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In the cochlea, connexin 26 (Cx26) and connexin 30 (Cx30) co‐assemble into two types of homomeric and heteromeric gap junctions between adjacent non‐sensory epithelial cells. These channels provide a mechanical coupling between connected cells, and their activity is critical to maintain cochlear homeostasis. Many of the mutations in GJB2 or GJB6, which encode Cx26 and Cx30 in humans, impair the formation of membrane channels and cause autosomal syndromic and non‐syndromic hearing loss. Thus, deciphering the connexin trafficking pathways in situ should represent a major step forward in understanding the pathogenic significance of many of these mutations. A growing body of evidence now suggests that Cx26/Cx30 heteromeric and Cx30 homomeric channels display distinct assembly mechanisms. Here, we review the most recent advances that have been made toward unraveling the biogenesis and stability of these gap junctions in the cochlea. Key Findings: Cx26/Cx30 heteromeric and Cx30 homomeric channels display distinct assembly mechanismsCadherin‐based tricellular adherens junctions promote the microtubule‐mediated trafficking of Cx26/Cx30 oligomers to the cell surface and further assembly into GJPsEphrin‐B2 promotes the assembly and sequestration of Cx30 GJPs into caveolae membrane domains in a cell‐autonomous manner [ABSTRACT FROM AUTHOR]

Intercellular communication via gap junctions (GJs) has a wide variety of complex and essential functions in the CNS. In the present developmental study, we aimed to quantify the number of astrocytic GJs protein connexin 30 (Cx30) of genetic model of absence epilepsy rats from Strasbourg (GAERS) at postnatal P10, P30, and P60 days in the epileptic focal areas involved in the cortico‐thalamic circuit. We compared the results with Wistar rats using immunohistochemistry and western blotting. The number of Cx30 immunopositive astrocytes per unit area were quantified for the somatosensory cortex (SSCx), ventrobasal (VB), and lateral geniculate (LGN) thalamic nuclei of the two strains and Cx30 western blot was applied to the tissue samples from the same regions. Both immunohistochemical and western blot results revealed the presence of Cx30 in all regions studied at P10 in both Wistar and GAERS animals. The SSCx, VB, and LGN of Wistar animals showed progressive increase in the number of Cx30 immunopositive labeled astrocytes from P10 to P30 and reached a peak at P30; then a significant decline was observed from P30 to P60 for the SSCx and VB. However, in GAERS Cx30 immunopositive labeled astrocytes showed a progressive increase from P10 to P60 for all brain regions studied. The immunohistochemical data highly corresponded with western blotting results. We conclude that the developmental disproportional expression of Cx30 in the epileptic focal areas in GAERS may be related to the onset of absence seizures or may be related to the neurogenesis of absence epilepsy. [ABSTRACT FROM AUTHOR]

The article discusses the use of shared genetic testing algorithm in patients with sensorineural hearing loss (SNHL). It states that 221 adult and 163 with nonsyndromic SNHL from University of Miami Ear Institute were tested. It concludes that testing on mutations in gap junction beta-2 (GJB2) and gap junction beta-6 (GJB6), mitochondrial DNA, and peripheral blood samples could help in the etiologic diagnosis of SNHL.

Objectives: The aim of the study is to assess clinical characteristics of individuals with nonsyndromic sensorineural hearing loss (NSSNHL) with genetic mutations in GJB2 and/or GJB6. We describe and compare one group with biallelic mutations against a group of heterozygote mutation carriers. Methods: A total of 350 patients between the ages of 3 months and 80 years referred to a tertiary care outpatient otology practice for NSSNHL were screened for genetic mutations. Direct sequencing of GJB2 and polymerase chain reaction analysis of GJB6 was performed and clinical data from history and physical, audiologic testing and radiographic studies were reviewed. Results: Thirty-two patients were found to have biallelic mutations (incidence of 9.1%). Twenty-five patients were found to have only one GJB2 mutation (incidence of 7.1%). Severe to profound hearing loss occurred in 85% of the homozygote group and 38% of the heterozygote group. Both groups similarly had a propensity toward bilateral, symmetric, nonprogressive hearing loss with rare inner ear malformations on radiologic imaging. Conclusions: These two patient populations have similar incidences in a cohort of patients evaluated for NSSNHL, which is higher than general population heterozygote carrier rates. Heterozygote mutation carriers had less hearing impairment, but most other factors demonstrated no differences. These results support the theory of an unidentified genetic factor contributing to hearing loss in some heterozygote carriers. Therefore, genetic counseling should consider the complexity of their genetic factors and the limitations of current screening. [ABSTRACT FROM AUTHOR]

