Hearing impairment in Dutch patients with connexin 26 (GJB2) and connexin 30 (GJB6) mutations

OBJECTIVE: Despite the identification of mutations in the connexin 26 (GJB2) gene as the most common cause of recessive nonsyndromic hearing loss, the pattern of hearing impairment with these mutations remains inconsistent. Recently a deletion encompassing the GJB6 gene was identified and hypothesized to also contribute to hearing loss. We hereby describe the hearing impairment in Dutch patients with biallelic connexin 26 (GJB2) and GJB2+connexin 30 (GJB6) mutations. METHODS: The audiograms of patients who were screened for GJB2 and GJB6 mutations were analysed retrospectively. Standard statistical testing was done for symmetry and shape, while repeated measurement analysis was used to assess the relation between mutation and severity. Progression was also studied via linear regression analysis. RESULTS: Of 222 hearing-impaired individuals, 35 exhibited sequence variations; of these 19 had audiograms for study. Hearing loss in patients with biallelic "radical" (i.e. deletions, nonsense and splice site) mutations was significantly worse than in the wild type and heterozygotes (SAS proc GENMOD, p=0.013). The presence of at least one missense mutation in compound heterozygotes tends to lead to better hearing thresholds compared to biallelic radical mutations (p=0.08). One patient with the [35delG]+[del(GJB6-D13S1830)] genotype was severely impaired. Non-progressive hearing impairment was demonstrated in five 35delG homozygotes in individual longitudinal analyses. However a patient with the [299A>C]+[416G>A] genotype showed significant threshold progression in the lower frequencies. Findings on asymmetry and shape were inconclusive. CONCLUSIONS: Our data support the hypothesis that severity is a function of genotype and its effect on the amino acid sequence. A bigger cohort is required to establish non-progressivity more definitively.     

Longitudinal phenotypic analysis in patients with connexin 26 (GJB2) (DFNB1) and connexin 30 (GJB6) mutations

In 15 Belgian subjects with prelingual sensorineural hearing impairment, the connexin 26 (GJB2) gene and the connexin 30 (GJB6) gene were analyzed for the presence of the 35delG mutation and the delta(GJB6-D13S1830) deletion first described by del Castillo et al in 2002. Seven patients were found to be homozygous for the 35delG mutation; 7 were combined heterozygotes for the 35delG mutation and the GJB6 deletion. In 11 subjects, phenotype and genotype were correlated. Significant, transient progression, in the range of 1.7 to 2.7 dB/y, was only found in 2 patients in the first part of the second decade of life. Hearing impairment was otherwise stable, with mean thresholds of 75, 90, and 100 dB at 0.125, 0.25, and 0.5 kHz, respectively, and 100 dB or higher at 1 to 4 kHz. There was no significant difference in hearing impairment between the patients with the homozygous 35delG mutation in GJB2 and those who are heterozygous for both the 35delG mutation and the deletion encompassing part of GJB6.     

Auditory perception and speech discrimination after cochlear implantation in patients with connexin 26 (GJB2) gene-related deafness.

HYPOTHESIS: Auditory perception and speech discrimination among pediatric cochlear implantees may vary because of underlying deafness etiology, including connexin 26 (GJB2) gene-related deafness. BACKGROUND: Preliminary data suggest pathologic changes due to GJB2 mutations do not affect the spiral ganglion cells, which are stimulated by the cochlear implant. The survival of the spiral ganglion cells is believed to be an important determinant of outcome after surgery. Patients with GJB2-related deafness may therefore have enhanced prospects for good speech discrimination after implantation. METHODS: In an observational cohort study, GJB2 mutation analysis was performed using polymerase chain reaction amplification and direct sequencing on 31 prelingually deaf pediatric cochlear implantees, of which there were 30 with nonsyndromic deafness of unknown etiology, and one with keratitis-ichthyosis-deafness syndrome. Speech discrmination was assessed prospectively when they had reached postoperative year 3 using the IOWA Matrix Level B Sentences test and Glendonald Auditory Screening Procedure (GASP), with both patients and assessors blind to GJB2 status. RESULTS: Eleven patients had GJB2-related deafness and 20 patients had GJB2-unrelated deafness. IOWA Matrix scores were higher in patients with GJB2-related deafness but did not reach statistical significance. However, GASP scores were statistically significantly higher in patients with GJB2-related deafness (median word score, 92%; median sentence score, 80%), compared with those of patients with GJB2-unrelated deafness (median word score, 63%; median sentence score, 45%; word score, p = 0.037; sentence score, p = 0.045). Ordinal logistic regression analysis on IOWA Matrix and GASP sentence scores found better statistically significant scores in patients with GJB2-related deafness (p < 0.05) after adjustment for confounding variables. CONCLUSION: Pediatric cochlear implantees with GJB2-related deafness appear to have equal or better speech discrimination compared with a group of prelingually deaf children with deafness of unknown etiology.     

