Connexin 26 and connexin 30 mutations in children with nonsyndromic hearing loss

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.     

新疆哈萨克族非综合征型聋GJB2基因突变的研究分析

目的：研究新疆哈萨克族非综合征型聋患者GJB2基因突变的情况。方法：调查对象为来自新疆地区的193例哈萨克族患者,采用直接测序法对非综合征型聋患者97例和健康对照96例进行GJB2基因突变的检测。结果：在编码区耳聋组共发现8种碱基改变：其中35delG纯和12例,79G〉A纯合5例,79G〉A杂合8例,79G〉A与608T〉C复合杂合1例,79G〉A与341A〉G复合杂合5例,235delC杂合4例,341A〉G杂合2例,439T〉G杂合1例,457G〉A杂合1例,521G〉A纯合2例。对照组发现4种已明确的常见多态性碱基改变。结论：本研究提示新疆哈萨克族非综合征型聋患者GJB2基因突变具有种族和地域性特点,该地区哈萨克族耳聋人群中GJB2有较高携带率,在本研究中35 delG为其常见突变方式。     

Spectrum and frequency of GJB2 mutations in a cohort of 264 Portuguese nonsyndromic sensorineural hearing loss patients

Abstract

Objective: To assess the spectrum and prevalence of mutations in the GJB2 gene in Portuguese nonsyndromic sensorineural hearing loss (NSSHL) patients. Design: Sequencing of the coding region, basal promoter, exon 1, and donor splice site of the GJB2 gene; screening for the presence of the two common GJB6 deletions. Study sample: A cohort of 264 Portuguese NSSHL patients. Results: At least one out of 21 different GJB2 variants was identified in 80 (30.2%) of the 264 patients analysed. Two mutant alleles were found in 53 (20%) of these probands, of which 83% (44/53) harboured at least one c.35delG allele. Twenty-seven (10.2%) of the probands harboured only one mutant allele. Subsequent analysis revealed that the GJB6 deletion del(GJB6-D13S1854) was present in at least 7.4% (2/27) of the patients carrying only one mutant GJB2 allele. Overall, one in five (55/264) of the patients were diagnosed as having DFNB1-related NSSHL, of which the vast majority (53/55) harboured only GJB2 mutations. Conclusions: This study provides clear demonstration that mutations in the GJB2 gene are an important cause of NSSHL in Portugal, thus representing a valuable indicator as regards therapeutical and rehabilitation options, as well as genetic counseling of these patients and their families.     

GJB2 mutations in hearing impairment: identification of a broad clinical spectrum for improved genetic counseling

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.     

A novel missense mutation in the Connexin 26 gene associated with autosomal recessive nonsyndromic sensorineural hearing loss in a consanguineous Tunisian family

Nonsyndromic sensorineural hearing impairment is inherited in a predominantly autosomal recessive manner in up to 70% of cases. The gene more often involved is GJB2, encoding the gap junction protein Connexin 26. We report here a novel missense mutation in the GJB2 gene found in a Tunisian family. A homozygous change C/G at nucleotide 263 was detected in the 4-year-old girl of this family, affected by congenital moderate hearing loss. This transversion leads to the replacement of a highly conserved alanine with glycine at codon 88 (A88G). The consanguineous parents of the child are healthy carriers of the mutation.     

Spectrum and frequency of GJB2 mutations causing deafness in the northwest of Iran

Objective

Mutations in GJB2 and GJB6 which comprise DFNB1 locus cause up to half of all cases of the prelingual autosomal recessive non-syndromic hearing loss (ARNSHL) worldwide. This study has intended to assess the spectrum and frequency of GJB2/GJB6 mutations in northwest of Iran.

Methods

508 Patients with presumed ARNSHL were analyzed by applying ARMS-PCR, SSCP, PCR-RFLP and sequencing assays.

Results

Seventy-five (14.7%) different homozygous and eighty-seven (17.1%) different compound heterozygous genotypes were detected in this cohort. Concerning the GJB2 gene, c.35delG was the most prevalent mutation, accounting for 16.4% of the samples. In addition 29 sequence variations other than c.35delG mutation were distinguished in GJB2; namely, delE120, Ins A 290-291, R143Q, V37I, R32H, Y155X, V27I + T123N, F154F, 167delT, 312del14, 299-300delA, T8M, W24X, E114G + V27I, 235delC, R184P, V153I, S139N, A171T, M163V (unknown mutation), G127V, E147X, R127H, 35insG, R143W, V27I, G160S, E114G and IVS1 + 1G > A. Moreover, the IVS1 + 1G > A was accounted as a second common mutation.