Wilch E, Azaiez H, Fisher RA, Elfenbein J, Murgia A, Birkenhäger R, Bolz HJ, da Silva-Costa SM, del Castillo I, Haaf T, Hoefsloot L, Kremer H, Kubisch C, Le Marechal C, Pandya A, Sartorato EL, Schneider E, Van Camp G, Wuyts W, Smith RJH, Friderici KH. A novel DFNB1 deletion allele supports the existence of a distant cis-regulatory region that controls GJB2 and GJB6 expression. Eleven affected members of a large German–American family segregating recessively inherited, congenital, non-syndromic sensorineural hearing loss (SNHL) were found to be homozygous for the common 35delG mutation of GJB2, the gene encoding the gap junction protein Connexin 26. Surprisingly, four additional family members with bilateral profound SNHL carried only a single 35delG mutation. Previously, we demonstrated reduced expression of both GJB2 and GJB6 mRNA from the allele carried in trans with that bearing the 35delG mutation in these four persons. Using array comparative genome hybridization (array CGH), we have now identified on this allele a deletion of 131.4 kb whose proximal breakpoint lies more than 100 kb upstream of the transcriptional start sites of GJB2 and GJB6. This deletion, del(chr13:19,837,344–19,968,698), segregates as a completely penetrant DFNB1 allele in this family. It is not present in 528 persons with SNHL and monoallelic mutation of GJB2 or GJB6, and we have not identified any other candidate pathogenic copy number variation by arrayCGH in a subset of 10 such persons. Characterization of distant GJB2/GJB6 cis-regulatory regions evidenced by this allele may be required to find the ‘missing’ DFNB1 mutations that are believed to exist. [ABSTRACT FROM AUTHOR]

Objectives/Hypothesis: Connexin 26 is a gap junction protein encoded by the GJB2 gene. It is expressed in cholesteatoma, and mutations cause proliferative skin disorders and sensorineural hearing loss (SNHL). Deletions of GJB6, which encodes connexin 30, cause SNHL in a digenic manner with a heterozygous GJB2 mutation. We hypothesize that GJB2 and GJB6 mutations might influence the development of cholesteatoma. Study Design: Prospective observational study to identify GJB mutations in pediatric cholesteatoma. Methods: Peripheral blood samples from 98 children with cholesteatoma were screened for mutations in the GJB2 gene by direct sequencing of the coding region (exon 2 and the intron/exon boundary). Deletions of the GJB6 gene were tested using multiple ligation probe amplification methods. GJB status was compared with other populations and patient age and extent of cholesteatoma at presentation. Results: Fourteen children had at least one GJB2 variant (14%). Of these, three had two variants. Two of the variants were neutral polymorphisms. One child with the GJB2 genotype 35delG/35delG also had SNHL. No correlation was found between GJB2 status and patient age or cholesteatoma severity at presentation. No GJB6 deletions were found. Conclusions: GJB2 gene variants are present in a minority of children with cholesteatoma, but may be more common than in normal populations. It is conceivable that alterations of connexin 26 expression could contribute to the multifactorial disease process in cholesteatoma by modifying the cell-to-cell communication that is important in proliferation and migration of keratinocytes. Laryngoscope, 2010 [ABSTRACT FROM AUTHOR]

