One Hundred Years of Congenital Fibrinogen Disorders

[Clinical phenotypes and genotypes of congenital fibrinogen disorder: an analysis of 16 children]

OBJECTIVES

To investigate the clinical phenotypes and genotypes of children with congenital fibrinogen disorder (CFD).

METHODS

A retrospective analysis was conducted on the clinical data of 16 children with CFD. Polymerase chain reaction was used to amplify all exons and flanking sequences of the FGA, FGB, and FGG genes, and sequencing was performed to analyze mutation characteristics.

RESULTS

Among the 16 children, there were 9 boys (56%) and 7 girls (44%), with a median age of 4 years at the time of attending the hospital. Among these children, 9 (56%) attended the hospital due to bleeding events, and 7 (44%) were diagnosed based on preoperative examination. The children with bleeding events had a significantly lower fibrinogen activity than those without bleeding events (P<0.05). Genetic testing was conducted on 12 children and revealed a total of 12 mutations, among which there were 4 novel mutations, i.e., c.80T>C and c.1368delC in the FGA gene and c.1007T>A and C.1053C>A in the FGG gene. There were 2 cases of congenital afibrinogenemia caused by null mutations of the FGA gene, with relatively severe bleeding symptoms. There were 7 cases of congenital dysfibrinogenemia mainly caused by heterozygous missense mutations of the FGG and FGA genes, and their clinical phenotypes ranged from asymptomatic phenotype to varying degrees of bleeding.

CONCLUSIONS

The clinical phenotypes of children with CFD are heterogeneous, and the severity of bleeding is associated with the level of fibrinogen activity, but there is a weak association between clinical phenotype and genotype.

Reviewing the Rich History of Fibrin Clot Research with a Focus on Clinical Relevance

Fibrin, described on a single-lens microscopy for the first time by Malpighi in 1666 and named by de Fourcroy, has been extensively studied by biochemists, biophysicists, and more recently by clinicians who recognized that fibrin is the major component of most thrombi. Elucidation of key reactions leading to fibrin clot formation in the 1950s and 1960s grew interest in the clinical relevance of altered fibrin characteristics. Implementation of scanning electron microscopy to image fibrin clots in 1947 and clot permeation studies in the 1970s to evaluate an average pore size enabled plasma clot characterization in cohorts of patients. Unfavorably altered fibrin clot structure was demonstrated by Blombäck's group in coronary artery disease in 1992 and in diabetes in 1996. Fifteen years ago, similar plasma fibrin clot alterations were reported in patients following venous thromboembolism. Multiple myeloma was the first malignant disease to be found to lead to abnormal fibrin clot phenotype in the 1970s. Apart from anticoagulant agents, in 1998, aspirin was first shown to increase fibrin clot permeability in cardiovascular patients. The current review presents key data on the rich history of fibrin research, in particular, those that first documented abnormal fibrin clot properties in a variety of human disease states, as well as factors affecting fibrin phenotype.

Laboratory Testing for Fibrinogen Disorders: From Routine Investigations to Research Studies

Congenital and acquired fibrinogen disorders often have heterogeneous clinical phenotypes and are challenging from a laboratory perspective. Fibrinogen determination using the Clauss method remains the gold standard, while the reproducibility and significance of the thrombin time and the reptilase time are limited. Molecular testing for causative mutations in fibrinogen genes is now recommended to confirm the diagnosis of congenital fibrinogen disorders. Research assays are used to evaluate alterations to fibrin formation and properties of plasma and purified fibrinogen-derived clots, characterized by fiber thickness, the number of branches, and pore sizes. Fibrin clot permeability (permeation, porosity) using a hydrostatic pressure system represents the most commonly used method for evaluating fibrin network density. Reduced clot permeability, which denotes the reduced size of an average pore in the network, results in tighter fibrin networks, typically associated with impaired susceptibility to lysis, leading to a thrombotic tendency. Biophysical properties of fibrin clots are largely assessed using rheometry, with atomic force microscopy and nanorheology being increasingly used in disease states. Thromboelastography and thromboelastometry, a simple modification of rheometry, have been used, mainly in intensive care units, for more than 50 years. Given growing evidence for altered fibrin clot properties in diseases with elevated risk of venous and arterial thromboembolism and in some bleeding disorders, further work on standardization and validation of the assessment of fibrin clot characteristics is needed. This review summarizes the current methods used to evaluate fibrinogen abnormalities in both diagnostic and research laboratories.

Highly thrombogenic phenotype and impaired wound healing in a patient with congenital dysfibrinogenemia: case report

Background

Congenital fibrinogen disorders are classified based on both fibrinogen levels and the clinical phenotype. For dysfibrinogenemia, normal fibrinogen levels are typical.

Key Clinical Question

We highlight the importance of comprehensive thrombotic risk assessment, including lipoprotein a (Lp[a]) and hypertriglyceridemia in association with severe thrombosis and poor wound healing in dysfibrinogenemia.

Clinical Approach

We report the case of a 42-year-old male patient with a rare congenital thrombotic-related dysfibrinogenemia (fibrinogen Naples) and multiple thrombotic episodes throughout his life and an unhealing ankle wound. Despite all thrombotic episodes and surgery, the patient had undetectable D-dimer, suggestive of fibrinolytic defect, further supported by over 4-fold elevated Lp(a) levels. The last arterial thrombosis was preoperatively managed by plasma exchange, antithrombotics, and thereafter continued fibrinogen replacement therapy, under which the chronic wound has healed.

Conclusion

The combination of thrombogenesis, abnormal fibrinogen, and high Lp(a) levels is a clinical and research topic deserving more attention.

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.

Pitfalls in Coagulation Testing

Assays in the coagulation laboratory are affected by numerous variables. Variables which have impact on the test result can lead to incorrect results, and potentially to consequences for further diagnostic and therapeutic decisions made by the clinician. The interferences can be separated into three main groups: biological interferences, with an actual impairment of the patient's coagulation system (congenital or acquired); physical interferences, which usually occur in the pre-analytical phase; and chemical interferences, because of the presence of drugs (mainly anticoagulants) in the blood to be tested. This article discusses some of these interferences in seven instructive cases of (near) miss events as an approach to generate more attention to these issues.