title: Missense or splicing mutation? The case of a fibrinogen Bbeta-chain mutation causing severe hypofibrinogenemia.
abstract: The genetic basis of severe hypofibrinogenemia was analyzed in a 57-year-old Italian woman. She turned out to be a compound heterozygote for a novel putative missense mutation (Leu172Gln) and a previously described nonsense mutation (Arg17Stop) in the fibrinogen Bbeta-chain gene. The pathogenetic role of Leu172Gln was analyzed by in vitro expression of the mutant recombinant protein in COS-1 cells. These experiments demonstrated that mutant Bbeta-Leu172Gln fibrinogen was normally assembled and secreted. Inspection of the nucleotide sequence surrounding the mutation suggested a possible role on pre-messenger RNA (mRNA) splicing. Production of the mutant transcript in HeLa cells confirmed that the mutation activates a cryptic acceptor splice site in exon 4, resulting in a truncated Bbeta chain, lacking approximately 70% of the C-terminal region. This represents the first exonic splicing mutation identified in the fibrinogen genes. These findings strengthen the importance to analyze potentially pathogenetic nucleotide variations at both the protein and the mRNA level.
authors.affiliation: Department of Biology and Genetics for Medical Sciences, University of Milan, Milan, Italy.
authors.forename: Rosanna
authors.initials: R
authors.lastname: Asselta
authors.forename: Stefano
authors.initials: S
authors.lastname: Duga
authors.forename: Silvia
authors.initials: S
authors.lastname: Spena
authors.forename: Flora
authors.initials: F
authors.lastname: Peyvandi
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Castaman
authors.forename: Massimo
authors.initials: M
authors.lastname: Malcovati
authors.forename: Pier Mannuccio
authors.initials: PM
authors.lastname: Mannucci
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Tenchini
mesh_terms: D000347:Afibrinogenemia / Q000097:blood* / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D018389:Codon, Nonsense; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D005340:Fibrinogen / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D006579:Heterozygote; D006801:Humans; D008875:Middle Aged; D020125:Mutation, Missense; D012326:RNA Splicing / Q000235:genetics*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: C115499:BBeta fibrinogen; D018389:Codon, Nonsense; D018076:DNA, Complementary; D011994:Recombinant Proteins; D005340:Fibrinogen