Two missense mutations in SLC26A4 gene: a molecular and functional study

Area of Science:

• Genetics
• Molecular Biology
• Otolaryngology

Background:

• Mutations in the SLC26A4 gene are linked to non-syndromic hearing loss (DFNB4) and Pendred syndrome (PS).
• Pendred syndrome is characterized by congenital hearing loss and thyroid dysfunction.
• SLC26A4 encodes pendrin, an essential anion transporter.

Purpose of the Study:

• Investigate the genetic basis of profound hearing loss in eight Tunisian families.
• Identify specific SLC26A4 mutations responsible for hearing loss.
• Elucidate the molecular mechanisms underlying the identified mutations' pathogenicity.

Main Methods:

• Microsatellite marker genotyping to establish linkage to SLC26A4.
• DNA sequencing and PCR-RFLP to identify missense mutations.
• Transient expression of wild-type and mutant SLC26A4 in cell lines (COS7, 8305C).
• Analysis of pendrin protein expression, glycosylation, and cellular localization using RT-PCR, Western blot, and immunofluorescence.

Main Results:

• Identified two missense mutations, p.L445W and p.M147T, in SLC26A4 in affected families.
• The p.L445W mutation showed a founder effect in seven of the eight families.
• Both mutations were demonstrated to abolish complex glycosylation of pendrin.
• Mutant pendrin failed to be targeted to the plasma membrane in cellular expression studies.

Conclusions:

• The identified SLC26A4 mutations, p.L445W and p.M147T, are pathogenic causes of profound hearing loss in the studied Tunisian population.
• These mutations disrupt pendrin's glycosylation and plasma membrane localization, leading to functional impairment.
• Understanding these molecular mechanisms provides insight into the pathogenesis of hearing loss and Pendred syndrome.