Spectrum of GJB2 mutations causing deafness in the British Bangladeshi population

Objective: Mutations in Gap Junction Beta 2 (GJB2) (the gene encoding the protein Connexin 26) have been found to be a major cause of non‐syndromic sensorineural recessive deafness. The mutations in GJB2 causing hearing impairment vary in different populations. The aim of this study was to determine the prevalence and spectrum of GJB2 mutations in prelingual deafness in a population of Bangladeshi origin in the UK. Design: Cross‐sectional survey. Setting: Community based audiology clinic and tertiary level genetics department. Methods: Fifty‐three families (67 patients) with sensorineural hearing loss of unknown cause were included in the study. Detailed history and examination excluded syndromic and environmental causes of hearing loss in the subjects as far as possible. Genetic analysis was performed, specifically looking for mutations in the GJB2 gene. Results: Of the 53 families, 14 were confirmed to have biallelic pathogenic mutations in GJB2 (26%). The most common mutations of GJB2 in this population were W24X, IVS1+1, M1V, W77X and Q124X, W24X being the most common mutation seen in 57% of patients. Conclusion: Mutations in GJB2 are responsible for over one quarter of non‐syndromic sensorineural deafness in the British Bangladeshi population. It is recommended that all Bangladeshi patients with non‐syndromic hearing loss should be first tested for GJB2 mutations before requesting other aetiological investigations.     

Prevalence of 35de1G/GJB2 and del (GJB6-D13S1830) mutations in patients with non-syndromic deafness from a population of Espírito Santo - Brazil

Mutations in GJB2 gene are the leading cause of deafness in autosomal recessive inheritance, and the 35delG mutation is the most common in many ethnic groups. Besides the 35delG mutation in homozygosis, the mutation is also found in compound heterozygosis, coupled with other mutations in genes GJB2 and GJB6.AimTo determine the prevalence of 35delG/GJB2 and del (GJB6-D13S1830) mutations in patients with sensorineural hearing impairment in residents from the Espirito Santo state, Brazil.Materials and methods77 unrelated individuals with moderate to profound sensorineural hearing loss were evaluated. The 35delG mutation was studied by PCR / RFLP; and the del (GJB6-D13S1830) mutation was screened by the technique of multiplex PCR.Results88.3% had normal genotype for the studied mutations, 1.3% were compound heterozygotes, 3.9% homozygotic for the 35delG mutation, 6.5% heterozygotic for 35delG/GJB2. The frequency of 35delG/GJB2 and del (D13S1830/GJB6) alleles in the sample was 7.8% and 0.65%, respectively.ConclusionThe data confirmed the existence of the mutations studied in cases of sensorineural hearing loss in a population from Espírito Santo / Brazil. These findings reinforce the importance of genetic diagnosis, which can provide early treatment for children and genetic counseling for the affected families.     

A study of GJB2 and delGJB6-D13S1830 mutations in Brazilian non-syndromic deaf children from the Amazon region

Hearing impairment affects about 1 in 1000 newborns. Mutations in the connexin 26 (GJB2) gene rank among the most frequent causes of non-syndromic deafness in different populations, while delGJB6-D13S1830 mutation located in the DFNB30 locus is known to cause sensorineural hearing loss. Despite the many studies on the involvement of GJB2 mutations in hearing impairment in different populations, there is little information on genetic deafness in Brazil, especially in the Amazon region.ObjectiveTo determine the prevalence of GJB2 mutations and delGJB6-D13S1830 in 77 sporadic non-syndromic deaf patients.MethodThe coding region of the GJB2 gene was sequenced and polymerase chain reaction was performed to detect the delGJB6-D13S1830 mutation.ResultsMutant allele 35delG was found in 9% of the patients (7/77). Mutations M34T and V95M were detected in two distinct heterozygous patients. Non-pathogenic mutation V27I was detected in 28.6% of the patients (22/77). None of the deaf patients carried the delGJB6-D13S1830 mutation.ConclusionMutant alleles on gene GJB2 were observed in 40% (31/77) of the subjects in the sample. Pathogenic variants were detected in only 12% (9/77) of the individuals. More studies are required to elucidate the genetic causes of hearing loss in miscegenated populations.     