Objectives/Hypothesis: The aim of this study was to 1) determine the prevalence of DFNB1 in a cohort of children with prelingual nonsyndromic sensorineural hearing loss (HL), 2) study phenotype/genotype correlations, and 3) establish guidelines for genetic counseling of DFNB1. Study Design: Prospective cohort study. Methods: A total of 119 unrelated children (107 sporadic and 12 familial cases) with prelingual nonsyndromic HL underwent mutational screening for DFNB1 in the noncoding and coding exons of GJB2, in addition to the del( GJB6-D13S1830) mutation of GJB6. Information regarding demographics, HL, developmental milestones, inner ear high resolution computed tomography, hearing habilitation, and associated phenotypic manifestations were collected in probands with biallelic pathogenic mutations. Results: The prevalence of DFNB1 in cases of prelingual nonsyndromic HL was 26% (25% in sporadic and 50% in familial cases). In regards to ethnicity, 19 probands were white and 12 probands of Hispanic ancestry had a mixed racial origin (black, Native-American, white). Greater allelic heterogeneity was shown with Hispanics of mixed descent exhibiting 10 of 12 GJB2 allelic variants, whereas whites had 4 of 10 allelic variants (Fisher exact test, P = .033); both ethnic groups had the GJB6 deletion. The frequency of deaf carriers of the most commonly found mutation (c.35delG) was 8% and higher than that of expected for the general population (Fisher exact test, P = .015). The hearing phenotype was variable in terms of degree of impairment (from mild to profound),onset, symmetry and progression, and there was no correlation with any specific genotype class. DFNB1 probandshad normal gross motor development, and the frequency of computed tomography abnormalities of the inner ear was low at 8%. No other specific associated phenotypic manifestations were identified. Conclusions: DFNB1 is the most common identifiable etiology of nonsyndromic prelingual deafness both in sporadic and familial cases in this cohort with ethnic diversity. The greater allelic variability observed in Hispanics and the high frequency of deaf probands carrying a single allelic variant of DFNB1 support extending the screening to noncoding regions of GJB2 and to the remaining DFNB1 locus. Most probands have a congenital HL that is stable, symmetrical and without associated manifestations, but the audiometric profile should not be the only criteria for offering mutational screening of DFNB1 because of the observed variability. These data can be applied to direct the clinical evaluation and effectively counsel families of children with DFNB1. [ABSTRACT FROM AUTHOR]

Mutations in theGJB2gene are the most common cause of prelingual, autosomal recessive, sensorineural hearing loss worldwide. Nevertheless, 10% to 50% of patients with prelingual nonsyndromic deafness only carry one mutation in theGJB2gene. Recently a large 342 kb deletion namedΔ(GJB6-D13S1830) involving theGJB6gene was reported in Spanish and French deafness patients, either in a homozygous state or in combination with a monoallelicGJB2mutation. No data have been reported about the frequency of this mutation in central Europe.Thirteen Czech patients with prelingual nonsyndromic sensorineural deafness carrying only one pathogenic mutation in theGJB2gene were tested for the presence of theΔ(GJB6-D13S1830) mutation. One patient with aGJB2mutation (313del14) also carried theΔ(GJB6-D13S1830). This is the first reported Czech case, and probably also the first central European case, of prelingual deafness due to mutations involving both theGJB2andGJB6genes. In addition, theΔ(GJB6-D13S1830) was not detected in 600 control chromosomes from Czech individuals with normal hearing. We show that in the Czech Republic theΔ(GJB6-D13S1830) is not the second most common causal factor in deafness patients heterozygous for a singleGJB2mutation, and thatΔ(GJB6-D13S1830) is very rare in central Europe compared to reports from Spain, France and Israel. [ABSTRACT FROM AUTHOR]

Background: In the present study, we investigate the prevalence of the GJB2 gene mutations, and deletions in the GJB6 gene, namely del (GJB6‐D13S1830) and del (GJB6‐D13S1854), in patients with autosomal recessive non‐syndromic hearing loss (ARNSHL) from the central region of Iran. Methods: One hundred and thirty‐one unrelated ARNSHL cases from the central part of Iran were recruited. Among them, 81% (106 cases) had at least two affected relatives. Coding and noncoding regions of the GJB2 gene were sequenced. Multiplex PCR was used for analysis of del (GJB6‐D13S1830) and del (GJB6‐D13S1854) deletions in GJB6. Results: The GJB2 variants were found in 16.79% (22/131) of the patients. The pathogenic variants were 21/131 (16.03%). The nonpathogenic variants were 1/131 (0. 07%). Allele frequency of the c.35delG as the pathogenic variant was the most common with 59.52% (25/42). The remaining pathogenic variants were c.235delC, p.T8M, p.R32H, p.R143Q, p.R143W, c‐23+1G>A. The only nonpathogenic variant was polymorphism p.V27I. Further segregation analysis showed that variant of p.R143Q might have incomplete penetrance. None of the patients had targeted deletions in the GJB6 gene. Conclusion: In comparison with reports from other areas of Iran, c.35delG demonstrates the highest frequency within the central region (accounting for 57.14% of cases), probably resulting from the founder effect and consanguineous marriage. The pathology of ARNSHL in such patients could be attributed to defects in Connexin 26 encoded by GJB2. [ABSTRACT FROM AUTHOR]