Ethnicity and mutations in GJB2 (connexin 26) and GJB6 (connexin 30) in a multi-cultural Canadian paediatric Cochlear Implant Program

OBJECTIVE: To determine the relationship between ethnicity and mutations in the GJB2 and GJB6 genes in multi-cultural patients enrolled in a Canadian paediatric Cochlear Implant Program. METHODS: Blood was analyzed from 65 paediatric cochlear implant users by direct sequencing of the coding region and intron/exon boundaries of the GBJ2 gene. Individuals heterozygous for one mutation in GJB2 or in whom mutations in GJB2 were not detected were analyzed for the common 342 kb deletion mutation D13S1830 in the GJB6 gene. Information regarding ethnicity of patients' families was obtained from patient records and/or interview. RESULTS: GJB2 mutations were found in 36.9% of paediatric cochlear implant users tested. Nine different GJB2 mutations were identified among individuals from 14 different countries of origin. Seventy-eight percent of all identified pathogenic GJB2 mutations were 35delG. Biallelic GJB2 mutations were found in 16 cochlear implant users (66.7% of GJB2 mutations). Three novel GJB2 sequence changes were identified: (1) a missense mutation T107C (L36P) in an individual of African decent; (2) a missense mutation G475T (D159Y) in an individual of Caribbean decent; (3) a regulatory region change 1-34C to T in an individual of African decent. GJB6-D13S1830 mutations were not found in any of the patients tested. Individuals of African, Caribbean and East Indian decent had different GJB2 mutations than the remainder of individuals tested. Patients of Asian, Italian, Spanish, Polish and Armenian decent were not found to carry mutations in GJB2 or the common GJB6-D13S1830 mutation. CONCLUSIONS: This study represents the largest number of biallelic GJB2 mutations isolated in a group of paediatric cochlear implant users to date. Numerous and diverse GJB2 mutations were found in this multi-cultural group of children. Even though GJB2 mutations have been widely reported in the literature, this discussion represents the first report of GJB2 mutations in a multi-ethnic population (Canadian), as compared with previous studies that investigated fairly homogeneous populations. The diversity of GJB2 mutations identified reinforces the importance of testing for changes in GJB2 by direct sequencing of the entire coding region rather than testing only for common mutations.     

Connexin 26 (GJB2) gene-related deafness and speech intelligibility after cochlear implantation.

