Novel management of anticoagulant resistant thrombotic hypodysfibrinogenaemia

How I treat dysfibrinogenemia

Congenital dysfibrinogenemia (CD) is caused by structural changes in fibrinogen that modify its function. Diagnosis is based on discrepancy between decreased fibrinogen activity and normal fibrinogen antigen levels and is confirmed by genetic testing. CD results from monoallelic mutations in fibrinogen genes leading to clinically heterogenous disorders. Most patients with CD are asymptomatic at time of diagnosis but the clinical course may be complicated by a tendency to bleeding and/or thrombosis. Patients with a thrombotic-related fibrinogen variant are particularly at risk and in such patients long-term anticoagulation should be considered. Management of surgery and pregnancy raise important and difficult issues. The mainstay of CD treatment remains fibrinogen supplementation. Antifibrinolytic agents are part of the treatment in some specific clinical settings. In this article, we discuss five clinical scenarios to highlight common clinical challenges. We detail our approach to establish a diagnosis of CD and discuss strategies for the management of bleeding, thrombosis, surgery and pregnancy.

Fibrin clot properties to assess the bleeding phenotype in unrelated patients with hypodysfibrinogenemia due to novel fibrinogen mutations

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 cm² in P1, and 20 ± 0.1 × 10^-9 cm² in P2 and P3, compared to 6 ± 2 × 10^-9 cm² 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.

Genetics, diagnosis and clinical features of congenital hypodysfibrinogenemia: a systematic literature review and report of a novel mutation

Essentials Hypodysfibrinogenemia is rarely reported among the congenital fibrinogen disorders. This first systematic literature review led to identification of 51 hypodysfibrinogenemic cases. Diagnosis based only on functional/antigenic fibrinogen ratio may be insufficient. Family studies show an incomplete segregation of mutation with the clinical phenotypes.

SUMMARY

Background Hypodysfibrinogenemia is a rare disease characterized by decreased levels of a dysfunctional fibrinogen. It shares features with both hypo- and dysfibrinogenemia, although with specific molecular patterns and clinical phenotypes. Objectives To better define the genetics, the diagnosis and the clinical features of hypodysfibrinogenemia. Patients/Methods A systematic literature search led to 167 records. After removal of duplicates, abstract screening and full-text reviewing, 56 molecular and/or clinical studies were analyzed, including a novel FGB missense mutation in a woman with a mild bleeding phenotype. Results A total of 32 single causative mutations were reported, mainly in the COOH-terminal region of the γ or Aα chains at heterozygous or homozygous state. Seven additional hypodysfibrinogenemias were due to compound heterozygosity. The hypofibrinogenemic phenotypes were a result of an impaired assembly or secretion or an increased clearance of the fibrinogen variant, whereas the dysfibrinogenemic phenotype was mainly a result of a defective fibrin polymerization and an abnormal calcium or tPA binding. Among 51 identified index cases, a functional/antigenic fibrinogen ratio < 0.7 had a sensitivity of 86% for the diagnosis of hypodysfibrinogenemia. Eleven patients (22%) were asymptomatic at time of diagnosis, 23 (45%) had a mild bleeding phenotype with mainly obstetrical or gynecologic-related hemorrhage and 22 (43%) had experienced at least one thrombotic event, including 23 venous and eight arterial thromboses. Conclusions This first systematic review on hypodysfibrinogenemia shows the heterogeneity of causative mutations and that misdiagnosis could occur in relation to the functional and antigenic fibrinogen levels. Family studies reveal an incomplete segregation of the mutation with the clinical phenotype.

Thrombosis in Inherited Fibrinogen Disorders

Although inherited fibrinogen disorders (IFD) are primarily considered to be bleeding disorders, they are associated with a higher thrombotic complication risk than defects in other clotting factors. Managing IFD patients with thrombosis is challenging as anticoagulant treatment may exacerbate the underlying bleeding risk which can be life-threatening. Due to the low prevalence of IFD, there is little information on pathophysiology or optimal treatment of thrombosis in these patients. We searched the literature for cases of thrombosis among IFD patients and identified a total of 128 patient reports. In approximately half of the cases, thromboses were spontaneous, while in the others trauma, surgery, and parturition contributed to the risk. The true mechanism(s) of thrombosis in IFD patients remain to be elucidated. A variety of anticoagulant treatments have been used in the treatment or prevention of thrombosis, sometimes with concurrent fibrinogen replacement therapy. There is no definite evidence that fibrinogen supplementation increases the risk of thrombosis, and it may potentially be effective in the treatment and prevention of both thrombosis and hemorrhage in IFD patients.