodysfibrinogenemia, the least frequently reported congenital fibrinogen disorder is characterized by low circulating levels of a dysfunctional protein, and is associated with phenotypic features of both hypo- and dysfibrinogenemia. Herein, we report an adolescent male with unprovoked venous thromboembolism and hypodysfibrinogenemia. Patient had recurrent, progressive thrombosis despite therapeutic anticoagulation with both low molecular weight heparin and warfarin. He had clinical and radiological improvement after transition to a direct thrombin inhibitor. Sequencing of the FGG gene identified a novel heterozygous mutation, c.1075G>T. Structural visualization of the identified variant was pursued and suggested that the mutation likely destabilizes the Ca2+ -binding site of fibrinogen resulting in pathogenicity.