Fibrin clot properties to assess the bleeding phenotype in unrelated patients with hypodysfibrinogenemia due to novel fibrinogen mutations
Rita Marchi, R. Vilar, Stéphane Durual, Matthew Goodyer, Valérie Gay, Marguerite Neerman‐Arbez, Alessandro Casini
Abstract
Congenital hypodysfibrinogenemia is a rare fibrinogen disorder, defined by decreased levels of a dysfunctional fibrinogen. We present the functional and structural characterization of two new fibrinogen variants. A duplication of 32 bases in FGA exon 5, p.Ser382GlyfsTer50 was identified in a patient (P1) with history of hemoptysis and traumatic cerebral bleeding. A missense mutation in FGG exon 8, p.Ala353Ser was identified in two siblings (P2 and P3) with tendency to bruising and menorrhagia. Fibrin polymerization was studied in plasma and in purified fibrinogen by turbidimetry. Fibrin structure was studied by a permeability assay, laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). In both plasma and purified fibrinogen samples, all patients had an abnormal polymerization characterized by a decreased maximal absorption compared to controls. The permeation constant (Ks) was markedly increased in all patients: 31 9 10 -9 cm 2 in P1, and 20 0.1 10 -9 cm 2 in P2 and P3, compared to 6 2 10 -9 cm 2 in the control (p < 0.05). The presence of very large pores that accounts for the increased Ks was confirmed by LSCM and SEM patients' clots images. By SEM, the patients' fibrin fibers diameters were thicker: 90 25 nm in P1, 162 64 nm in P2 and 132 46 nm in P3 compared to 74 25 nm in control (p < 0.0001). In conclusion, both new causative fibrinogen mutations altered clot structure by forming thick fibers, diminishing fiber branching, and increasing pore filling space. These structural changes to clots explain the patients' bleeding phenotypes.