Case Report: Laboratory detection of a thrombotic tendency in a family with hypodysfibrinogenemia and a novel FGG mutation

Abstract

Introduction: Hypodysfibrinogenemia is a rare congenital fibrinogen disorder (CFD) which may induce thrombotic and bleeding events. Therefore, patient management needs careful evaluation. Routine coagulation tests are inadequate to predict the clinical phenotype.

Clinical findings: A 60-year-old woman with both bleeding and thrombotic complications and her two daughters were referred to our center for genotypic and phenotypic analysis of a CFD.

Diagnosis: Conventional laboratory results led to the diagnosis of hypodysfibrinogenemia in all three subjects. They all carried the same heterozygous c.1124A>G mutation in FGG resulting in p.Tyr375Cys amino acid substitution, which was confirmed by protein variant analysis from plasma. In silico structure analysis predicted possible conformational and functional changes of the fibrinogen molecule. Thrombin generation indicated a hypercoagulable state confirmed by microfluidics that showed enhanced fibrin formation in both daughters, regardless of the coagulation trigger.

Conclusion: We report on a family with hypodysfibrinogenemia and a novel FGG heterozygous missense mutation, possibly leading to conformational changes or covalent dimerization. Thrombin generation and particularly microfluidic measurements disclosed a hypercoagulable state, which was not detected with routine coagulation tests, justifying a different patient management.

Keywords: case report; congenital fibrinogen disorders; diagnosis; hypodysfibrinogenemia; phenotype.

Figure 1

Timeline of the episodes of care of the proband.

Figure 2

Confirmation of p.Tyr375Cys amino acid substitution by mass spectrometry analysis of fibrinogen γ chain from plasma. Peptides unique to wild-type (A,B) or variant (C,D) fibrinogen γ chain were quantified in plasma. LC chromatogram and mass spectra shown with product fragments unique to the variant sequence indicated by asterisk. (E) Tryptic peptide representing wild-type fibrinogen γ chain in pooled normal plasma (control) and plasma of studied family members. (F) Tryptic peptide representing variant p.Tyr375Cys measured in pooled normal plasma (control) and plasma of studied family members.

Figure 3

Fluorescence microscopic images from the microfluidic assay showing fibrin deposition, imaged at t = 10 min. Alexa Fluor-647 fibrinogen was added to whole blood to visualize fibrin formation. Citrate blood samples were recalcified with CaCl₂/MgCl₂ and perfused over collagen III or collagen I ± tissue factor (TF), at a shear rate of 1,000 s⁻¹. Data obtained from daughters 1 and 2 were compared to 6 healthy donors (1 representative control is shown). Scale bar = 40 µm.