山西太原129例重度非综合征型感音神经性耳聋基因的筛查

目的应用耳聋基因芯片对重度极重度非综合征型感音神经性耳聋患者进行筛查。方法采集本地区聋哑学校和门诊散发的重度极重度非综合征型感音神经性耳聋患者129人的外周血并提取DNA,应用耳聋基因芯片检测GJB2,GJB3,SLC26A4,线粒体DNA(mitochondrial,mtDNA)12SrRNA热点突变位点。结果该耳聋人群中与筛查位点有关的耳聋比例占41.09%,共检出GJB2基因突变26例(20.16%);mtDNA突变8例(6.2%);SLC26A4基因突变21例(16.28%);未检出GJB3基因突变。结论本组耳聋人群中与筛查位点有关的耳聋比例高达41.09%,GJB2突变是该人群遗传性聋的最常见病因,SLC26A4突变为第二常见病因。     

耳聋基因相关感音神经性聋患儿临床特点分析

目的 探讨GJB2、SLC26A4基因突变相关感音神经性聋患儿的临床表现特点.方法 以经耳聋基因芯片及DNA测序确诊为GJB2、SLC26A4基因突变的0~12岁感音神经性聋患儿218例为研究对象,其中GJB2纯合或复合突变患者123例,SLC26A4纯合或复合突变患者95例.分析GJB2、SLC26A4基因突变患儿的发病年龄构成、听力损失程度及颞骨CT影像学特点.结果 ①发病年龄在婴儿期(0~1岁)、幼儿期(>1~3岁)、学龄前期(>3~6岁)、学龄期(>6~12岁)GJB2、SLC26A4基因突变患儿组的构成比分别为:43.09%、37.40%、14.63%、4.88%和24.2%、44.21%、18.95%、12.63%,两种基因突变组发病年龄构成比差异有统计学意义(P=0.014).②听力损失程度为中、重、极重度的GJB2、SLC26A4基因突变患儿构成比分别为:8.94%、17.89%、73.17%及9.47%、34.74%、55.79%,GJB2基因突变患儿中以极重度听力损失为主,与SLC26A4基因突变患儿听力损失程度构成比差异有统计学意义(P=0.014).③GJB2基因突变组中99.19%(122/123)患儿内耳结构正常,仅一例CT显示双侧内听道狭窄;SLC26A4基因突变组中有95.79%(91/95)患儿颞骨CT显示有前庭水管扩大.结论 本组GJB2基因突变感音神经性聋患儿发病年龄以婴儿期居多,以极重度感音神经性聋为主,多不伴内耳畸形;SLC26A4基因突变感音神经性聋患儿发病年龄以幼儿期居多,以重度、极重度感音神经性聋为主,与前庭水管扩大相关内耳畸形密切相关.     

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.     

散发感音神经性聋患者中GJB2基因突变检测的临床意义

目的探讨散发感音神经性聋患者中GJB2基因突变检测的临床指导意义.方法运用聚合酶链反应对解放军总医院听力诊断中心收集的242例散发感音神经性聋患者(135例语前聋患者,107例语后聋患者)的GJB2基因编码区进行扩增,扩增产物纯化后直接测序分析.结果 135例语前聋患者中GJB2基因致病突变的复合杂合和纯合个体有26例,占语前聋个体的19.26%;107例语后聋患者中未发现复合杂合和纯合致病突变,仅发现3例235delC杂合突变携带者、1例176del16杂合突变携带者.结论语前聋者GJB2基因致病突变阳性率明显高于语后聋患者,语前聋患者常规进行GJB2基因检测可从基因水平明确诊断,并为耳聋患者提供重要遗传信息.     

Sensorineural hearing loss in Jewish children born in Jerusalem

OBJECTIVE: Many factors, hereditary and environmental, may cause deafness. The aim of the present study was to analyze data on the etiology of bilateral sensorineural hearing impairment in children born in the Jerusalem area during 1978-1991, and to compare the results to those of a previous survey (1968-1977) in the same area. METHODS: The study included 150 Jewish children (139 families) with hearing loss, born during 1978-1991. Information was obtained on prenatal, perinatal and postnatal events, history of hearing loss in the family, the parents' communities and consanguinity. Children with a sensorineural hearing impairment of 56 dB HL or greater in the better ear, within the frequency range of 0.5-4 kHz were included in the study. The hearing loss was classified as moderate-severe (56-70 dB HL), severe (71-90 dB HL) and profound (91 dB HL or more) in the better ear. Mutations in the coding sequence of the connexin 26 (C x 26) and the connexin 30 genes were examined in some of the families. RESULTS: The hearing impairment was hereditary in 66 (44%) of the children, environmental in 31 (21%) and four children (3%) had multiple malformations. The cause was unknown in 49 (33%) children. Sixty-two families were of European origin (Ashkenazim) and 62 of Afro-Asian origin (Sephardim). Consanguinity was in 7% of the families. Mutations in connexin 26 and the deletion in connexin 30 were diagnosed in 9/18 families tested. The incidence of hearing loss decreased from 1.28 per thousand during 1968-1977 to 1.06 per thousand during 1978-1991. The rate of environmental causes decreased over the years together with an increase in the rate of unknown causes. The rate of hearing loss among Sephardim decreased significantly and increased among Ashkenazim. CONCLUSIONS: The rate of hearing impairment in Israel is as that found in other countries, as was the distribution of the causes of deafness. The decrease in the rates of hearing impairment among the Sephardim may be due to a continuing decrease in consanguineous marriages among Sephardim. It is expected that the group of unknown causes will become smaller in future with the availability of more molecular genetic tests.     

