[Phylogenetic analysis and pathogenesis study of a new deletion mutation causing inherited FⅩ deficiency]

Objective: To analyze the F10 gene mutations in a Chinese pedigree affected with the deficiency of the hereditary coagulation factor X (FX), resulting from a new deletion mutation, and to study the associated molecular pathogenesis. Methods: Next generation sequencing (NGS) was performed to screen the genetic mutations in the proband which were then verified by Sanger sequencing. The FX activity (FX∶C) of probands and their family members was detected using the blood clotting method, and the mutation sites of the family members were analyzed using Sanger sequencing. The pathogenicity of the mutation site was predicted by using the online bioinformatics software, Mutation Taster. The SWISS-MODEL software was used for stimulating the three-dimensional models of the wild-type and mutant proteins for analyzing the influence of the mutation site on the structure and function of the proteins, and for analyzing the difference between the catalytic residues of the wild-type and the mutant proteins. The level of the F10 gene mRNA was quantitatively analyzed by qRT-PCR (quantitative reverse transcription polymerase chain reaction) method by constructing plasmids, transfecting human embryonic kidney 293T cells (HEK 293T), and analyzing the splicing of the mutated site by RT-PCR method. The levels of FⅩ∶Ag in cell lysates and cell culture media (both inside and outside the cells) were detected by the ELISA (enzyme linked immunosorbent assay) method. Results: A medium-grade factor X deficiency with a 36.42% FⅩ∶C ratio was detected in the proband by the coagulation method. NGS analysis demonstrated a heterozygous deletion mutation in exon 8:c.902_919del (p.Ala301_Glu306del) in the proband. Sanger sequencing analysis indicated that some members of the family (mother and grandfather) were also carriers of the corresponding deletion mutation. Online bioinformatics software predicted the pathogenic nature of the c.902_919del mutation, with a pathogenic score of 0.999. The 3D protein structure model analysis indicated that the c.902_919del mutation resulted in the disappearance of a segment of β-fold in the protein structure, thereby shortening the preceding segment of the β-fold and a subsequent loss of hydrogen bonds between adjacent amino acids with no significant difference in the side chain conformation of the key catalytic residues compared to the wild-type. mRNA splicing analysis indicated the absence of alternative splicing changes in the mutation, and qRT-PCR results indicated the absence of a statistically significant difference between the mRNA levels of F10 gene and wild-type mRNA in cells expressing c.902_919del mutant. The ELISA results indicated that there was no statistically significant difference in the FX∶Ag levels of the mutant cell culture medium and the lysate. Conclusions: In this pedigree, the heterozygous mutation in exon 8 of F10 gene (c.902_919del, p.Ala301_Glu306del) caused the hereditary factor Ⅹ deficiency.