Background: Hidrotic ectodermal dysplasia (HED), also named as Clouston syndrome, is a rare autosomal dominant disease. Mutations in GJB6, GJB2 and GJA1 are related to HED., Objective: Summarize the clinical feature and analyse the mutation of the GJB6 gene in a large Chinese family with HED., Methods: We collected a very large Chinese family with HED. Clinical information was analysed. Blood samples were obtained. The whole coding region of GJB6 was amplified by polymerase chain reaction and sequenced. The results were further confirmed at mRNA level by reverse transcription polymerase chain reaction., Results: Sequence analysis identified a heterozygous missense mutation c.263C>T (p.A88V) in genomic DNAs of 25 patients, and this mutation was excluded from 14 normal individuals in this HED family and 218 unrelated, population-matched control individuals. The transcription of mutated allele was confirmed by RT-PCR of Cx30 mRNA from proband(,) s scalp skin. We found a novel phenotype of this variant in this Chinese HED family., Conclusion: Our data reveals that a recurrent mutation p.A88V in GJB6 played a pathogenic role in a large Chinese family and emphasizes the importance of gene test in this congenital disorder., (© 2016 European Academy of Dermatology and Venereology.)

Mutations in the gap-junction gene Cx30 (Connexin30, GJB6) are a known cause of hearing loss. Here, we report our findings on a large multigeneration family in which severe to profound sensorineural hearing impairment is associated with a variety of skin-related anomalies. Genome-wide analysis of the family showed that the locus maps to chromosome region 13ptel-q12.1 and that a novel mutation, p.N54K, in Cx30, cosegregates with the phenotype. Unlike wild-type Cx30, p.N54K Cx30 is predominantly localized in the cytoplasm and does not permit transfer of neurobiotin, suggesting improper cellular localization and abolishment of gap-junction activity., (© 2015 John Wiley & Sons Ltd/University College London.)

Mutations in the GJB2 gene encoding the gap junction protein Connexin 26 have been associated with autosomal recessive as well as dominant nonsyndromic hearing loss. Owing to the involvement of connexins in skin homeostasis, GJB2 mutations have also been associated with syndromic forms of hearing loss showing various skin manifestations. We report an assortatively mating hearing impaired family of south Indian origin with three affected members spread over two generations, having p.R75Q mutation in the GJB2 gene in the heterozygous condition. The inheritance pattern was autosomal dominant with mother and son being affected. Dermatological and histopathologic examinations showed absence of palmoplantar keratoderma. To the best of our knowledge, this is the first report from India on p.R75Q mutation in the GJB2 gene with nonsyndromic hearing loss., (© 2014 John Wiley & Sons Ltd/University College London.)

Objectives/hypothesis: Congenital deafness occurs in approximately 1 in 1,000 live births, and 50% of these cases are hereditary. Connexin mutations have been identified as the most common cause of hereditary hearing loss in many populations. The prevalence of this mutation in African patients has not been adequately studied. The objective of this study was to determine the prevalence of connexin 26 and 30 mutations in a population of hearing-impaired patients from Uganda., Study Design: This is an observational study., Methods: Coding regions of both GJB2 and GJB6, noncoding exon 1 of GJB2, and 30 nucleotides of intronic sequence bordering the exons were analyzed in 126 subjects from Uganda with confirmed bilateral, severe-to-profound sensorineural hearing loss. All variants were analyzed for possible clinical significance using a combination of database searches and in silico tools., Results: Complete sequence data were obtained on 115/126 individuals; 11 had only partial or no results. Only one reported pathogenic variant was found in GJB2 (c.208C>G; p.Pro70Ala) and none in GJB6. Three reported variants and two novel variants within intron 1 of GJB2 and two variants within exon 3 of GJB6 were also found., Conclusions: None of the most common types of deletions in the GJB2 gene (c.35delG, c.167delT or c.235delC) were found in this large cohort of deaf children from Uganda. This prompts a search for genetic causes of deafness among this and other previously studied African populations., (© 2014 The American Laryngological, Rhinological and Otological Society, Inc.)

