Objective: To analyze the phenotype and genotype of two Chinese family with inherited dysfibrinogenemia and the molecular pathogenic mechanism.
Methods: In the probands and their family members, coagulation routine, fibrinogen activity (Fg: A) and fibrinogen antigen (Fg: Ag) were detected. To find the mutation and exclude single nucleotide polymorphisms, all the exons and exons-intron boundaries of fibrinogen genes (FGA, FGB and FGG) were amplified by Ploymerase Chain Reaction (PCR), then sequenced. Bioinformatics prediction softwares were used to predict and score the change of function caused by the variant. PyMol were used to analyze the structure of protein caused by the variant. Clustal X software was used to analyze the conservation of the mutant amino acids.
Results: The thrombin time (TT) of the two was slightly prolonged and could not be corrected by protamine sulfate, and the fibrinogen activity was significantly reduced (1.25 g/L and 1.17 g/L), but the fibrinogen antigen content was normal, respectively (3.50 g /L and 3.81 g/L). Genetic analysis showed that both probands were heterozygous missense variants (FGB exon 7 c.1115T>A (p.Val372Glu)), both of which originated from the paternal line. The prediction results of the four bioinformatics softwares indicate that this variant could be disease causing. Clustal X software showed that Val372 is highly conserved among homologous species. Based on the guidelines of the American College of Medical Genetics and Genomics, c.1115T>A was predicted to be likely pathgenic (PM2+PP1+PP2+PP3+PP4). PyMol showed that the secondary structure and three-dimensional structure of fibrinogen protein were changed by p.Val372Glu variant.
Conclusion: Inherited dysfibrinogenemia of the probands maybe caused by variant of FGB c.1115 T>A (p.Val372Glu), and the variant was firstly reported.