Conclusions

Overall, the frequency of GJB2 mutations (≥31%) is in agreement with other white population. These findings highlight the importance of the study of GJB2 gene in the diagnosis to provide early treatment and genetic counseling.     

Prevalence of the c.35delG and p.W24X mutations in the GJB2 gene in patients with nonsyndromic hearing loss from North-West Romania

Objective

In Central and South-Eastern European countries, the most frequent mutation types responsible for congenital nonsyndromic sensorineural hearing loss (NSHL) are c.35delG and p.W24X (15-55.8% and 2.5-4.3%, respectively). The aim of the study was to determine for the first time in Romania the prevalence of c.35delG and p.W24X mutations in patients with NSHL.

Material

75 unrelated children with NSHL from Transylvania (North-West Romania).

Methods

a. Audiological examination (otoscopy, tympanogram, acoustic otoemission and tonal audiogram or auditory evoked potentials); b. detection of the c.35delG (semi-nested-PCR, RFLP and ARMS-PCR analysis) and p.W24X (ARMS-PCR analysis) mutations.

Results

Audiological examination allowed the diagnosis of hearing loss of various degrees: moderate in 8 patients (10.7%), severe in 14 cases (18.7%), profound in 53 patients (70.6%). The number of reported mutation cases as against the number of alleles indicates a 33.3% frequency rate for c.35delG mutation and respectively 5.3% for p.W24X mutation. All 22 patients with 35delG/c.35delG genotype (19 patients), c.35delG/p.W24X genotype (2 patients) or p.W24X/p.W24X genotype (1 patient) presented profound/severe hearing loss.

Conclusion

Our study confirms that the frequency rate of the two mutations analyzed in patients with NSHL from North-West Romania is comparable to that seen in other Central and South-Eastern European countries. The homozygote or compound heterozygote states represent a major risk factor for profound or severe deafness. Audiological screening in newborns and genetic testing in confirmed congenital hypoacusis cases are compulsory for early therapeutic intervention (hearing prosthesis or cochlear implant) and genetic counselling.     

Prevalence of c.35delG and p.M34T mutations in the GJB2 gene in Estonia

Objective

The purpose of this study was to determine the prevalence of c.35delG and p.M34T mutations in the GJB2 gene among children with early onset hearing loss and within a general population of Estonia.

Methods

Using an arrayed primer extension assay, we screened 233 probands with early childhood onset hearing loss for 107 different mutations in the GJB2 gene. We then looked for the two most common mutations, c.35delG and p.M34T, in a population of 998 consecutively born Estonian neonates to determine the frequency of these mutations in the general population.

Results

In 115 (49%) of the patients with early onset hearing loss, we found a mutation in at least one allele of the GJB2 gene. Seventy-three (31%) were homozygous for the c.35delG mutation, seven (3%) were homozygous for the p.M34T mutation, and five (2%) had c35delG/p.M34T compound heterozygosity. Other six identified mutations in GJB2 gene occurred rarely. Among the 998 anonymous newborn samples, we detected 45 who were heterozygous for c.35delG, 2 individuals homozygous for c.35delG, and 58 who were heterozygous for p.M34T. Additionally, we detected two c.35delG/p.M34T compound heterozygotes.

Conclusion

The most common GJB2 gene mutations in Estonian children with early onset hearing loss were c.35delG and p.M34T, with c.35delG accounting for 75% of GJB2 alleles. The carrier frequency for c.35delG and p.M34T in a general population of Estonia was 1 in 22 and 1 in 17, respectively, and was higher than in most other countries.     

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.     

