Exonic mutations and exon skipping: Lessons learned from DFNA5.

Area of Science:

• Genetics
• Molecular Biology
• Otolaryngology

Background:

• Splicing dysregulation is implicated in inherited diseases, including deafness.
• Mutations in the DFNA5 gene can cause deafness through altered splicing of exon 8, leading to a truncated protein.
• Previously, only intronic mutations affecting DFNA5 exon 8 splicing were known.

Purpose of the Study:

• To identify novel mutations in the DFNA5 gene associated with postlingual progressive autosomal dominant non-syndromic hearing loss.
• To investigate the role of exonic mutations in DFNA5-related deafness.
• To expand the known spectrum of DFNA5 mutations causing hearing impairment.

Main Methods:

• Utilized next-generation sequencing (OtoSCOPE and whole exome sequencing) in five families with hearing loss.
• Employed a bioinformatics pipeline for variant filtering based on allele frequency and functional impact.
• Validated the functional consequences of identified mutations using in vitro mini-gene splicing assays.

Main Results:

• Identified three novel and two recurrent mutations in the DFNA5 gene that segregate with hearing loss.
• The novel mutations are missense variants located within exon 8.
• Computational predictions and in vitro assays confirmed that these exonic mutations decrease or abolish DFNA5 splicing efficiency.

Conclusions:

• This study reports the first exonic mutations in DFNA5 identified as a cause of inherited deafness.
• The findings broaden the mutational spectrum for DFNA5-related hearing loss.
• Emphasizes the critical need to evaluate the impact of coding variants on gene splicing in the context of inherited diseases.