Afibrinogenemia: first identification of a splicing mutation in the fibrinogen gamma chain gene leading to a major gamma chain truncation

• Published in: Blood 2000-10, Vol.96 (7), p.2496-2500
• Main Authors: Asselta, Rosanna, Duga, Stefano, Simonic, Tatjana, Malcovati, Massimo, Santagostino, Elena, Giangrande, Paul L.F., Mannucci, Pier Mannuccio, Tenchini, Maria Luisa
• Format: Article
• Language: English
• Subjects: Afibrinogenemia - genetics; Amino Acid Sequence; Base Sequence; Biological and medical sciences; Child, Preschool; Consanguinity; Fibrinogen - chemistry; Fibrinogen - genetics; HeLa Cells; Hematologic and hematopoietic diseases; Hemorrhage - genetics; Humans; Male; Medical sciences; Molecular Sequence Data; Mutation; Pakistan; Pedigree; Platelet diseases and coagulopathies; Polymerase Chain Reaction; RNA Splicing; RNA, Messenger - biosynthesis; Sequence Analysis, DNA; Transfection
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V96.7.2496

Congenital afibrinogenemia is a rare autosomal recessive disorder characterized by the complete absence of plasma fibrinogen and by a bleeding tendency ranging from mild to moderately severe. Beside a deletion of the almost entire Aα-chain gene, only 2 missense mutations in the C-terminal domain of the Bβ-chain have been very recently described as being associated with afibrinogenemia. We studied a Pakistani patient with unmeasurable plasma levels of functional and immunoreactive fibrinogen. Sequencing of the fibrinogen genes revealed a homozygous G→A transition at position +5 of intron 1 of the γ-chain gene. The predicted mutant fibrinogen γ-chain would contain the signal peptide, followed by a short stretch of aberrant amino acids, preceding a premature stop codon. To demonstrate the causal role of the identified mutation, we prepared expression vectors containing a region of the fibrinogen γ-chain gene spanning from exon 1 to intron 4 and carrying either a G or an A at position +5 of intron 1. Transient transfection of the mutated plasmid in HeLa cells, followed by RNA extraction and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, allowed us to demonstrate the production of an erroneously spliced messenger RNA (mRNA), retaining intron 1, as shown by direct sequencing. A normal splicing occurred in HeLa cells transfected with the wild-type plasmid. This is the first report of a mutation in the fibrinogen γ-chain gene causing afibrinogenemia and indicates that, in addition to the Aα and Bβ-chain genes, the γ-chain gene must also be considered in mutation screening for afibrinogenemia.