A Novel Mutation in the Fibrinogen Bβ Chain (c.490G>A; End of Exon 3) Causes a Splicing Abnormality and Ultimately Leads to Congenital Hypofibrinogenemia

Abstract

We found a novel heterozygous mutation in the fibrinogen Bβ chain (c.490G>A) of a 3-year-old girl with congenital hypofibrinogenemia. To clarify the complex genetic mechanism, we made a mini-gene including a FGB c.490G>A mutation region, transfected it into a Chinese Hamster Ovary (CHO) cell line, and analyzed reverse transcription (RT) products. The assembly process and secretion were examined using recombinant mutant fibrinogen. Direct sequencing demonstrated that the mutant RT product was 99 bp longer than the wild-type product, and an extra 99 bases were derived from intron 3. In recombinant expression, a mutant Bβ-chain was weakly detected in the transfected CHO cell line, and aberrant fibrinogen was secreted into culture media; however, an aberrant Bβ-chain was not detected in plasma. Since the aberrant Bβ-chain was catabolized faster in cells, the aberrant Bβ-chain in a small amount of secreted fibrinogen may catabolize in the bloodstream. FGB c.490G>A indicated the activation of a cryptic splice site causing the insertion of 99 bp in intron 3. This splicing abnormality led to the production of a Bβ-chain possessing 33 aberrant amino acids, including two Cys residues in the coiled-coil domain. Therefore, a splicing abnormality may cause impaired fibrinogen assembly and secretion.

Genetic Analysis of Afibrinogenemia and Hypofibrinogenemia: Novel Mutations in the <b><i>FGB</i></b> Gene in the Turkish Population

“…On the other hand, most patients with dysfibrinogenemia have heterozygous missense mutations leading to delayed or absent fibrinopeptide A release or defective fibrin polymerization causing a bleeding disorder or thrombophilia. It is important to characterize these mutations for the diagnosis, confirmation, or identification of potential carriers and a familial diagnosis [10]. A recent review of rare coagulation defects in Turkish patients revealed 15 fibrinogen deficiency patients [11].…”

Konjenital Hipofibrinojenemi veya Afibrinojenemi ? Yenidoğan Döneminde Tanısal Bir İkilem

“…However, new mutations are still reported. In two articles that were published in 2017, a new mutation in the FGB gene was defined in a case from China; and a total of 16 mutations were defined in 15 patients as 10 in the FGA gene; 3 in the FGB gene and 3 in the FGG gene were reported in a study from Pakistan 12 of which were new [16,17]. Defining these mutations, diagnosing and confirming the potential carriers, and characterizing them for a familial diagnosis are important.…”