Decline in the prevalence of childhood deafness in the Jewish population of Jerusalem: ethnic and genetic aspects

A longitudinal study was performed on 147 Jewish children with bilaterally sensorineural hearing loss of moderately severe to profound degree, born in Jerusalem during the eighteen years 1968-85. The prevalence rate of these children declined during the years 1977-85, and at the same time the rate of consanguinity of their parents decreased; this decline was more evident in the genetic group among children with non-Ashkenazi ethnic origin. No such decline was found among the Ashkenazi children and no consanguinity among parents of these children was recorded. Our study supports the assumption that restriction of consanguineous matings may affect the prevalence of genetic deafness in children in a well-defined population. We have tried to remain unbiased and concede certain shortcomings in our present study.     

Clinical course of hearing and language development in GJB2 and non-GJB2 deafness following habilitation with hearing aids

Mutations in the GJB2 gene (connexin 26) are the most common cause of nonsyndromic autosomal recessive sensorineural hearing loss. Genetic testing of GJB2 may offer opportunities to predict the features of hearing loss and prognostication of speech-language development in children with hearing loss. The present study assessed the clinical features of hearing and some aspects of language development in congenital deafness due either to GJB2 mutations or to other factors in Japanese patients who had been habilitated with hearing aids. Thirty-five unrelated subjects with nonsyndromic, congenital, bilateral sensorineural hearing loss were enrolled in the study. Among them, 16 had biallelic GJB2 mutations related to hearing loss and 17 lacked such mutations. As has been reported in populations of European ancestry, the present Japanese subjects with GJB2 mutations had a relatively high incidence of the flat pattern audiogram and nonprogressive pure tone thresholds compared with subjects without GJB2 mutations. Subjects with GJB2 mutations and those without GJB2 mutations both showed a similar tendency in speech perception, some aspects of language development, and communication methods. In both groups, development of reading ability tended to be normal, but vocabulary development tended to be delayed. The present results establish the basis for future studies to aid in the evaluation and follow-up of patients with congenital hearing loss associated with GJB2 mutations who are habilitated with hearing aids.     

130例婴幼儿听力损失的听力学和基因学分析

目的 探讨0～3岁听障婴幼儿的基因学致聋因素,分析基因与环境致聋因素的相关性.方法 对130例听障患儿进行了客观听力学评估,并进行线粒体DNA(mtDNA)12SrRNA、GJB2基因、SLC26A4基因检测.84例患儿完成了影像学评估.结果 130例患儿中,前庭水管扩大综合征54例,听神经病7例.有明确高危因素患儿85例,占65.4%(85/130);23例有耳毒性药物用药史,其中以庆大霉素居多;13例有家族史,2例家族中存在近亲结婚.基因检测结果 显示130例患儿中,42例检测到SLC26A4基因致病突变,占32.3%(42/130);6例患儿检测到GJB2基因致病突变,占4.6%(6/130);130例患儿中未检测到mtDNA 12S rRNA C1494T以及A1555G突变.结论 在0～3岁的婴幼儿听力筛查诊断中,36.9%的听障患儿为遗传因素致聋.早期进行听力诊断联合分子诊断可提早发现病因,有利于随后的干预和康复治疗,同时也有利于进行有效的遗传咨询.     