HYPOTHESIS: Speech intelligibility in children after cochlear implantation may depend on their deafness cause, including connexin 26 (GJB2) gene-related deafness. BACKGROUND: There is significant variability in the degree of intelligibility, or clarity, of children's speech after cochlear implantation. GJB2 gene-related deafness may be a factor, as preliminary data suggest that pathologic changes do not affect the spiral ganglion cells, which are the neural elements stimulated by the implant, thus favoring better results. METHODS: In an observational retrospective cohort study of pediatric cochlear implantees, 38 patients with nonsyndromic deafness of unknown cause and 1 with keratitisichthyosis-deafness syndrome underwent GJB2 mutation analysis using polymerase chain reaction amplification and direct sequencing. The primary outcome measure assessed was Speech Intelligibility Rating score from postoperative Year 1 (n = 39) to Year 5 (n = 17). Educational setting was considered as a secondary outcome measure. Statistical analysis was double-blinded, with patients and assessors of outcome unaware of GJB2 status. RESULTS: Fourteen patients had GJB2-related deafness and 25 had GJB2-unrelated deafness. Comparisons at Year 3 (n = 31) revealed intelligible speech achieved by 9 of 11 with GJB2-related deafness, compared with only 6 of 20 with GJB2-unrelated deafness (p = 0.017). Ordinal logistic regression analysis on Speech Intelligibility Rating scores found statistically significantly better scores in children with GJB2-related deafness (p < 0.05) both before and after adjustment for confounding variables. A larger proportion with GJB2-related deafness also attended mainstream school (p = 0.01). CONCLUSION: In pediatric cochlear implantees, GJB2-related deafness is a predictor of good speech intelligibility.     

Molecular analysis of the GJB2, GJB6 and SLC26A4 genes in Korean deafness patients

OBJECTIVES: Mutations in the GJB2, GJB6 and SLC26A4 genes are a frequent cause of hearing loss in a number of populations. However, little is known about the genetic causes of hearing loss in the Korean population. METHODS: We sequenced the GJB2 and GJB6 genes to examine the role of mutations in these genes in 22 hearing loss patients. We also sequenced the SLC26A4 gene in seven patients with inner ear malformations, including enlarged vestibular aqueduct (EVA) revealed by computer tomography. RESULTS: Coding sequence mutations in GJB2 were identified in 13.6% of the patients screened. Two different mutations, 235delC and T86R were found in three unrelated patients. The 235delC was the most prevalent mutation with an allele frequency of 6.9% in our patient group. No mutations, including 342-kb deletion, were found in GJB6 gene. Three different variants of SLC26A4 were identified in the EVA patients, including one novel mutation. Four EVA patients carried two mutant alleles of SLC26A4, and at least one allele in all patients was the H723R mutation, which accounted for 75% of all mutant alleles. CONCLUSIONS: Our results suggest that GJB2 and SLC26A4 mutations together make up a major cause of congenital hearing loss in the Korean population. Further studies may be able to identify other common variants that account for a significant fraction of hearing loss in the Korean population.     

GJB2 (connexin 26) gene mutations in Moroccan patients with autosomal recessive non-syndromic hearing loss and carrier frequency of the common GJB2-35delG mutation

OBJECTIVE: Mutations in the connexin 26 gene (GJB2), which encodes a gap-junction protein expressed in the inner ear, have been shown to be responsible for a major part of autosomal recessive non-syndromic hearing loss in Caucasians. The aim of our study was to determine the prevalence and spectrum of GJB2 mutations, including the (GJB6-D13S1830) deletion, in Moroccan patients and estimate the carrier frequency of the 35delG mutation in the general population. METHODS: Genomic DNA was isolated from 81 unrelated Moroccan familial cases with moderate to profound autosomal recessive non-syndromic hearing loss and 113 Moroccan control individuals. Molecular studies were performed using PCR-Mediated Site Directed Mutagenesis assay, PCR and direct sequencing to screen for GJB2, 35delG and del(GJB6-D13S1830) mutations. RESULTS: GJB2 mutations were found in 43.20% of the deaf patients. Among these patients 35.80% were 35delG/35delG homozygous, 2.47% were 35delG/wt heterozygous, 3.70% were V37I/wt heterozygous, and 1 patient was E47X/35delG compound heterozygous. None of the patients with one or no GJB2 mutation displayed the common (GJB6-D13S1830) deletion. We found also that the carrier frequency of GJB2-35delG in the normal Moroccan population is 2.65%. CONCLUSIONS: These findings indicate that the GJB2-35delG mutation is the major cause of autosomal recessive non-syndromic hearing loss in Moroccan population. Two other mutations were also detected (V37I and E47X), in agreement with similar studies in other populations showing heterogeneity in the frequencies and types of mutation in connexin 26 gene.     

