Novel aberrant splicings caused by a splice site mutation (IVS1a+5g>a) in F7 gene

Low FVII coagulant activity (FVII:C 8.2%) and antigen level (FVII:Ag 34.1%) in a 46-year-old Chinese male led to a diagnosis of coagulation factor VII (FVII) deficiency. Compound heterozygous mutations were identified in his F 7 gene:a G to A transition in the 5' donor splice site of intron 1a (IVS1a+5g>a) and a T to G transition at the nucleotide position 10961 in exon 8, resulting in a His to Gln substitution at amino acid residue 348. An analysis of ectopic transcripts of F7 in the leukocytes of the patient reveals that the mutation (IVS1a+5g>a) is associated with two novel aberrant patterns of splicing. The predominant alternative transcript removes exon 2, but retains intron 3, which shifts the reading frame and predicts a premature translation termination at the nucleotide positions 2-4 in intron 3. The minor alternative transcript skips both exon 2 and exon 3 (FVII Delta 2, 3), leading to an in-frame deletion of the propeptide and gamma-carboxylated glutamic acid (Gla) domains of mature FVII protein. In vitro expression studies of the alternative transcript FVII Delta 2,3 by transient transfection of HEK 293 cells with PcDNA 3.1(-) expression vector showed that although the mutant protein could be secreted, no pro-coagulation activity was detected. The coexistence of the two abnormal transcripts and a heterozygous mutation His348Gln, explained the patient's phenotype.