Identification of Two Novel Fibrinogen Bβ Chain Mutations in Two Slovak Families with Quantitative Fibrinogen Disorders

Abstract

Congenital fibrinogen disorders are caused by mutations in one of the three fibrinogen genes that affect the synthesis, assembly, intracellular processing, stability or secretion of fibrinogen. Functional studies of mutant Bβ-chains revealed the importance of individual residues as well as three-dimensional structures for fibrinogen assembly and secretion. This study describes two novel homozygous fibrinogen Bβ chain mutations in two Slovak families with afibrinogenemia and hypofibrinogenemia. Peripheral blood samples were collected from all subjects with the aim of identifying the causative mutation. Coagulation-related tests and rotational thromboelastometry were performed. All exons and exon–intron boundaries of the fibrinogen genes (FGA, FGB and FGG) were amplified by PCR followed by direct sequencing. Sequence analysis of the three fibrinogen genes allowed us to identify two novel homozygous mutations in the FGB gene. A novel Bβ chain truncation (BβGln180Stop) was detected in a 28-year-old afibrinogenemic man with bleeding episodes including repeated haemorrhaging into muscles, joints, and soft tissues, and mucocutaneous bleeding and a novel Bβ missense mutation (BβTyr368His) was found in a 62-year-old hypofibrinogenemic man with recurrent deep and superficial venous thromboses of the lower extremities. The novel missense mutation was confirmed by molecular modelling. Both studying the molecular anomalies and the modelling of fibrinogenic mutants help us to understand the extremely complex machinery of fibrinogen biosynthesis and finally better assess its correlation with the patient’s clinical course.

Human Fibrinogen: Molecular and Genetic Aspects of Congenital Disorders

“…At the end of 2017, novel nonsense variants in afibrinogenemic patients have been reported. In a 28-year-old afibrinogenemic man presenting with mucocutaneous bleeding and blood losses into muscles, joints, and soft tissues, the Gln180Stop “Martin” variant was identified in FGB [ 43 , 44 ]. Naz and colleagues described the novel FGA p.Gln183stop and FGG p.Lys121stop nonsense variants in two afibrinogenemic patients from Pakistan [ 45 ].…”

“…In a non-thrombophilic woman, who experienced thrombosis events and miscarriages, Casini and colleagues identified the fibrinogen beta chain p.Gly472Val missense change [ 51 ]. Furthermore, in a 62-year-old hypofibrinogenemic man with a history of venous thromboses, the fibrinogen beta chain p.Tyr368His variant was found [ 43 ]. Protein modeling represents a helpful tool to understand functionality and causality of genetic variants identified in fibrinogen beta chain [ 52 ].…”

Genetic Variants in the FGB and FGG Genes Mapping in the Beta and Gamma Nodules of the Fibrinogen Molecule in Congenital Quantitative Fibrinogen Disorders Associated with a Thrombotic Phenotype

“…The pathogenesis at the basis of the paradoxical thrombotic tendency in congenital quantitative fibrinogen disorders is likely multifactorial, depending on exogenous and endogenous risk factors such as genetic thrombophilia, use of fibrinogen concentrate, trauma, immobilization, or pregnancy. The true mechanisms of thrombosis in these patients still remain unexplained [26,45].…”

Women With Congenital Hypofibrinogenemia/Afibrinogenemia: From Birth to Death

“…3 Paradoxically, thrombosis in both venous and arterial sites are also a typical complication of congenital FIB disorders, in addition to bleeding symptoms. 4,5 In their study, the authors identified 2 novel FIB mutations in 2 Slovak families with quantitative FIB disorders and concluded the development of thrombotic complications was spontaneous since the patient and his son did not receive substitution therapy with the FIB concentrate in the period of their recurrent thromboses manifestation. 5 Due to their specific physiological characteristics, female patients tend to have congenital hypofibrinogenemia/afibrinogenemia, such as spontaneous recurrent abortion, menorrhagia, infertility, antepartum and postpartum hemorrhage, and so on.…”

“…4,5 In their study, the authors identified 2 novel FIB mutations in 2 Slovak families with quantitative FIB disorders and concluded the development of thrombotic complications was spontaneous since the patient and his son did not receive substitution therapy with the FIB concentrate in the period of their recurrent thromboses manifestation. 5 Due to their specific physiological characteristics, female patients tend to have congenital hypofibrinogenemia/afibrinogenemia, such as spontaneous recurrent abortion, menorrhagia, infertility, antepartum and postpartum hemorrhage, and so on. 6,7 Current studies of congenital hypofibrinogenemia/afibrinogenemia mainly focus on different types of FIB mutations, etiology/pathogenesis, some rare case reports of the diseases, and the relationship of hotspot FIB gene mutations associated with recurrent deep vein thromboses as serious manifestation of thrombotic phenotype.…”