Identification and characterization of novel mutations implicated in congenital fibrinogen disorders

Abstract

Essentials Fibrinogen Disorders are characterized by variable expressivity.Patients with fibrinogen disorders can present with bleeding, thrombosis, or both.As previously reported, genotype‐phenotype correlations are difficult to establish.Molecular modeling may help to further understand the effects of mutations on the mature fibrinogen protein. 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 Methods DNA 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.

Loss of fibrinogen in zebrafish results in an asymptomatic embryonic hemostatic defect and synthetic lethality with thrombocytopenia

“…Given the similarities between human and zebrafish fibrinogen deficiencies, we were able to use our model to discriminate the functional consequences of human mutations, finding that M1V and Y809C were unable to rescue the hemostatic defect. M1V is a novel mutation that has been recently identified in patients and here we confirm it in vivo as a pathological mutation. Surprisingly, two cysteine substitutions, C55G (Fibrinogen La Seyne and Fibrinogen Quimper) and C64Y (Fibrinogen Marseilles II), were able to rescue fga − / − mutants despite the fact that both positions are highly conserved and patients with these mutations are hypofibrinogenemic (activity levels down to 20–50% of the lower limit of the normal range ).…”

Molecular and clinical profile of congenital fibrinogen disorders in Iran, identification of two novel mutations

“…The p.Trp52Ter nonsense mutation was reported in an asymptomatic heterozygote and one patient with hypodysfibrinogenemia (p.Trp52Ter/p. Arg16Cys) 30 . In our study, mutational screening led to the identification of the p.Trp52Ter nonsense mutation in three patients with afibrinogenemia (subjects 2, 3, and 4) with variable bleeding tendency (Table 2).…”

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

“…We attributed the discrepancy between the two families to the fact that the amount of γA289V fibrinogen in plasma was too low and it was inadequate for the mass analysis sensitivity. In addition, because the novel heterozygous mutation, γA289D, was recently reported as dysfibrinogenemia, the γA289 residue is important for fibrinogen function. The heterozygous γG292V fibrinogens, Baltimore I and St. Gallen I, have been reported as dysfibrinogenemia and hypodysfibrinogenemia, respectively .…”