The effect of GJB2 allele variants on performance after cochlear implantation

OBJECTIVES/HYPOTHESIS: It has been hypothesized that etiology of hearing loss may serve as an independent variable in performance after cochlear implantation. To test this hypothesis, the authors identified pediatric cochlear implant recipients with gap junction protein beta2 (GJB2)-related deafness. The study examines performance outcomes associated with GJB2 deafness-causing allele variants. STUDY DESIGN: Pediatric cochlear implant patients were screened for GJB2 allele variants; statistical comparisons were made with prospectively obtained performance measures. METHODS: From 181 children who participated in a nationwide cochlear implant research program, 122 children were identified with congenital nonsyndromic sensorineural hearing loss and invited to participate. Screening for GJB2 allele variants was completed for 55 children. The children were homogeneous with respect to age (8 or 9 y) and age at implant (before age 5 y). All patients have previously undergone a prospective regimented battery of performance measures. RESULTS: Performance measures were compared between 22 children with and 33 children without mutations to determine whether GJB2 status was a significant predictor of cochlear implant outcomes. Reading and cognitive outcomes were significantly dependent on connexin status. The group of children who tested positive for GJB2-related deafness scored significantly higher on a nonverbal cognitive measure, Block Design, and on a measure of reading comprehension. CONCLUSION: The isolated insult to the cochlea created by GJB2 allele variants allows for preservation of central cognitive function. Better reading performance is seen in children with GJB2-related deafness.     

柳州市盲聋学校非综合征性聋分子病因学分析--GJB2 235delC突变和线粒体DNA 12SrRNA A1555G突变筛查报告

目的 分析GJB2 235delC突变和线粒体DNA 12SrRNA A1555G突变在广西壮族自治区柳州地区非综合征性耳聋（nonsyndromic hearing impairment，NSHI）患儿中的作用。方法 收集广西壮族自治区柳州聋哑学校的88例非综合征性耳聋患儿的血样，提取DNA后经聚合酶链反应（PCR）分别扩增GJB2基因编码区及线粒体DNA，ApaI酶切分析GJB2 235位点的C缺失突变、Prey—DAF药物性耳聋基因诊断试剂盒分析线粒体1555位点的A—G突变，对GJB2 235delC及线粒体DNA 12SrRNA A1555G的突变率进行统计分析。结果 88例患儿中1例（1．14％）为GJB2 235delC纯合突变；5例（5．68％）为GJB2 235delC杂合突变；4例（4．55％）存在线粒体DNA 12SrRNA A1555G点突变，其中1例同时伴有GJB2 235delC杂合突变。在分子水平能够明确诊断者占11．37％。结论 柳州地区耳聋患者常染色体隐性遗传性耳聋发生率较全国平均水平低，线粒体DNA 12SrRNA A1555G突变发生率偏高。应用基因诊断技术可以在地区性耳聋病因调查中进行快速筛查、诊断，可达到防止聋儿再生、指导聋儿康复等积极效果。     

GJB2及SLC26A4基因突变患儿耳蜗植入效果分析

目的探讨GJB2及SLC26A4基因突变的患儿人工耳蜗植入(cochlear implantation,CI)术后的效果。方法根据耳聋基因检测结果,将40名单侧CI患儿分成3组:GJB2组包括15名GJB2基因突变患儿,SLC26A4组包括8名SLC26A4基因突变患儿,对照组组包括17名未发现GJB2、SLC26A4及线粒体基因突变患儿。术后效果采用听觉意义整合量表(Meaningful Auditory Integration Scale,MAIS)、听觉行为分级标准(Categories of Auditory Performance,CAP)、规范学语时期出现时间、言语可懂度分级标准(Speech Intelligibility Rating,SIR)进行评估,比较3组术后1年效果差异的统计学意义。结果 GJB2基因突变组在MAIS及CAP两项评估中均明显优于其他两组,其差异有统计学意义。GJB2组的规范学语出现时间及SIR相较于另外两组也具有一定优势,但差异无统计学意义。SLC26A4组略优于非基因突变组,尽管统计学分析显示各项评估结果无显著差异。结论因病变部位在耳蜗,GJB2相关性耳聋患儿人工耳蜗植入术后效果较好,SLC26A4相关性耳聋术后是否存在优势有待进一步证实。     

