Abstract:

Objective To analyze the phenotype and gene mutation of a family with hereditary dysfibrinogenemia caused by FGG gene Ala315Gly missense mutation，and to investigate the correlation of missense mutation and hereditary dysfibrinogenemia. Methods The clinical data of proband and the family members from Jiaozhou Branch of Shanghai East Hospital of Tongji University in December 2021(8 subjects in 3 generations) were collected for coagulation phenotype determination. All the exon and flanking sequences of proband fibrinogen(Fib) genes were analyzed. Mutation sites were validated by reverse sequencing. The corresponding mutation sites of the family members were also determined by Sanger sequencing. Co-segregation analysis of mutations and phenotypes was performed by comparing pedigree sequencing and NCBI database. The conservative analysis of mutation site genes was performed，and the potential effect of mutation site on protein function was predicted by bioinformatics online analysis software. The spatial structure and intermolecular forces of proteins before and after mutation were analyzed. Results Proband Fib C activity was 0.97 g·L^-1. The Fib activity results of the mother，aunt and grandfather were all decreased. Except for prolonged thrombin time(TT)T in the mother，the coagulation phenotypes of the proband and the other family members were within the reference interval. Compared with healthy controls，the maximum thrombin-induced fibrin aggregation rate and the slope of aggregation curve were reduced in the proband and his mother，aunt and grandfather. The proband FGG(4q31|NM_000509.4) gene exon8：c.944C>G：p.(Ala315Gly) heterozygous missense mutation ACMG evidence level was pathogenic mutation，and the type of mutation site was newly discovered internationally. The mother，aunt and maternal grandmother of the patient were all heterozygotes of Ala315Gly，while the locus of the father，aunt，uncle and maternal grandfather was wild-type，and the FGG gene c.944C>G mutation was co-segregated from the phenotype of the proband in this family. The A315 site was highly conserved among homologous species. Bioinformatics online analysis software predicted that Ala315Gly mutation would affect Fib aggregation function. Protein model analysis showed that Ala315 formed hydrophobic interaction with the amino acid residues around Trp395，Thr397，Ala367 and Gly318，and the hydrophobic interaction disappeared after mutation. The mutation changed the free energy of the protein and reduced the stability of the protein. Conclusions Fib c.944C>G missense mutation can lead to the loss of hydrophobic interaction around amino acids，and can change the protein's free energy，reduce the stability of the spatial structure，and eventually lead to the occurrence of hereditary dysfibrinogenemia.

Key words: FGG gene, Missense mutation, Hereditary dysfibrinogenemia, Pedigree, Fibrinogen