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

Mutations in the SLC26A4 gene encoding pendrin, an anion transporter, are responsible for non-syndromic hearing loss (HL) (DFNB4) and Pendred syndrome (PS). PS is a genetic disorder that causes early HL and affects the thyroid gland. Here, we report eight Tunisian families affected with profound HL. Clinical investigations revealed goiter in few patients. Genotyping using microsatellite makers showed linkage to SLC26A4, and missense mutations p. L445W and p. M147T were identified by sequencing and polymerase chain reaction-restriction fragment length polymorphism. The p. L445W mutation segregated in seven families and haplotype analysis suggested its founder effect. In order to understand the molecular pathogenic mechanisms of p. L445W and p. M147T mutations, SLC26A4 wild-type and mutant cDNA constructs were transiently expressed in COS7 cells and several human cell lines including Thyroid 8305C cells. Reverse transcription-PCR, western blot and immunofluorescence demonstrated that these two mutations abolished complex glycosylation of pendrin and prevented its targeting to the plasma membrane.