The fibrinogen FGG p.Gly242Glu: a rare mutation associated with hypofibrinogenemia

A missense variant in DGKG as a recessive functional variant for hepatic fibrinogen storage disease in Wagyu cattle

Hepatic fibrinogen storage disease (HFSD) was diagnosed in a 5-month-old Wagyu calf with a history of recurrent respiratory disease. It was characterized by lethargy, dehydration, acidemia, and increased liver enzyme activities. Histologically, disseminated hepatocytes were swollen and showed a single, sharply demarcated, faintly eosinophilic cytoplasmic inclusion with a ground-glass appearance, with the nucleus in an eccentric position. Cytoplasmic inclusions did not stain with the periodic acid-Schiff (PAS) reaction. Using a rabbit polyclonal antibody against fibrinogen, the cytoplasmic vacuoles in the hepatocytes stained intensely. Electron microscopy disclosed hepatocytes with membrane-bound cytoplasmic inclusions filled with fine granular material interspersed with a few coarse-grained electron-dense granules. A trio whole-genome sequencing approach identified a deleterious homozygous missense variant in DGKG (p.Thr721Ile). The allele frequency in 209 genotyped Wagyu was 7.2%. This is a report of a DGKG-related recessive inherited disorder in cattle and adds DGKG to the list of candidate genes for HFSD in other species.

Mutations Accounting for Congenital Fibrinogen Disorders: An Update

Fibrinogen is a complex protein that plays a key role in the blood clotting process. It is a hexamer composed of two copies of three distinct chains: Aα, Bβ, and γ encoded by three genes, FGA, FGB, and FGG, clustered on the long arm of chromosome 4. Congenital fibrinogen disorders (CFDs) are divided into qualitative deficiencies (dysfibrinogenemia, hypodysfibrinogenemia) in which the mutant fibrinogen molecule is present in the circulation and quantitative deficiencies (afibrinogenemia, hypofibrinogenemia) with no mutant molecule present in the bloodstream. Phenotypic manifestations are variable, patients may be asymptomatic, or suffer from bleeding or thrombosis. Causative mutations can occur in any of the three fibrinogen genes and can affect one or both alleles. Given the large number of studies reporting on novel causative mutations for CFDs since the review on the same topic published in 2016, we performed an extensive search of the literature and list here 120 additional mutations described in both quantitative and qualitative disorders. The visualization of causative single nucleotide variations placed on the coding sequences of FGA, FGB, and FGG reveals important structure function insight for several domains of the fibrinogen molecule.

A Novel Amino Acid Substitution, Fibrinogen Bβp.Pro234Leu, Associated with Hypofibrinogenemia Causing Impairment of Fibrinogen Assembly and Secretion

We identified a novel heterozygous variant, Bβp.Pro234Leu (fibrinogen Tokorozawa), which was suspected to be associated with hypofibrinogenemia. Therefore, we analyzed the assembly and secretion of this fibrinogen using Chinese hamster ovary (CHO) cells. To determine the impact on the synthesis and secretion of fibrinogen of the Bβp.P234L and γp.G242E substitutions, we established recombinant variant fibrinogen-producing CHO cell lines. Synthesis and secretion analyses were performed using an enzyme-linked immunosorbent assay (ELISA) and immunoblotting analysis with the established cell lines. In addition, we performed fibrin polymerization using purified plasma fibrinogen and in-silico analysis. Both Bβp.P234L and γp.G242E impaired the secretion and synthesis of fibrinogen. Moreover, immunoblotting analysis elucidated the mobility migration of the Bβγ complex in Bβp.P234L. On the other hand, the fibrin polymerization of fibrinogen Tokorozawa was similar to that of normal fibrinogen. In-silico analysis revealed that the Bβp.P234 residue is located in the contact region between the Bβ and γ chains and contacts γp.G242 residue. The present study demonstrated that the Bβp.P234L substitution resulted in hypofibrinogenemia by decreasing the assembly and secretion of fibrinogen. Therefore, there is a possibility that substitutions in the contact region between the Bβ and γ chains impact the assembly and secretion of fibrinogen.