武汉地区非综合征性聋分子病因学分析--GJB2 235delC突变和线粒体DNA 12SrRNA A1555G突变筛查报告

目的 分析武汉地区非综合征性耳聋（nonsyndromic hearing impairment，NSHI）患儿GJB2 235delC突变率和线粒体DNA A1555G突变率。方法 收集武汉市艺萌听力康复中心的94例耳聋患儿血样，非综合征性耳聋患儿88例，提取DNA后经聚合酶链反应（PCR）分别扩增GJB2基因编码区及线粒体DNA，ApaI酶切分析GJB2 235位点的C缺失突变，Prev—DAF药物性耳聋基因诊断试剂盒分析线粒体1555位点的A—G突变，对GJB2 235ddC及线粒体DNA A1555G的突变率进行统计分析。结果 88例患儿中9例（10．23％）为GJB2 235delC纯合突变，7例（7．96％）为GJB2 235delC杂合突变；2例（2．27％）存在线粒体DNA A1555G点突变。在分子水平能够明确诊断者占20．46％。结论 武汉地区耳聋患者存在较高的遗传性耳聋发生率，应用基因诊断技术可以在耳聋患者病因调查中进行快速诊断筛查，达到防止再生育聋儿、指导聋儿康复等积极效果。     

Childhood hearing impairment in northern Finland,etiology and additional disabilities

ObjectivesThe purpose of this study was to determine the prevalence and etiology of hearing impairment (HI) in Finnish children and to evaluate the frequency and type of additional disabilities among children with HI.MethodsSubjects consisted of 214 children with mild to profound HI ascertained until the age of 10 years. They belonged to the birth cohort spanning the years 1993–2002 in northern Finland. The clinical data were collected from the electronic patient records of the Oulu University Hospital. Age at ascertainment, degree and type of HI and audiogram configuration were determined. Risk factors and etiology of HI and co-existing disabilities were recorded.ResultsThe prevalence of childhood HI was 2.3/1000 live births (95% CI; 2.0, 2.7). The etiology of HI was genetic in 47.2%, acquired in 16.4% and unknown in 36.4% children. Among the 214 children with HI, 101 (47.2%) had other minor or major disabilities. The frequency of additional disabilities did not differ between children with mild HI and those with moderate or severe HI (p = 0.78). Additional disabilities were more common (65.7%) in children with acquired HI than in children with genetic or unknown HI (43.6%) (p = 0.035).ConclusionThe prevalence of childhood HI has remained unchanged in northern Finland as compared to previous studies. Genetic causes were the most common (47%) etiology of childhood HI. Among acquired causes of HI, perinatal risk factors were more common than previously. The frequency of additional disabilities was similar among children with different degrees of HI. Because almost 40% of children had one or more additional disabilities affecting development or learning, it is important to take them into consideration in rehabilitation.     

Common mutation analysis of GJB2 and GJB6 genes in affected families with autosomal recessive non-syndromic hearing loss from Iran: simultaneous detection of two common mutations (35delG/del(GJB6-D13S1830)) in the DFNB1-related deafness

OBJECTIVE: DFNB1 locus has been reported as a major cause of autosomal recessive non-syndromic hearing loss (ARNSHL) worldwide. 35delG and del(GJB6-D13S1830) are thought to be two common mutations in this locus among Caucasians. The aim of this study is to determine the significance of these two mutations in aetiology of ARNSHL in Iran. METHODS: One hundred and thirty-three unrelated patients with ARNSHL were tested by using multiplex allele-specific PCR assay after validation by positive control samples. RESULTS: The frequency of 35delG was about 18.5%, however, del(GJB6-D13S1830) was not found in the studied patients. Parental consanguinity was observed in 50% of 35delG-mutated families. CONCLUSIONS: Our results support founder effect regarding these mutations.     

A systematic review and meta-analysis of common mutations of SLC26A4 gene in Asian populations

Objectives

The IVS7-2A>G (c.919-2A>G) and p.H723R (c.2168A>G) mutations of SLC26A4 gene are recognized as a risk factor for the non-syndromic hearing loss. To elucidate the variable results, a meta-analysis and systematic review was performed from all case–control studies by pooling data on them.

Methods

The case–control studies were assessed with a modification of the Newcastle-Ottawa Scale (NOS). The strength of association between c.919-2A>G, c.2168A>G and hearing loss risk was measured by odds ratios (ORs) with 95% confidence intervals (CIs).

Results

We included 14 case–control studies and 16 case series studies in present study. There was a higher prevalence of the c.919-2A>G mutation in the case group than that in the control group (12.4% vs 0.9%; OR = 13.05, 95% CI: 8.41–20.23, Z = 11.47, P < 0.00001).

Conclusions

In conclusion, the results from this meta-analysis suggest that NSHL patients have an increased risk of the c.919-2A>G mutation of SLC26A4 gene in Asians, especially in Chinese.