Congenital afibrinogenemia: intracellular retention of fibrinogen due to a novel W437G mutation in the fibrinogen Bbeta-chain gene.
Congenital afibrinogenemia is a rare autosomal recessive coagulation disorder characterised by hemorrhagic manifestations of variable entity and by severe plasma fibrinogen deficiency. Among the 31 afibrinogenemia-causing mutations so far reported, only 2 are missense mutations and both are located in the fibrinogen Bbeta-chain gene. Direct sequencing of the fibrinogen gene cluster in two afibrinogenemic Iranian siblings revealed a novel homozygous T>G transversion in exon 8 (nucleotide position 8025) of the fibrinogen Bbeta-chain gene. The resulting W437G missense mutation involves a highly conserved amino acid residue, located in the C-terminal globular D domain. The role of the W437G amino acid substitution on fibrinogen synthesis, folding, and secretion was assessed by in vitro expression experiments in COS-1 cells, followed by qualitative and quantitative analyses of intracellular and secreted mutant fibrinogen. Results of both pulse-chase experiments and enzyme-linked immunosorbent assays demonstrated intracellular retention of the mutant W437G fibrinogen and marked reduction of its secretion. These data, besides elucidating the pathogenetic role of the W437G mutation in afibrinogenemia, underline the importance of the Bbeta-chain D domain in fibrinogen folding and secretion.
Spena
Silvia
S
Department of Biology and Genetics for Medical Sciences, University of Milan, Via Viotti, 3/5 -20133 Milan, Italy.
Asselta
Rosanna
R
Duga
Stefano
S
Malcovati
Massimo
M
Peyvandi
Flora
F
Mannucci
Pier Mannuccio
PM
Tenchini
Maria Luisa
ML
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D004797:Enzyme-Linked Immunosorbent Assay; D005340:Fibrinogen / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D010375:Pedigree; D017354:Point Mutation; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
C115499:BBeta fibrinogen; D005340:Fibrinogen