GJB2基因听力学表型与基因型关系分析

目的分析GJB2基因的听力学表型与基因型关系。方法 2007年4月²011年3月在解放军总医院就诊的具有完整听力学资料的1481名非综合征性耳聋患者,均进行GJB2编码区测序,并对其GJB2基因突变检出阳性率及与听力学表型关系进行统计学分析。结果 1481例患者GJB2基因阳性突变率为20.05%,双耳感音神经性聋组阳性突变率为20.66%,高于单耳耳聋组(2.08%)(P<0.01)。在双耳感音神经性聋组中,极重度聋组中的GJB2阳性检出率最高(26.07%),其次是重度(18.12%)、中度(17.4%),轻度组为11.54%,各组间阳性检出率差异有统计学意义(P<0.01)。对297例GJB2基因突变阳性患者听力曲线分型分析中,发现了10例上升型听力曲线(14.93%),但GJB2耳聋听力图仍以残余型(26.27%)、平坦型(25.16%)常见,各组阳性检出率差异有统计学意义(P<0.01)。结论 GJB2基因突变者听力学表型呈多样性,在进行基因检测时,除重视双耳重度、极重度感音神经性聋或听力图为残余型和平坦型的人群外,也应该对单耳耳聋、双耳轻度听力损失或听力图为上升型感音神经性聋患者进行常规耳聋基因检测。     

GJB2 gene mutations in childhood deafness

The frequency of childhood deafness is estimated at 1:1,000 and at least half of these cases are genetic. Recently, mutations in the GJB2 gene have been found in a great number of familial and sporadic cases of congenital deafness in Caucasians. The most common mutation (70%) is the frameshift mutation of a single guanine in position 35 (35delG). More than 20 mutations in the GJB2 gene are associated with DFNB1, a prevalent type of autosomal recessive non-syndromic neurosensory deafness. Last year we initiated a systematic screening programme to evaluate the causes of deafness in the population of prelingually deaf children who are referred to our cochlear implant programme. All of the deaf children and their parents undergo a comprehensive medical review, directed to identify causes of acquired deafness and manifestations of syndromic hearing impairment. DNA is extracted from the blood of all of the children. The technique AS-PCR (allele-specific polymerase chain reaction) is used for the identification of the mutation 35delG. Screening for other GJB2 gene mutations is carried out by single-strand conformation polymorphisms (SSCP). Our results on the identification of DFNB1 will be presented, as well as a discussion on the implications of an aetiological diagnosis in cochlear implantation.     

Temporal bone imaging in GJB2 deafness

OBJECTIVE: To describe temporal bone findings on computed tomography (CT) imaging in GJB2-related hearing loss (HL). We asked whether evaluation of the temporal bone is required in individuals with biallelic GJB2 mutations. STUDY DESIGN: Randomized, blinded, controlled, prospective measurement. METHODS: Blood from 264 pediatric cochlear implant users was analyzed for mutations in the GJB2 gene. Thirty-six aspects of the temporal bone on CT imaging were evaluated in 53 individuals (106 ears) with biallelic disease causing GJB2 mutations. A subset of patients was age matched and compared with normally hearing individuals. Subjects with biallelic GJB2 mutations were tested for mutations in the SLC26A4 gene to rule out Pendred syndrome as a confounding cause of large vestibular aqueduct syndrome. RESULTS: Approximately 53% of ears of subjects (72% of subjects) with biallelic GJB2 mutations had at least one temporal bone anomaly. The most common findings were 1) dilated endolymphatic fossa (28%); 2) hypoplastic modiolus (25%); 3) large vestibular aqueduct (8%); 4) hypoplastic horizontal semicircular canal (8%); 5) hypoplastic cochlea (4%). Compared with normally hearing individuals, the GJB2 group had hypoplasia of the cochlear nerve canal, lateral semicircular canal vestibule, internal auditory canal (t tests, P < .001), and were 11 times more likely to have a hypoplastic modiolus. Dilated endolymphatic fossae were 1.4 times more common in the GJB2 group, and large vestibular aqueducts were 3 times more common in the GJB2 group, as compared with normally hearing controls. CONCLUSIONS: Temporal bone anomalies are common in GJB2-related HL, and imaging of the temporal bone should be included in routine evaluation of these individuals.     

