Factor VII verona coagulation disorder: double heterozygosis with an abnormal factor VII and heterozygous factor VII deficiency.
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This report describes the findings of a genetic analysis of the factor VII (FVII) gene in a Japanese, male patient with FVII deficiency. The proband showed FVII activity level of 25% and FVII antigen level of 28% of the normal value, but he had no severe bleeding episodes. We identified the mutation by direct sequencing of polymerase chain reaction products representing all exons except 1b and their flanking intronic regions of his FVII gene. We detected a single point mutation, a C-->T substitution at nucleotide position 7863 in exon 5, which results in an amino acid replacement of Arg (CGC) to Cys (TGC) at codon 110 in the second epidermal growth factor-like domain. Homozygosity was confirmed in the propositus by loss of a site for the restriction endonuclease Eco47III. Furthermore, his parents, who had moderately reduced levels of factor VII activity and antigen, carried this mutation site as a heterozygote. Although the Arg11O residue is located distal to the tissue factor (TF) in the soluble TF-FVIIa crystal structure, we infer that the replacement of the positively charged and larger Arg residue with a neutral Cys residue may be likely to impair proper folding, resulting in destabilization of the protein structure.
We investigated a Sephardic Jewish patient with a mild bleeding diathesis whose plasma levels of factor VII coagulant activity and factor VII antigen were 7% and 9% of normal, respectively. Sequencing demonstrated homozygosity for the Ala244Val mutation and the Arg353Gln polymorphism, which is associated with a modest decrease in factor VII levels. To elucidate the mechanism by which Ala244Val reduced factor VII levels in this patient, transient transfections were performed in COS-1 cells with wild type and mutant factor VII cDNAs and factor VII antigen levels in cell lysates and conditioned media were measured. The secretion of the mutant protein (FVII244V) into the media was 20% of wild type (FVIIwt), and intracellular levels of FVII244V were 60% of FVIIwt. A construct encoding Ala244Val along with the Arg353Gln polymorphism decreased the factor VII level in the media to that observed in the patient's plasma. Pulse-chase experiments demonstrated that FVII244V did not accumulate intracellularly and that low levels of the abnormal protein were maintained throughout the chase. To test the hypothesis that FVII244V results in an unstable molecule, amino acids with smaller (Gly) or larger (Phe) side chains were substituted for Val244 by site-directed mutagenesis. Transient transfection assays with these constructs demonstrated that the side chain of amino acid 244 is crucial in maintaining a proper conformation of the molecule. We conclude that Ala244Val results in a factor VII molecule that is unstable and is probably degraded intracellularly.
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