Synonymous variant at the terminal nucleotide in exon 3 of F7 causes abnormal splicing: A case report.

Background: Synonymous variants are non-pathogenic due to non-substitution of amino acids. However, synonymous exonic terminal nucleotide substitutions may affect splicing. Splicing variants are easily analyzed at RNA level for genes expressed in blood cells. Minigene analysis provides another method for splicing variant analysis of genes that are poorly or not expressed in peripheral blood.

Methods: Whole exome sequencing was performed to screen for potential pathogenic mutations in the proband, which were validated within the family by Sanger sequencing. The pathogenicity of the synonymous mutation was analyzed using the minigene technology.

Results: The proband harbored the compound heterogeneous variants c. [291G >A; 572-50C >T] and c.681 + 1G >T in F7, of which the synonymous variant c.291G >A was located at the terminal position of exon 3. Minigene analysis revealed exon3 skipping due to this mutation, which may have subsequently affected protein sequence, structure, and function.

Conclusion: Our finding confirmed the pathogenicity of c.291G >A, thus extending the pathogenic mutation spectrum of F7, and providing insights for effective reproductive counseling.