PubMed · 1784907
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B Boneu. 1991-10-01. [Prolonged bleeding time. Diagnostic orientation].. https://pubmed.ncbi.nlm.nih.gov/1784907/
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Congenital afibrinogenemia/hypofibrinogenemia is an extremely rare coagulation disorder. We describe a case of congenital hypofibrinogenemia in a 6-year female child, who presented with recurrent ecchymotic spots with no frank bleeding.
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.
Staphylococcus aureus undergoes a density-dependent conversion in phenotype from tissue-adhering to tissue-damaging and phagocyte-evading that is mediated in part by the quorum-sensing operon, agr, and its effector, RNAIII. Contributions of host factors to this mechanism for regulating virulence have not been studied. We hypothesized that fibrinogen, as a component of the inflammatory response, could create spatially constrained microenvironments around bacteria that increase density independently of bacterial numbers and thus potentiate quorum-sensing-dependent virulence gene expression. Here we show that transient fibrinogen depletion significantly reduces the bacterial burden and the consequential morbidity and mortality during experimental infection with wild-type S. aureus, but not with bacteria that lack expression of the quorum-sensing operon, agr. In addition, it inhibits in vivo activation of the promoter for the agr effector, RNAIII, and downstream targets of RNAIII, including alpha hemolysin and capsule production. Moreover, both in vitro and in vivo, the mechanism for promoting this phenotypic switch in virulence involves clumping of the bacteria, demonstrating that S. aureus responds to fibrinogen-mediated bacterial clumping by enhancing density-dependent virulence gene expression. These data demonstrate that down-modulation of specific inflammatory components of the host that augment bacterial quorum sensing can be a strategy for enhancing host defense against infection.