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Mutations in GJB2 encoding Connexin 26 (CX26) are associated with hearing loss and hyperproliferative skin disorders of differing severity including keratitis‐ichthyosis‐deafness (KID) and Vohwinkel syndrome. A 6‐year‐old Caucasian girl who presented with recurrent skin rashes and sensorineural hearing loss harboured a heterozygous point mutation in GJB2 (c.424T > C; p.F142L). To characterize the impact of CX26F142L on cellular events. Plasmids CX26WT, CX26F142L, CX26G12R (KID) or CX26D66H (Vohwinkel) were transfected into HeLa cells expressing Cx26 or Cx43 or into HaCaT cells, a model keratinocyte cell line. Confocal microscopy determined protein localization. MTT assays assessed cell viability in the presence or absence of carbenoxolone, a connexin‐channel blocker. Co‐immunoprecipitation/Western blot analysis determined Cx43:Cx26 interactions. Quantitative real‐time polymerase chain reaction assessed changes in gene expression of ER stress markers. Dye uptake assays determined Connexin‐channel functionality. F142L and G12R were restricted to perinuclear areas. Collapse of the microtubule network, rescued by co‐treatment with paclitaxel, occurred. ER stress was not involved. Cell viability was reduced in cells expressing F142L and G12R but not D66H. Unlike G12R that forms "leaky" hemichannels, F142L had restricted permeability. Cell viability of F142L and G12R transfected cells was greater in HeLa cells expressing Cx43 than in native Cx‐free HeLa cells. Co‐immunoprecipitation suggested a possible interaction between Cx43 and the three mutations. Expression of CX26F142L and G12R results in microtubule collapse, rescued by interaction with Cx43. The GJB2 mutations interacted with Cx43 suggesting that unique Cx43:Cx26 channels are central to the diverse phenotype of CX26 skin‐related channelopathies. [ABSTRACT FROM AUTHOR]

Mutations in the Gjb2 gene, which encodes a gap junction protein connexin26 (Cx26), are the most prevalent form of hereditary deafness in humans and represent about half of non-syndromic congenital deafness cases in many ethnic populations. Cochlear potassium (K+) recycling in mature cochlea is required for normal hearing. It is thought that gap junctions are essential for K+ recycling and that Gjb2 mutations cause Gjb2-associated deafness by disrupting K+ recycling in mature cochlea. Here we present evidence showing that Gjb2 is required for normal development of the neonatal organ of Corti prior to the onset of the hearing in mice. In the conditional Gjb2 null (cCx26 null) mice, ribbon synapses in inner hair cells remained poorly developed, the afferent type I fibers failed to finish the refinement process to form convergent innervation to individual inner hair cells. The spontaneous depolarizing activities in the supporting cells, which normally diminish in the wild type cochleae after postnatal day 8 (P8), remained strong in the cochlea after P8 in the mutant mice. Furthermore, the deafness phenotype was readily generated only if the Cx26 expression in the organ of Corti was significantly reduced before P6. Similar amount of Cx26 reduction in more mature cochleae had a much weaker effect in damaging the hearing sensitivity. Our findings indicated that Cx26 plays essential roles in the maturation process of the organ of Corti prior to the establishment of high K+ in the endolymph and the onset of hearing. These results suggest that successful treatment of Cx26 deafness requires early intervention before the cochlea fully matures.

Introduction: Audiological performance in cochlear implanted children may vary depending of the etiology of the deafness, one of which is GJB2 gene mutations. Aim: In this study we evaluated the auditory performance by pure tone audiogram testing after unilateral cochlear implantation for children with GJB2 related mutations and to compare the results with the ones from children that did not show any mutations in the GJB2 gene. Material and Methods: We have determined the auditory tonal thresholds in 28 patients and we calculated the average of these thresholds for the frequencies of 500, 1000, 2000 and 4000Hz. We have taken into consideration the first tonal thresholds that averaged at 35dB or better for the given frequencies. Results and Discussions: Comparison between the average tonal thresholds between the two groups show that even though children from the GJB2 mutation related deafness group need a slightly longer period of time to reach minimal conversational level thresholds, the dB value of these levels is lower than the ones in the second group. Conclusions: This can prove to be a useful tool for the clinician regarding cochlear implant counselling and for the patient in terms of better speech understanding skills and oral communication with parents and educational staff.

Conclusions: Outcomes following cochlear implantation in children with congenital cytomegalovirus (CMV) infection were almost equivalent to those of children with GJB2 mutation-related sensorineural hearing loss (SNHL). Although our patients with developmental disorder showed poor auditory performance and speech and language skills after cochlear implantation, SNHL with developmental disorder should not be a contraindication for the procedure. Objective: Congenital CMV infection accounts for approximately 20% of all cases of neonatal hearing loss, while the GJB2 mutation accounts for 30-50% of all cases of profound nonsyndromic hearing loss. Here, outcomes for auditory behavior and speech and language skills were compared in children with congenital CMV infection or GJB2 mutation who received cochlear implantation for profound SNHL. Methods: Five children with asymptomatic congenital CMV infection and seven children with GJB2 mutation-related SNHL, with and without developmental disorder, underwent cochlear implantation. Hearing level and speech and language development were evaluated post-implantation using IT-MAIS, MUSS, and S-S method. Results: The IT-MAIS and MUSS scores of the congenital CMV infection group and the GJB2 mutation group continued to increase for 4 years after implantation. The S-S method score in both groups gradually increased, although the scores for children with mental retardation were low. [ABSTRACT FROM AUTHOR]

Mutations of the GJB2 gene, encoding Connexin 26, are the most common cause of hereditary congenital hearing loss in many countries, and account for up to 50% of cases of autosomal-recessive non-syndromic deafness. By contrast, only a few GJB2 mutations have been reported to cause an autosomal-dominant form of non-syndromic deafness. We report on a family from southern Italy in whom dominant, non-syndromic, post-lingual hearing loss is associated with a novel missense mutation in the GJB2 gene. Direct sequencing of the gene showed a heterozygous G→A transition at nucleotide 535, resulting in an aspartic acid to asparagine amino acid substitution at codon 179 (D179N). This mutation occurred in the second extracellular domain (EC2), which would seem to be very important for connexon–connexon interaction. [ABSTRACT FROM AUTHOR]