Functional consequences of the Ser334-->Pro mutation in a human factor X variant (factor XMarseille)

Recurrence of a Phe31Ser mutation in the Gla domain of blood coagulation factor X, in unrelated Algerian families: a founder effect?

The presence of gene lesions in blood coagulation factor X (FX) was investigated in eight FX-deficient patients with severe bleeding symptoms, originating from five unrelated Algerian families (FX coagulant activity <1%, FX antigen ranging from 2% to 16%). A missense mutation (p.Phe31Ser) in the Gla domain was found in homozygous form for all patients but one, who is a compound heterozygote for the Phe31Ser mutation and for a non-sense mutation, Tyr130Term in EGF-2 domain. The haplotypes of FX alleles were determined by the following allelic variants located in the promoter: g.1323_1330delTTGTGA (A1/A2), g.1449T>C, g.1451C>A, upstream to exon 3: g.17257C>T and downstream to exon 3: g.17396A>C. The A1-C-A-T-C haplotype was found on each allele bearing the Phe31Ser mutation in the eight FX deficient patients contrasting with its low frequency (8%) in a control Algerian population (in which the Phe31Ser substitution was absent). The patients came from the same geographical area of Algeria (5/8 are certainly from Kabyle origin) and the haplotype analysis suggests a founder effect. Transient expression study reveals that, for the mutant FX-Phe31Ser, FX antigen level was 60% in conditioned media and 140% in cell lysates compared with the wild type FX. The partial retention and intracellular accumulation of the mutant FX might be due to impaired folding and/or conformational changes, and the discrepancies observed between the FX antigen level in COS-7 cell supernatant (60%) and in the patients plasma (2-16%) to an in vivo increased clearance of the secreted unstable FX mutant.

Genetic analysis of hereditary factor X deficiency in a French patient of Sri Lankan ancestry

We investigated a new family with cross-reactive material-positive factor X (FX) deficiency. The proband was an 11-year-old French girl from Sri Lanka with a tendency towards severe bleeding. The FX antigen level was 67%, although the activity with extrinsic pathway was 1 U/dl. The complete nucleotide sequences of all exons and exon/intron junctions of the patient's genomic DNA revealed a homozygous G <-- A substitution in exon 8, which would result in replacement of Gly366 with Ser. The proband is the first reported case of homozygote for the FX Gly366Ser mutation. Heterozygosity for Gly366Ser substitution was previously reported in a Japanese patient (FX Nagoya 2). We studied the functional consequences by expressing mutant FX Gly366Ser protein in HEK293 cells. FX Gly366Ser was secreted into the culture media at levels similar to wild-type FX; however, mutant FX activities were only 0.04, 1.05, and 0.75% of wild-type FX upon activation by the extrinsic system, the intrinsic system, and Russell's viper venom, respectively. Moreover, the activity of FX Gly366Ser was undetectable when analyzed with chromogenic-activated FX and thrombin generation assays. These data suggest that the Gly366Ser substitution would cause a major defect in function of the FX molecule.

One missense mutation in the factor X gene causing factor X deficiency--factor X Kanazawa

We investigated the molecular basis of factor X deficiency in a Japanese patient whose factor X activity and antigen level were 45% and 50% of normal control values, respectively. All exons and intron/exon junctions of the factor X gene were studied using a strategy combining polymerase chain reaction (PCR) amplification and nonradioactive single-strand conformational polymorphism (SSCP) analysis. Exon 5, containing the DNA fragment of the proband, showed aberrant migration by SSCP analysis. All exon-containing DNA fragments amplified by PCR were sequenced, and it was revealed that the proband was a heterozygote for a G --> A substitution in exon 5 of the factor X gene of the proband. This mutation predicts an amino acid replacement of arginine (Arg) for glycine (Gly) at codon 114 in the second EGF-like domain.