title: Molecular defects in the factor X gene caused by novel heterozygous mutations IVS5+1G>A and Asp409del.
abstract: Factor X (FX) deficiency is a rare autosomal-recessive bleeding disorder caused by diverse mutations in the F10 gene. To investigate the molecular basis of severe FX deficiency in a mildly hemorrhagic patient, variants of the F10 gene were detected by sequencing. A missense mutation was analysed by in vitro expression and modelling analysis, and a splice mutation using ectopic transcript analysis. The levels of activity of FX (FX:C) were <1% in both intrinsic and extrinsic pathway assays and 1.71% in chromogenic assay, the level of FX antigen (FX:Ag) was 53.36% in the proband. Two novel heterozygous mutations (IVS5+1G>A and Asp409del) were identified in the F10 gene. Ectopic transcript expression combined with informative marker (heterozygous Asp409del) analysis of the splice mutation (IVS5+1G>A) revealed and confirmed that the transcript from the mutated allele was absent, likely caused by the nonsense-mediated mRNA decay pathway. In vitro expression analysis showed that the Asp409del mutant led to a loss of enzymatic activity rather than impaired expression. Molecular modelling analysis confirmed that the Asp409del mutant dramatically altered the conformation of the 185-189 loop and impaired binding of the loop to sodium ions (Na(+) ), diminishing the enzymatic activity of FXa. This is the first report to clarify the molecular mechanisms of two naturally occurring F10 gene variants that cause severe FX deficiency.
authors.affiliation: State Key Laboratory of Medical Genomics, Shanghai Institute of Hematology, Shanghai, China.
authors.forename: J W
authors.initials: JW
authors.lastname: Zhou
authors.forename: Q
authors.initials: Q
authors.lastname: Liang
authors.forename: Q
authors.initials: Q
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Xie
authors.forename: Q L
authors.initials: QL
authors.lastname: Ding
authors.forename: X F
authors.initials: XF
authors.lastname: Wang
authors.forename: X D
authors.initials: XD
authors.lastname: Xi
authors.forename: H L
authors.initials: HL
authors.lastname: Wang
mesh_terms: D000328:Adult; D000941:Antigens; D001483:Base Sequence; D004252:DNA Mutational Analysis; D005170:Factor X / Q000235:genetics* / Q000378:metabolism; D005171:Factor X Deficiency / Q000235:genetics* / Q000378:metabolism; D006579:Heterozygote; D006801:Humans; D008297:Male; D009154:Mutation; D010375:Pedigree
chemical_list: D000941:Antigens; C010515:factor X antigen; D005170:Factor X