Mutations in the gap junction protein beta-2 gene (‘GJB2’) are known to be responsible for mild to profound congenital and late-onset hearing loss. This study aimed to investigate the molecular basis of progressive hearing loss compared with non-progressive hearing loss.

Following clinical otorhinolaryngological evaluation, a genetic analysis was performed in a cohort of 72 patients with progressive sensorineural hearing loss.

Pathological genotypes were established in 16 patients (22.2 per cent). Six different gap junction protein beta-2 gene mutations were detected in 15 patients, with the c.35delG mutation responsible for 56 per cent of the mutated alleles. A novel gap junction protein beta-6 gene (‘GJB6’) mutation (p.Met203Val) was observed in one patient with mild progressive hearing loss.

Analyses of gap junction protein beta-2 and -6 genes revealed that similar pathological genotypes, occurring with similar frequencies, were responsible for progressive hearing loss, compared with reported genotypes for non-progressive hearing loss patients. Thus, genotype cannot be used to differentiate non-progressive from progressive hearing loss cases; in this study, patients both with and without an established pathological genotype had a similar clinical course.

To investigate the prevalence of mutations in the coding exon of the GJB2 gene in Iranian children with cochlear implants, and to compare the outcomes of auditory perception and speech production in cochlear-implanted children with and without GJB2 mutation.

One hundred and sixty-six prelingually deaf children who had undergone cochlear implantation at the Iranian Cochlear Implant Center, Tehran, were selected from a pool of 428 implanted children. The prevalence of GJB2 gene mutations was assessed using nested polymerase chain reaction and direct sequencing. To enable comparisons, we also identified 36 implanted children with non-GJB2 deafness. Patients' speech perception and speech production were assessed using the Categorization of Auditory Performance and Speech Intelligibility Rating scales.

Thirty-three of 166 probands (19.9 per cent) were found to have GJB2 deafness-causing allele variants and were diagnosed with DFNB1 deafness. Results also indicated a significant improvement in speech perception and production scores in both GJB2 and non-GJB2 patients over time.

Children with GJB2-related deafness benefit from cochlear implantation to the same extent as those with non-GJB2-related deafness.