Expression of connexin26 (Cx26), Cx30 and Cx43 in astrocytes and expression of Cx29, Cx32 and Cx47 in oligodendrocytes of adult rodent brain has been well documented, as has the interdependence of connexin expression patterns of macroglial cells in Cx32- and Cx47-knockout mice. To investigate this interdependence further, we examined immunofluorescence labelling of glial connexins in transgenic Cx30 null mice. Ablation of astrocytic Cx30, confirmed by the absence of immunolabelling for this connexin in all brain regions, resulted in the loss of its coupling partner Cx32 on the oligodendrocyte side of astrocyte-oligodendrocyte (A/O) gap junctions, but had no effect on the localization of astrocytic Cx43 and oligodendrocytic Cx47 at these junctions or on the distribution of Cx32 along myelinated fibres. Surprisingly, gene deletion of Cx30 led to the near total elimination of immunofluorescence labelling for Cx26 in all leptomeningeal tissues covering brain surfaces as well as in astrocytes of brain parenchyma. Moreover northern blot analysis revealed downregulation of Cx26 mRNA in Cx30-knockout brains. Our results support earlier observations on the interdependency of Cx30/Cx32 targeting to A/O gap junctions and further suggest that Cx26 mRNA expression is affected by Cx30 gene expression. In addition, Cx30 protein may be required for co-stabilization of gap junctions or for co-trafficking in cells., (© 2011 The Authors. European Journal of Neuroscience © 2011 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.)

There are limited data on the impact of incorporating genetic counseling and testing into the newborn hearing screening process. We report on results from a prospective, longitudinal study to determine the impact of genetic counseling and GJB2/GJB6 genetic testing on parental knowledge, attitudes, and beliefs about genetic testing. One hundred thirty culturally hearing parents of 93 deaf or hard-of-hearing children ages 0-3 years primarily identified through newborn hearing screening received pre- and post-test genetic counseling for GJB2 and GJB6. Parents completed questionnaires following pre-test counseling, and 1- and 6-month post-test result disclosure. Results indicate that following pre-test counseling all parents perceived benefits to genetic testing. While parents who received positive results continued to perceive benefits from testing, perceived benefit declined among parents who received inconclusive or negative results. Parents did not perceive genetic testing as harmful following pre-test counseling or receipt of test results. Parents who received positive test results performed better in understanding recurrence and causation of their child's deafness and indicated greater interest in prenatal genetic testing than those who received inconclusive or negative test results. Parents felt that pediatricians and audiologists should inform parents of genetic testing availability; however, there was no consensus on timing of this discussion. Thus culturally hearing parents do not perceive genetic testing of their deaf or hard-of-hearing infants/toddlers as harmful; they feel that primary care providers should discuss genetic testing with them; and positive genetic test results with genetic counseling give rise to better understanding and perceived benefit than negative or inconclusive results., ((c) 2009 Wiley-Liss, Inc.)

Objectives: Connexin proteins play an important role in cell-to-cell communication. Mutations in the genes that encode for these connexins may potentially lead to dysfunction in mucociliary clearance predisposing to chronic rhinosinusitis (CRS) or recurrent acute rhinosinusitis (RARS). The objective of this study was to assess for the presence of connexin 26 and 30 gene mutations in patients with CRS and RARS., Study Design: Prospective case series., Methods: Forty-six consecutive patients who were diagnosed with CRS or RARS at a single tertiary care facility were included in the study. Patients with known dysfunction in mucociliary clearance were excluded. The following clinical data were collected: age, gender, duration of disease and age at onset, personal history of otitis media and/or sensorineural hearing loss (SNHL), and family history of paranasal sinus disease and SNHL. Buccal swab deoxyribonucleic acid (DNA) specimens were sequenced for connexin 26 and 30 genes., Results: The study group consisted of 32 females and 14 males, 8 children and 38 adults. Adequate sequencing of connexin 30 gene was possible in all 46 specimens, but in only 19 specimens for connexin 26 gene. Connexin 30 gene mutations were not detected in any of the 46 specimens. Two of the 19 specimens had heterozygous mutations in the connexin 26 gene; there was one V371 mutation and one 35dG mutation. Both patients were adults; the patient with 35dG mutation had SNHL., Conclusion: Mutations in connexin 26 and 30 genes are rare in patients with CRS or RARS and do not seem to play a contributory role in the pathogensis of these disorders.

