A novel factor X mutation Cys81 by Arg and a reported factor VII polymorphism Arg353 replaced by Gln co-occured in a patient
Coagulation factor X and factor VII (FVII) are both very important components in blood coagulation. To study the molecular pathogenic mechanism of the inherited factor X and FVII deficiency, the factor X activity (FX:C) and FVII activity were tested with one-stage clotting methods. The factor X antigen and factor FVII antigen were tested with ELISA. All the exons, intron–exon boundaries and 5′,3′-flanking regions of F10 and F7 genes were amplified by PCR with direct sequencing. The ClustalX software was used to analyze the conservative property of the mutation sites. The PolyPhen-2 and Sorting Intolerant From Tolerant (SIFT) online bioinformatics softwares were taken to predict whether the point mutation could affect protein function. The software Swiss-pdb Viewer was brought to analyze the impact of mutations on the structure and function of the protein. The thrombin generation tests were applied to evaluate whether there were obstacles in producing thrombin about the mutant protein. The FX:C and FVII activity of the proband were reduced to 35 and 42%, and the factor X antigen and factor FVII antigen were decreased to 43 and 55%, simultaneously. Correspondingly, a FX:Cys81Arg (Cys81 by Arg) mutation and a FVII:Arg353 replaced by Gln polymorphism were detected in the proband. The Cys81 of factor X was conserved among homologous species, but the Arg353 of FVII was not. All softwares analysis results indicated protein features and structures might be affected by the mutation and the polymorphism. And the thrombin generation tests showed that the mutant protein had obstacles in thrombin generation. We identified a FX:Cys81Arg mutation and a FVII:Arg353 replaced by Gln polymorphism in the proband. And they accounted for the decrease of the activity and antigen of factor X and FVII. Of note, the Cys81Arg of factor X was first reported in the world.