A Chinese family with congenital Dysfibrinogenemia carries a heterozygous missense mutation in FGA: Concerning the genetic abnormality and clinical treatment

A familial study of a de novo FGG gene mutation causing congenital hypofibrinogenaemia and intervention during pregnancy and childbirth

To investigate the family line of a pregnant woman with congenital hypofibrinogenaemia due to a de novo mutation in the fibrinogen gamma (FGG) gene and experimentally explore its molecular pathological mechanisms. Peripheral blood specimens were collected from the proband and her family members for coagulation tests to assess their coagulation function. Whole exome sequencing was used to determine the gene mutation in the family lineage. SDS-PAGE was utilized to analyze the plasma of the proband and her mother for their congenital hypofibrinogenaemia. Structural distribution was analyzed by scanning electron microscopy. Molecular modeling was performed to predict the effect of mutation sites on fibrinogen structure and function. A de novo heterozygous mutation in the FGG gene was identified: c.702G > T, with a markedly prolonged thrombin time. The thromboelastography results showed that her fibrinogen function was essentially normal. LC-MS/MS showed no plasma or mutant chains in the plasma. Molecular modeling showed that this de novo mutation altered the structure of fibrinogen in the patient and her fibrinogen was heterogeneous in diameter and sparsely networked under electron microscopy. An intermittent infusion of 6 g of fibrinogen in the prenatal period of the proband brought the fibrinogen level of the patient to 2.13 g/L. No significant haemorrhage was detected between and after the caesarean section. The FGG gene NM_021870.3: c.702G > T (p.Trp234Cys) mutation is a de novo mutation, which is heterozygous in both the proband and her mother. It's the biogenetic basis for the pathogenicity of this congenital hypofibrinogenaemia family line.

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.

Misdiagnosis of a patient with congenital dysfibrinogenemia: A case report and literature review

Background

We reported a patient with congenital dysfibrinogenemia who was misdiagnosed and reviewed relevant literature, in order to discuss the methods to reduce misdiagnosis.

Methods

A 23‐year‐old pregnant woman was found to be with low fibrinogen in antenatal examination at another province teaching hospital, who was misdiagnosed to have hypofibrinogenemia. Fibrinogen infusion or cryoprecipitation was recommended if necessary. The patient came to our hospital for further diagnosis and treatment considering the safety of herself and the fetus. We examined the coagulation function and gene sequencing of the pregnant woman and her family members.

Results

Fibrinogen (Clauss method) was significantly reduced in the patient and her mother, while the level of fibrinogen (PT‐derived method) was normal. Thrombin time was prolonged. Heterozygous mutation site was found in exon 2 of the FGA gene, c.104G > A(p.Arg35His).

Conclusion

When the fibrinogen (Clauss method) is significantly reduced and the thrombin time is prolonged, PT‐derived method and the investigation of family coagulation function should be added, which can be used to diagnose and distinguish congenital dysfibrinogenemia from hypofibrinogenemia.

Dysfibrinogenemia-Potential Impact of Genotype on Thrombosis or Bleeding

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

Analysis of an Inherited Dysfibrinogenemia Pedigree Associated with a Heterozygous Mutation in the FGA Gene

OBJECTIVE

 This article aims to analyze the phenotype and genotype of an inherited dysfibrinogenemia pedigree associated with a heterozygous mutation in the FGA gene, and to investigate the pathogenesis of this disease.

CLINICAL PRESENTATION

 The proband of interest is a 29-year-old woman. She was in her 37 weeks of gestation. Routine coagulation tests showed low fibrinogen activity (0.91 g/L; normal range: 2.0-4.0 g/L) and normal fibrinogen antigen (FIB:Ag) level (2.09 g/L; normal range: 2.0-4.0 g/L).

TECHNIQUES

 The prothrombin time, activated partial thromboplastin time, thrombin time, and activity of plasma fibrinogen (FIB:C) were detected by the one-stage clotting method. The FIB:Ag, D-dimer, and fibrinogen degradation products were tested by the immunoturbidimetry method. To identify the novel missense mutation, fibrinogen gene sequencing and molecular modeling were performed. We used ClustalX-2.1-win and online bioinformatic software to analyze the conservation and possible effect of the amino acid substitution on fibrinogen.

RESULTS

 Phenotypic analysis revealed that the FIB:C of the proband was significantly reduced while the FIB:Ag was normal. Sequencing analysis detected a heterozygous C.2185G > A point mutation in the FGA gene (AαGlu710Lys). Bioinformatic and modeling analyses indicated that the mutation probably caused harmful effects on fibrinogen.

CONCLUSION

 The heterozygous mutation of Glu710Lys in the FGA gene was identified that could cause the reduction of the FIB structure stability and result in the dysfibrinogenemia.