Activation of multiple cryptic donor splice sites by the common congenital afibrinogenemia mutation, FGA IVS4+1 G→T

Our recent studies on the molecular basis of the autosomal recessive disorder congenital afibrinogenemia showed that the most common mutation is a donor splice mutation in FGA intron 4, IVS4 + 1 G-->T, accounting for approximately half of disease alleles, The effect of this mutation on messenger RNA (mRNA) splicing, however, remained unproven. COS-7 cells transfected with a normal plasmid construct produced 100% mRNA molecules with correct splicing, whereas cells transfected with a mutant construct produced multiple aberrant mRNAs, due to utilization of cryptic donor splice sites situated in exon 4 and intron 4, One particular site situated 4 base pairs (bp) downstream of the normal site was used in 85% of transcripts causing afibrinogenemia by a 4-bp insertion-frameshift, leading to ipremature alpha-chain truncation. Our results confirm the utility of transfecting COS-7 cells to study mRNA splice-site mutations and demonstrate that the common FGA IVS4 variant is a null mutation leading to afibrinogenemia, (Blood, 2001;97: 1879-1881) (C) 2001 by The American Society of Hematology.