The most common form of non-syndromic autosomal recessive deafness (NSRD) is caused by mutations in the GJB2 gene. Recently, a deletion truncating the GJB6 gene, called del(GJB6-D13S1,830) has also been described normally accompanying mutations in another allele of the GJB2 gene. Among all the mutations described to date, 35delG in the GJB2 gene is the most common. Preliminary data suggest that pathologic changes due to GJB2 mutations do not affect the spiral ganglion cells, which are the site of stimulation of the cochlear implant. Besides, the survival of the spiral ganglion cells is believed to be an important determinant of the outcome after surgery. Therefore, we have studied 49 non-syndromic deaf patients with unknown etiologies in order to determine the prevalence of GJB2 and GJB6 gene mutations in patients undergoing cochlear implantation surgery. Also, the molecular studies were performed using polymerase chain reaction amplification and direct sequencing. As a result, we found 19 individuals with GJB2 mutation including one new mutation (K168R), one patient homozygous for the del(GJB6-D13S1,830). These results establish that genetic screening can provide an etiologic diagnosis, and may help with prognosis after cochlear implantation, as has been hypothesized in previous studies., ((c) 2007 Wiley-Liss, Inc)

Hereditary hearing loss is a complex disorder that involves a large number of genes. In developed countries, 1 in 1,000 children is born with deafness severe enough to require special education services, and about 60% of the cases of isolated deafness have a genetic origin. Although more than 100 genes for hearing loss are known currently, only a few are routinely tested in the clinical practice. In this study, we present our findings from the molecular diagnostic screening of the GJB2 and GJB3 genes, del(GJB6-D13S1,830) and del(GJB6-D13S1,854) deletions in the GJB6 gene, Q829X mutation in the otoferlin gene (OTOF) and, the A1,555G and A7,445G mutations in the mitochondrial genome over an 8-year period. Mutations analysis in the previously mentioned genes and mutations was performed on 645 unrelated Brazilian patients with hearing loss who fell into two different testing groups. Different mutations in the GJB2 gene were responsible for most of cases studied, but deletions in the GJB6 gene as well as mitochondrial mutations were also found. While most cases of hearing loss in this country are due to environmental factors, the genetic etiology of deafness will increasingly be determined as more genetic tests become available., ((c) 2007 Wiley-Liss, Inc)

Autosomal recessive nonsyndromic sensorineural hearing impairment (ARNSHI) comprises 80% of familial hearing loss cases. Approximately half result from mutations in the connexin 26 (Cx26) gene, GJB2, in Caucasian populations. Heterozygous mutations in GJB2 occasionally co-occur with a deletion of part of GJB6 (connexin 30; Cx30). It is estimated that approximately 1% of deafness is maternally inherited, due to mutations in mitochondrial DNA (mtDNA). Few studies have focused on the frequency of mutations in connexins or mtDNA in African American (AA) and Caribbean Hispanic (CH) admixture populations. In this study, we performed bidirectional sequencing of the GJB2 gene and polymerase chain reaction (PCR) screening for the common GJB6 deletion, as well as PCR/RFLP analysis for three mutations in mtDNA (A1555G, A3243G, A7445G), in 109 predominantly simplex AA and CH individuals. Variations found were a 101T > C (M34T; 1/101 cases), 109G > A (V37I; 1/101), 35delG (mutation; 4/101, (3/4) of non-AA/CH ethnicity), 167delT (mutation; 1/101), 139G > T (mutation; E47X; 1/101 homozygote, consanguineous), -15C > T (1/101), 79G > A (V27I; 9/101), 380G > A (R127H; 4/101; Guyana, India, Pakistan ethnicity), 670A > C (Indeterminate; K224Q; 1/101), 503A > G (novel; K168R; 3/101) and 684C > A (novel; 1/101). All but one of the AA and CH patients had monoallelic variations. There were no hemizygous GJB6 deletions in those with monoallelic GJB2 variations. We also did not identify any patients with the three mutations in mtDNA. Bidirectional sequencing of the GJB2 gene was performed in 187 AA and Hispanic healthy individuals. Our results reveal that GJB2 mutations, GJB6 deletions, and mtDNA mutations may not be significant in these minority admixture populations., (Copyright 2007 Wiley-Liss, Inc.)

