Compound heterozygosity for dominant and recessive GJB2 mutations in a Tunisian family and association with successful cochlear implant outcome

Abstract

Objectives: Mutations of GJB2 encoding connexin 26 are the most common cause of hearing loss. They are responsible for up to 50% of ARNSHL. The pathogenic mutations in this gene are generally inherited recessively. Dominant mutations in GJB2 also cause hearing loss, either in isolated non-syndromic form or as part of a syndrome associated with various skin disorders.

Methods: We screened a Tunisian child affected by congenital, bilateral, profound, sensorineural hearing loss for mutations in GJB2 gene using PCR and direct sequencing.

Results: The proband was found to be compound heterozygous for recessive and dominant GJB2 mutations respectively p.V37I (c.109G > A) and p.R143Q (c.428G > A). Surprisingly the hearing mother is a carrier for this dominant GJB2 mutation. This proband underwent a cochlear implant at four years old. The evaluation using APCEI and IT-MAIS tests at six months post implantation indicates a successful cochlear implant outcome since the deaf child began to acquire language abilities and auditory sensation.

Conclusions: The p.R143Q mutation was described for the first time in Tunisia. We confirm the low penetrance of this mutation since the proband mother is a carrier despite her normal hearing. We show the effectiveness of cochlear implant to restore the communication abilities and auditory sensation for our patient.

Keywords: Cochlear implant; Dominant; GJB2; Hearing loss; Penetrance; Tunisia.