Screening for monogenetic del(GJB6-D13S1830) and digenic del(GJB6-D13S1830)/GJB2 patterns of inheritance in deaf individuals from Eastern Austria

Genetically caused congenital deafness is a common trait affecting 1 in 2000 newborn children and is predominantly inherited in an autosomal recessive fashion. Genes such as the gap junction protein beta 2 (GJB2) encoding for Connexin (Cx26) and GJB6 (Cx30) are known to cause sensorineural deafness. Autosomal recessive deafness has been linked both to the monogenetic occurrence of mutated GJB2 or the GJB6 deletion del(GJB6-D13S1830) and digenic GJB2/del(GJB6-D13S1830) inheritance. Monogenetic GJB2 alterations are responsible for 25.5% of deafness in the eastern Austrian population. An additional 9.8% are heterozygous carriers of a single GJB2 mutation which is not responsible for deafness alone. Del(GJB6-D13S1830) and GJB2/del(GJB6-D13S1830) mutations have been shown to be the second most frequent cause of deafness in different populations. To address the question of the relevance of mutations in GJB6 either as a monogenetic or a digenic GJB2/del(GJB6-D13S1830) cause of deafness in this population, 76 unrelated individuals (33 families and 43 sporadic cases) were screened using PCR strategies. Similar to studies in other hard of hearing populations with similar or lower carrier frequencies of single GJB2 mutations, the presence of del(GJB6-D13S1830) was not detected in any individual within the patient group. Data therefore exclude a digenetic association of del(GJB6-D13S1830) with heterozygous GJB2 mutations as a cause of deafness in a representative sample of the population from Eastern Austria.     

Late postnatal onset of hearing loss due to GJB2 mutations

GJB2 mutations account for approximately 50% of recessive non-syndromic deafness, with 35delG being the most prevalent. Homozygous 35delG mutations cause pre-lingual, non-progressive hearing loss that is detected on newborn hearing screening programmes. We present a sibling pair with homozygous 35delG mutations, who passed hearing tests in early infancy and developed progressive sensorineural hearing loss, one requiring a cochlear implant. These cases illustrate that deafness due to such mutations may have a late onset and consequently be missed on neonatal screening programmes and they may present an argument to consider neonatal screening for GJB2 mutations in order to aid early intervention.     

Audiological profile of the prevalent genetic form of childhood sensorineural hearing loss due to GJB2 mutations in northern Greece

The present study describes the audiological profile of genetic hearing loss resulting from GJB2 mutations in northern Greece, as this represents the most frequent single cause of childhood sensorineural hearing loss. The 35delG mutation in homozygosity was detected in 27 of 107 patients (25.2%). The audiological profile is that of a profound or severe sensorineural hearing loss, with a sloping or flat configuration of the audiogram, mostly symmetrical, non-progressive and affecting more the higher frequencies. This profile underlines the importance of early identification and genetic family counseling leading to the future possibility of prevention of deafness.     

Prevalence of GBJ2 mutations in patients with severe to profound congenital nonsyndromic sensorineural hearing loss in Bulgarian population

Objective of the study is to assess the prevalence of Connexin 26 (GJB2) mutation in patients with congenital nonsyndromic sensorineural hearing loss in Bulgarian population. Study design is done prospectively. Patient inclusion criteria for this study were diagnosis of congenital nonsyndromic hearing loss, and absence of potential sibling relationships between patients included in the study (anamnestic pedigree for at least three generations). Patients were excluded from the study group if one of the following conditions were present: secondary hearing loss (cytomegalovirus, rubella, meningo-encephalitis, mastoiditis, other infections, posterior fossa tumors, etc.), exposure to drugs or other prenatal or perinatal etiology of deafness, and congenital syndromic hearing loss. Genomic DNA samples from whole blood were tested with sequence analysis for mutations in the coding region of the GJB2. Results state that 51 patients were analyzed for GJB2 mutations. Twenty of the patients (39%) with mutant alleles were homozygous for the c.35delG mutation (c.35delG/c.35delG) and four patients (8%) presented as heterozygotes (c.35delG/WT). In one patient, who carried a heterozygous mutation c.35delG, a second mutation was found—312del114. Additionally, in two other patients were discovered the mutations Trp24X (W24X) and, respectively, Arg127His(R127H), both in heterozygous states. From the whole study group there was only one patient with compound heterozygous genotype—p.Leu90Pro(L90P)/p.Ile121Asn. The latter one has never been reported in the literature so far. In conclusion, this study determines the importance of connexin 26 mutations in Bulgarian children with severe to profound congenital nonsyndromic sensorineural hearing loss, the prevalence of the different mutation variants and their relationship with the ethnical background of the patients. In addition, we report for the first time a novel mutation in the GJB2 gene.     

