Analysis of inherited dysfibrinogenemia pedigree associated with a heterozygous and deletion mutantion in the FGG gene

Abstract

Objective To analyze the phenotype and genotype of inherited dysfibrinogenemia pedigree associated with a novel heterozygous and deletion mutation in the FGG gene, and to investigate its molecular mechanism. Methods The clinical data were collected from the proband found at our hospital and her family members in April 2016.The activity plasma fibrinogen (Fg: C), activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT) were detected by coagulation method and the antigen plasma fibrinogen (Fg: Ag ), D-Dimer (D-D), fibrinogen degradation products (FDPs) were analyzed by immunoturbidimetry method. All of the exons and exon-intron boundaries of the genes of FGA, FGB and FGG with the fibrinogen(Fg) were amplified by PCR and followed by direct sequencing. And further verification were performed by cloning sequence and non-denatured polyacrylamide gel electrophoresis and silver staining. The conservatism of mutated gene locus were analyzed by ClustalX- 2.1-win. The change of the protein spatial structure and the intermolecular forces with mutation were analyzed by Pymol. Results The Fg: C of the proband was significantly reduced(0.30 g/L) and the Fg: Ag of the proband was normal (2.00 g/L). Their Fg: C were both significantly reduced and the Fg: Ag were both normal (0.42 g/L, 2.09 g/L & 0.47 g/L, 2.42 g/L, respectively), these were found in her mother and grandma. Genetic analysis revealed a novel heterozygous and deletion mutation with c. 944_c.952 delCCTTTGATG in exon 8 of FGG gene in the proband, predicting a heterozygous 289_291delAla, Phe, Asp mutation. The same mutations were carried by her mother and grandma, but her father and grandpa were normal. Homology analysis indicated that the Ala289, Phe290 and Asp291 were maintained highly conservative in homogenous species. Protein model analysis found that the original hydrogen bonds were disappeared when the deletion mutation happened with the Ala289, Phe290 and Asp291. Conclusion The heterozygous and deletion mutation with 289_291delAla, Phe, Asp in the γ chain of fibrinogen were identified that could cause the rearrangement of the Fg molecular space structure and the reduction of the structure stability, so the mutation probably underly the dysfibrinogenemia in this pedigree.(Chin J Lab Med, 2018, 41: 305-311) Key words: Afibrinogenemia; Pedigree; Loss of heterozygosity; Fibrinogen; Mutation, missense