Audiological assessment of unilateral deafness

Unilateral deafness constitute medical (aetiological diagnosis, treatment, hearing aid fitting) and social problems (no certification of disability). Following audiological examinations were performed in the study: pure tone audiometry (PTA), impedance audiometry, auditory brainstem responses (ABR), otoacoustic emissions (OAE), as well as balance, taste, examinations and electric sensitivity of the acoustic nerve. In cases of tinnitus the parameters of its character were done. All of our patients underwent X-ray investigations, i.e. ear X-ray by Schüller and Stenvers methods, computerized tomography or magnetic resonance imaging. In some cases phoniatric and logopaedic examinations were performed. For aetiological diagnosis electrophoresis and immunological test (IgG and IgM against mumps) were carried out. The results were presented in two groups of patients with sudden and those of long lasting progressive unilateral deafness. Some of the patients were pharmacologically treated before the evaluation. It is concluded that the statistic analysis could be a basis for the management and prognosis of the unilateral deafness.     

Audiological and electrocochleography findings in hearing-impaired children with connexin 26 mutations and otoacoustic emissions

We recorded cochlear potentials by transtympanic electrocochleography (ECochG) in three hearing-impaired children with GJB2 mutation who showed otoacoustic emissions. Pure tone thresholds, distortion product otoacoustic emissions (DPOAEs) and, auditory brainstem responses (ABRs) were also obtained. Subjects 1 (35delG/35delG) and 3 (M34T/wt) had profound hearing loss and showed the picture of auditory neuropathy (AN) as DPOAEs were detected with absent ABRs in both ears. The hearing impairment found in subject 2 (35delG/35delG) was profound in the right ear and moderate in the left ear. Both DPOAEs and ABRs with normal latencies and morphology were recorded only from the left ear. On the ECochG recording the cochlear microphonic was obtained from all children. No compound action potential (CAP) was detected in subject 1. A neural response was recorded only from the left ear in subject 2 with a threshold corresponding to the audiometric threshold while no CAP was detected on the right side. The ECochG obtained from subject 3 showed a low-amplitude broad negative deflection which was identifiable down to low stimulus levels. This response decreased in amplitude and duration when utilizing a high-rate stimulation paradigm. The amount of amplitude reduction was close to that calculated for normal ears, thus revealing the presence of an adapting neural component. These findings indicate that patients with GJB2 mutations and preserved outer hair cells function could present with the picture of AN. The hearing impairment is underlain by a selective inner hair cell loss or a lesion involving the synapses and/or the auditory nerve terminals. We suggest that neonatal hyperbilirubinemia may play a role in protecting outer hair cells against the damage induced by GJB2 mutations.     

A novel connexin 26 mutation associated with autosomal recessive sensorineural deafness

Mutations in the connexin 26 (Cx26) gene (GJB2) are a common cause of hereditary hearing impairment which affects approximately 1 in 2000 newborn children. We report the identification of a novel Cx26 point mutation (439 G-->A) linked to familial, autosomal recessive, sensorineural hearing loss. This missense mutation (E147K) is located in the highly conserved, putative K(+) channel lining sequence of the third transmembrane domain (TM3) of Cx26. Hearing impairment associated with this mutation was congenital, moderate to profound and showed no signs of progressive deterioration.     