湖北地区306例极重度聋患儿基因芯片筛查分析

目的：通过检测湖北地区极重度感音神经性聋患儿常见耳聋基因突变情况,分析该人群的分子病因学特点,为临床耳聋防治和遗传咨询提供参考。方法：收集306例湖北地区极重度感音神经性聋患儿,抽取外周血,提取DNA,应用遗传性耳聋基因芯片检测GJB2、GJB3、SLC26A4和线粒体12SrRNA4个基因的9个突变热点。对所有携带SLC26A4基因突变患者进行颞骨CT扫描。结果：306名患儿中,132例（43．14％）检出携带不同基因突变,其中有2例携带双基因突变。GJB2基因突变检出率为29．41％（90／306）,SLC26A4基因突变检出率为13．72％（42／306）,线粒体12SrRNA基因突变检出率为O．65％（2／306）。本组患者未检出GJB3基因突变。36例携带SLC26A4基因突变者颞骨CT扫描显示前庭水管扩大。结论：GJB2基因和SLC26A4基因是本组患儿最主要的致聋基因,其中235delC突变为最常见的突变位点,其次为1VS7—2A〉G突变。筛查SLC26A4基因常见突变有助于大前庭水管综合征的诊断。     

The novel c.247_249delTTC (p.F83del) GJB2 mutation in a family with prelingual sensorineural deafness

Non-syndromic hearing loss is one of the most common hereditary determined diseases in human, and the disease is a genetically heterogeneous disorder. Mutations in the GJB2 gene, encoding connexin 26 (Cx26), are a major cause of non-syndromic recessive hearing impairment in many countries and are largely dependent on ethnic groups. Due to the high frequency of the c.35delG GJB2 mutation in the Greek population, we have previously suggested that Greek patients with sensorineural, non-syndromic deafness should be tested for the c.35delG mutation and the coding region of the GJB2 gene should be sequenced in c.35delG heterozygotes. Here we present on the clinical and molecular genetic evaluation of a family suffering from prelingual, sensorineural, non-syndromic deafness. A novel c.247_249delTTC (p.F83del) GJB2 mutation was detected in compound heterozygosity with the c.35delG GJB2 mutation in the proband and was later confirmed in the father, while the mother was homozygous for the c.35delG GJB2 mutation. We conclude that compound heterozygosity of the novel c.247_249delTTC (p.F83del) and the c.35delG mutations in the GJB2 gene was the cause of deafness in the proband and his father.     

Sudden hearing loss in a family with GJB2 related progressive deafness

Mutations of GJB2, the gene encoding connexin 26, have been associated with prelingual, sensorineural hearing loss of mild to profound severity. One specific mutation, the 35delG, has accounted for the majority of mutations detected in the GJB2 gene in Caucasian populations. Recent studies have described progression of hearing loss in a proportion of cases with GJB2 deafness. We report an unusual family with four 35delG homozygous members, in which the parents were deaf-mute whilst both children had a postlingual progressive hearing loss. Furthermore, the son suffered from sudden hearing loss.     

Correlation between GJB2 mutations and audiological deficits: personal experience

Mutations in GJB2 gene are the most common cause of genetic deafness. More than 100 mutations have been described. The aim of this work is to describe the personal experience in genetic hearing loss, investigating the audiological and genetical characteristics of Cx26 deafness and correlating genotype and phenotype. We performed audiological and genetical evaluation in 154 patients affected by non-syndromic deafness of different degree. All patients showed a bilateral symmetrical sensorineural hearing loss. From the genetical analysis 127 probands resulted as negatives while 27 as positives (51.8% homozygous for 35 delG, 14.8% compound heterozygosis and 33.3% single mutation); 7.5% of patients had a mild deafness, 37% moderate, 33.3% severe and 22.2% profound. The c.35 delG mutation was detected in 66.6% of patients. Three mutations were found in compound heterozygosis with 35 delG, six different single mutations already described, and a new mutation S138G were also found. Correlation between genotype and phenotype confirmed the high variability of hearing loss.     

Lyme borreliosis, an etiological factor in sensorineural hearing loss?

The incidence of Lyme borreliosis was studied prospectively in 165 patients with acute idiopathic sensorineural hearing loss. The prevalence of positive levels of antibodies against Borrelia burgdorferi was sixfold higher in patients with sensorineural hearing loss than in the general population in Finland. Four patients fulfilled the criteria for Lyme borreliosis. No specific risk factors were found with which to predict the occurrence of Lyme borreliosis among patients with hearing loss. In logistic regression modeling the poor outcome of hearing loss was best explained by advanced age, high-frequency or flat-type hearing loss, and absence of positive levels of antibodies against B. burgdorferi. Although the causal relationship between Lyme borreliosis and sensorineural hearing loss is difficult to verify, we suggest that Lyme borreliosis is a rare but potentially treatable cause of sudden deafness. We propose that in endemic areas antibodies against Lyme borreliosis should be determined in patients with idiopathic sensorineural hearing loss. Received: 22 March 1999 / Accepted: 14 September 1999