A novel γ-chain Tyr306Asn missense mutation causes congenital dysfibrinogenemia.

Background

Congenital dysfibrinogenemia is an inherited disorder caused by fibrinogen gene defects, leading to structural and functional abnormalities of the protein. We identified a novel heterozygous γTyr306Asn mutation in a 26-year-old woman and aimed to elucidate its pathogenic mechanism.

Method

The study used coagulation assays, genetic analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, liquid chromatography-tandem mass spectrometry, fibrin polymerization, fibrin clot dissolution, cross-linking, sequence conservation analysis, bioinformatics analysis, and molecular modeling.

Results

The proband's fibrinogen levels were 1.66 g/L by the Clauss assay and 5.38 g/L by the PT-derived method. Sequencing identified a novel heterozygous γTyr306Asn mutation in the fibrinogen gene. Mass spectrometry detected both normal and mutant fibrinogen peptides in patient plasma. Amino acid sequence alignment revealed that γTyr306 is highly conserved across homologous species. Furthermore, multiple online bioinformatics tools consistently predicted that this mutation would significantly impair protein structure or function. Molecular modeling analysis revealed that the γTyr306Asn mutation alters the spatial conformation and electrostatic interactions of the amino acid, resulting in structural distortion of the local β-sheet. This perturbation was predicted to alter the local β-sheet conformation and may interfere with D:D-mediated fibrin assembly. Fibrin polymerization confirmed that the proband's fibrinogen had a decreased aggregation rate and defective fibrin aggregation. Clot lysis and cross-linking remained unaffected.

Conclusions

The novel γTyr306Asn variant was associated with impaired fibrin polymerization. The combined structural and functional findings support a pathogenic mechanism involving disturbed D:D-mediated fibrin assembly.