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

Tomas Simurda,Jana Zolkova,Juraj Sokol,Peter Kubisz,Zora Lasabova,Ingrid Skornova,Zuzana Snahnicanova,Dusan Loderer,Jan Stasko,Jan Hudecek

doi:10.3390/ijms19010100

Tomas Simurda, Jana Zolkova + Show 8 more

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https://doi.org/10.3390/ijms19010100

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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.

Highlights

Fibrinogen is a 340 kDa glycoprotein comprising pairs of three polypeptide chains termed Aα, Bβ and γ that are linked by an extensive network of 29 intra- and inter-chain disulphide bridging and represented as (Aα-Bβ-γ)2 [1,2]
The fibrinogen molecule consists of two sets of three polypeptide chains (Aα, Bβ, and γ) that are joined in their amino-terminal regions by disulphide bridges to form the E region
The outer D regions contain the globular C terminal domains of the Bβ chain and γ chain.Unlike the βC and γC domains, the C-terminal domains of the Aα chain are intrinsically unfolded and flexible and tend to be noncovalently tethered in the vicinity of the central E region [4]. These domains contain constitutive binding sites that participate in fibrinogen conversion to fibrin, fibrin assembly, crosslinking, and platelet interactions, as well as sites that are available after fibrinopeptide cleavage

Summary

Introduction

Fibrinogen is a 340 kDa glycoprotein comprising pairs of three polypeptide chains termed Aα, Bβ and γ that are linked by an extensive network of 29 intra- and inter-chain disulphide bridging and represented as (Aα-Bβ-γ)2 [1,2]. The outer D regions contain the globular C terminal domains of the Bβ chain (βC) and γ chain (γC).Unlike the βC and γC domains, the C-terminal domains of the Aα chain (αC) are intrinsically unfolded and flexible and tend to be noncovalently tethered in the vicinity of the central E region [4]. These domains contain constitutive binding sites that participate in fibrinogen conversion to fibrin, fibrin assembly, crosslinking, and platelet interactions, as well as sites that are available after fibrinopeptide cleavage. Proteolysis of fibrinogen by thrombin enables polymerization to form fibrin clots [5]

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