Genetic and auditory studies of 731 children with severe-to-profound hearing loss in US schools for the deaf and 46 additional children receiving clinical services for hearing loss ranging from moderate to profound demonstrated that mutations in the connexin 26 (GJB2) and connexin 30 (GJB6) genes explain at least 12% of those with nonsyndromic sensorineural deafness. Otoacoustic emissions (OAEs) testing to detect functional outer hair cells indicated that 76 of the children had emissions and therefore may have (as yet unconfirmed) auditory neuropathy/dys-synchrony (AN/AD). Five of these children with OAEs were GJB2 homozygotes or compound heterozygotes with the genotypes 35delG/35delG, W77X/W77X, 35delG/360delGAG, 35delG/V95M, and V84M/M34T. In particular, unilateral AN/AD was confirmed in a child with moderate hearing loss and the 35delG/V95M genotype. Detecting OAEs in individuals with GJB2 mutations suggests that lack of functional gap junctions as a result of GJB2 mutations does not necessarily destroy all outer hair cell function.

Objectives/hypothesis: Hearing impairment has a high prevalence affecting approximately 1 in 1000 newborn children. Alterations in the gap junction protein beta 2 (GJB2) and gap junction protein beta 6 (GJB6) are associated with nonsyndromic hearing impairment and should have a significant impact on genetic counseling., Study Design: Various cases of nonsyndromic hearing impairment were screened for alterations in GJB2 and GJB6 in this clinical study., Methods: The prevalence of mutations in GJB2 encoding for connexin 26 in a patient group with nonsyndromic hearing impairment comprising 45 families and 57 sporadic cases was initially determined by sequencing. The role of GJB2 was then assessed in individuals with hearing impairment (3 families and 20 sporadic cases) who are usually excluded from analysis because of the presence of additional symptoms or in cases in which a role for nongenetic factors cannot be eliminated. In hearing-impaired individuals with heterozygous GJB2 mutations the recently identified 342-kb deletion truncating GJB6 called del(GJB6-D13S1830) as a digenetic component in hearing impairment was excluded by polymerase chain reaction., Results: Autosomal recessively inherited GJB2 mutations induced hearing impairment in 25.5% of individuals in the nonsyndromic hearing impairment group. GJB2 alterations were also seen in 17.4% of individuals in whom additional symptoms or a role for nongenetic involvement could not be excluded. In all, 15 different alterations in GJB2 were detected, including the previously unknown 154G>C, 557C>T, and 682C>T mutations, and these were correlated to clinical parameters., Conclusion: Improved genetic counseling can be performed by screening for GJB2 alterations in patients with nonsyndromic hearing impairment including patients within groups for which a role for exogenetic factors cannot be excluded. Specific genetic counseling for GJB2-linked hearing impairment in heterozygotes will depend on future research.

Recent investigations identified a large deletion of the GJB6 gene in trans to a mutation of GJB2 in deaf patients. We looked for GJB2 mutations and GJB6 deletions in 255 French patients presenting with a phenotype compatible with DFNB1. 32% of the patients had biallelic GJB2 mutations and 6% were a heterozygous for a GJB2 mutation and a GJB6 deletion. Biallelic GJB2 mutations and combined GJB2/GJB6 anomalies were more frequent in profoundly deaf children. Based on these results, we are now assessing GJB6 deletion status in cases of prelingual hearing loss., (Copyright 2004 Wiley-Liss, Inc.)