桥小脑角占位性病变的临床听力学表现

本文总结了经CT或MRI证实以及部分经手术证实的101例桥小脑角占位性病变的纯音测听，听性脑干反应（ABR），耳蜗电图（ECochG）以及前庭功能的表现。结果显示：ABR多表现为Ⅰ～Ⅴ间或延长（＞45ms），仅Ⅰ波存在或ABR各波均消失。未见波Ⅴ幅度小于波Ⅰ。当肿物较大时，可见时测ABR异常。极重度聋患者（35．5％），仍可引出异常ABR波形，故仍不可忽视ABR检查；听力轻度下降，甚至正常考ABR仍有改变。AP出现率随肿物增大而降低，－SP／AP比值≥0．4，可能是继发性伤及耳蜗所致。5例ABR表现正常者仍有半规管功能低下。提示前庭功能检查对桥小脑均占位性病变的诊断具有一定参考意义，临床应将ECochG和前庭功能检测列为诊断桥小脑角占位性病变的参考指标。     

中国西北地区线粒体DNA12SrRNAA1555G和GJB2基因突变

目的研究mtDNA 12SrRNA A1555G突变和GJB2突变在西北地区非综合征型感音神经性聋患者中的流行情况,探讨GJB2基因与mtDNA A1555G点突变的关系。方法收集本地区221例非综合征感音神经性聋患者的基因组DNA,多聚酶链反应扩增线粒体DNA和GJB2基因目的片断,Alw26Ⅰ限制性内切酶检测A1555G点突变,对酶切阳性病例和全部的GJB2基因的PCR产物进行DNA测序。结果21例患者检出mtDNA 12SrRNA A1555G突变;发现GJB2基因11种序列改变,有44例患者检出GJB2致病突变,235delC占携带致病突变患者的54．54％：在21例A1555G突变患者中,11例为GJB2基因多态改变,9例未检出GJB2基因序列改变,1例为109G→A（V371）突变。结论mDNA 12SrRNA A1555G在这一地区人群中有较高的发生频率．235delC是本地区GJB2基因突变的主要形式,GJB2基因突变不是mtDNA A1555G突变致聋的主要修饰因素。     

国人conneXin 2 6基因突变与先天性感音神经性耳聋的相关性研究

目的探讨国人耳聋人群中connexm26基因的突变频率和位点.方法收集15例有遗传性耳聋家族史的病例和252例散发性先天性耳聋病例血液样本,使用PCR-SSCP方法分析connexin26基因编码区突变.同时采用PSDM和BsBsiYI酶切的方法,直接检测异常connexin26基因35delG的突变.结果检出突变样本46例,其中散发耳聋患者中38例,突变率为15.1%;有家族史的聋儿15例中8例,突变率为53.3%.46例中5份有相似的异常电泳带,PCR产物直接测序,其形式为79位G→A的突变;另外在散发耳聋患者中还发现2例251delT和233delC,PDSM分析未发现有35delG的突变.结论国人先天性耳聋患者中存在着connexin26基因的高突变率,但突变热点与国外报道的不同,推测connexin26基因突变有明显的种族特异性.     

Cochlear implantation for children with GJB2-related deafness

OBJECTIVES/HYPOTHESIS: Mutations in GJB2 are a common cause of congenital sensorineural hearing loss. Many children with these mutations receive cochlear implants for auditory habilitation. The purpose of the study was to compare the speech perception performance of cochlear implant patients with GJB2-related deafness to patients without GJB2-related deafness. STUDY DESIGN: Retrospective case review. METHODS: Pediatric cochlear implant recipients who have been tested for GJB2 mutation underwent chart review. All patients received cochlear implantation at a tertiary referral center, followed by outpatient auditory habilitation. Charts were reviewed for cause and duration of deafness, age at time of cochlear implantation, intraoperative and postoperative complications, duration of use, and current age. Results of standard tests of speech perception administered as a part of the patients' auditory habilitation were reviewed. RESULTS: Twenty patients with GJB2 mutations were compared with 27 patients without GJB2 mutations. There was no statistical difference between patients with and without GJB2-related congenital sensorineural hearing loss with regard to open-set and closed-set speech recognition performance at 12, 24, and 36 months after cochlear implantation. Surgical complications were uncommon. CONCLUSION: Pediatric patients with congenital sensorineural hearing loss without other comorbid conditions (eg, developmental delay, inner ear malformations) perform well when they receive cochlear implantation and auditory habilitation. The presence or absence of GJB2 mutation does not appear to impact speech recognition performance at 12, 24, and 36 months after implantation.