Objectives/hypothesis: Mutations in the connexin 26 (Cx26) or gap junction beta 2 gene are the leading cause of hereditary nonsyndromic sensorineural hearing loss in Caucasians. The Cx26 coding region of 68 children with nonsyndromic sensorineural hearing loss was sequenced to determine the frequency and type of Cx26 mutations in this population. Screening was also performed for a common connexin 30 (Cx30) or gap junction beta 6 mutation (del [GJB6-D13S1830]). Children also underwent audiological testing to determine whether any correlation exists between Cx26 mutations and severity of hearing loss., Study Design: In all, 68 children with nonsyndromic sensorineural hearing loss were screened for Cx26 and Cx30 mutations by polymerase chain reaction and direct sequencing., Methods: Genomic DNA was amplified by polymerase chain reaction using primers that flank the entire Cx26 coding region. Screening for the 342-kb Cx30 deletion was performed using primers that amplified the breakpoint junction of the deletion. The amplicons were then sequenced in both directions and analyzed for mutations. Audiometric testing, including pure-tone audiometry and auditory evoked brainstem response, was also performed to determine the degree of hearing loss., Results: Twenty-seven of 68 children tested had mutations in Cx26 with 35delG being the most prevalent. Ten additional Cx26 mutations were detected including a novel compound heterozygote. Two children were heterozygous for the Cx30 del (GJB6-D13S1830) mutation., Conclusion: Cx26 and Cx30 mutations were present in 41.2% of children tested in the study population. Audiometric data supported previous studies demonstrating a greater degree of hearing loss in subjects who are homozygous for the 35delG mutation.

Hearing loss is a common congenital disorder that is frequently associated with mutations in the Cx26 gene (GJB2). Three recent reports that found a large deletion in another DFNB1 gene, Cx30 (GJB6), suggest that this defect may cause nonsyndromic recessive hearing loss through either a homozygous deletion of Cx30, or digenic inheritance of a Cx30 deletion and a Cx26 mutation in trans. We designed a simple diagnostic strategy with multiplex PCR followed by direct sequencing to allow for the simultaneous detection of Cx26 mutations and Cx30 deletions, and evaluated its effectiveness as a clinical genetic test by examining 200 DNA samples. In the 108 samples from deaf subjects, two digenic mutations were identified in Cx26 and Cx30 (E47X/342 kb deletion and 167delT/342 kb deletion); 69 had only Cx26 mutations (29 biallelic, 40 singleton), including two novel frameshift mutations 511-512insAACG and 358-360delAG; and 37 had no detectable mutation in either Cx26 or Cx30. Our deletion mapping suggested that the proximal breakpoint of all reported Cx30 large deletions are between the nucleotide 444 and 627 at the Cx30 coding region within a maximal interval of 78 or 184 bp. This simultaneous examination of Cx26 and Cx30 is a practical and efficient diagnostic approach for patients with nonsyndromic congenital deafness., (Copyright 2003 Wiley-Liss, Inc.)

Gap-junction channels in the brain, formed by connexin (Cx) proteins with a distinct regional/cell-type distribution, allow intercellular electrical and metabolic communication. In astrocytes, mainly the connexins 43, 26 and 30 are expressed. In addition, connexin30 is expressed in ependymal and leptomeningeal cells, as well as in skin and cochlea. The functional implications of the astrocytic gap-junctional network are not well understood and evidence regarding their behavioural relevance is lacking. Thus, we have tested groups of Cx30-/-, Cx30+/-, and Cx30+/+ mice in the open-field, an object exploration task, in the graded anxiety test and on the rotarod. The Cx30-/- mice showed reduced exploratory activity in terms of rearings but not locomotion in the open-field and object exploration task. Furthermore, Cx30-/- mice exhibited anxiogenic behaviour as shown by higher open-field centre avoidance and corner preference. Graded anxiety test and rotarod performance was similar across groups. The Cx30-/- mice had elevated choline levels in the ventral striatum, possibly related to their aberrant behavioural phenotypes. The Cx30+/- mice had lower dopamine and metabolite levels in the amygdala and ventral striatum and lower hippocampal 5-hydroxyindole acid (5-HIAA) concentrations relative to Cx30+/+ mice. Furthermore, the Cx30+/- mice had lower acetylcholine concentrations in the ventral striatum and higher choline levels in the neostriatum, relative to Cx30+/+ mice. Our data suggest that the elimination of connexin30 can alter the reactivity to novel environments, pointing to the importance of gap-junctional signalling in behavioural processes.