Compound heterozygosity for dominant and recessive GJB2 mutations in a Tunisian family and association with successful cochlear implant outcome

Objectives

Mutations of GJB2 encoding connexin 26 are the most common cause of hearing loss. They are responsible for up to 50% of ARNSHL. The pathogenic mutations in this gene are generally inherited recessively. Dominant mutations in GJB2 also cause hearing loss, either in isolated non-syndromic form or as part of a syndrome associated with various skin disorders.

Methods

We screened a Tunisian child affected by congenital, bilateral, profound, sensorineural hearing loss for mutations in GJB2 gene using PCR and direct sequencing.

Results

The proband was found to be compound heterozygous for recessive and dominant GJB2 mutations respectively p.V37I (c.109G > A) and p.R143Q (c.428G > A). Surprisingly the hearing mother is a carrier for this dominant GJB2 mutation. This proband underwent a cochlear implant at four years old. The evaluation using APCEI and IT-MAIS tests at six months post implantation indicates a successful cochlear implant outcome since the deaf child began to acquire language abilities and auditory sensation.

Conclusions

The p.R143Q mutation was described for the first time in Tunisia. We confirm the low penetrance of this mutation since the proband mother is a carrier despite her normal hearing. We show the effectiveness of cochlear implant to restore the communication abilities and auditory sensation for our patient.     

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.     

Hearing loss associated with an unusual mutation combination in the gap junction beta 2 (GJB2) gene in a Chinese family

Objective

To assess the molecular etiology of nonsyndromic sensorineural hearing loss (NSHL) in members of an affected Chinese family.

Methods

Common hearing-related genes including gap junction beta 2 (GJB2), SLC26A4, mitochondrial DNA 12S rRNA, GJB3 and GJB6 were examined in a family consisting of a normal hearing father, an NSHL-affected mother, one normal-hearing child and three NSHL-affected children. Specific primers were used in polymerase chain reactions to amplify the coding regions of the above genes from the peripheral blood DNA from each family member, and the genes were analyzed by direct sequencing. The subjects were evaluated for phenotypic characterization using audiometric testing and radiological examination of the inner ear.

Results

Pathogenic mutations in the GJB2 gene were identified. The affected mother showed a heterozygous G → A transition at nucleotide 232, resulting in an alanine to threonine substitution at codon 78 (p.A78T), and the normal hearing father had a c.35insG insertion mutation. The three affected children displayed heterozygosity for the GJB2 mutations, showing a previously unreported combination of c.35insG and c.232G>A.

Conclusions

The GJB2 mutations account for a significant proportion of NSHL in affected individuals worldwide. Genetic and audiological data analysis of a Chinese family with NSHL revealed a novel c.35insG/c.232G>A compound heterozygous state. Our results highlight the complexity of the GJB2 genotypes and phenotypes.     

Identification of both MT-RNR1 m.1555A>G and bi-allelic GJB2 mutations in probands with non-syndromic hearing loss

Objectives

Mutations in GJB2 and MT-RNR1 are common causes for non-syndromic sensorineural hearing loss (NSHL). In this study, we investigated the co-existence of both MT-RNR1 and bi-allelic GJB2 mutations in a large number of simplex and multiplex probands with NSHL.

Methods

485 simplex and 134 multiplex probands with NSHL were recruited for mutation screening of GJB2 and MT-RNR1 by bidirectional sequencing. Clinical features of probands with both MT-RNR1 and bi-allelic GJB2 mutations were further analyzed in comparison with extended family members.

Results

MT-RNR1m.1555A>G and bi-allelic GJB2 mutations were both detected in one (0.21%) simplex probands and two (1.49%) multiplex probands. Variable hearing phenotypes were found in a pair of siblings with both MT-RNR1 and bi-allelic GJB2 mutations.

Conclusion

MT-RNR1 and bi-allelic GJB2 mutations may co-exist not only in multiplex probands but also in simplex probands. The variable hearing phenotypes in closely-related family members may reflect the co-existence of different molecular causes and prompt extended genetic tests.     

Absence of GJB2 gene mutations, the GJB6 deletion (GJB6-D13S1830) and four common mitochondrial mutations in nonsyndromic genetic hearing loss in a South African population

Objective

The purpose of this study was to determine the prevalence of mutations in the GJB2 gene, the GJB6-D13S1830 deletion and the four common mitochondrial mutations (A1555G, A3243G, A7511C and A7445G) in a South African population.

Methods

Using single-strand conformation polymorphism and direct sequencing for screening GJB2 mutation; Multiplex PCR Amplification for GJB6-D13S1830 deletion and Restriction Fragment-Length Polymorphism (PCR-RFLP) analysis for the four common mtDNA mutations. We screened 182 hearing impaired students to determine the frequency of these mutations in the population.

Results

None of the reported disease causing mutations in GJB2 nor any novel pathogenic mutations in the coding region were detected, in contrast to the findings among Caucasians. The GJB6-D13S1830 deletion and the mitochondrial mutations were not observed in this group.

Conclusion

These results suggest that GJB2 may not be a significant deafness gene among sub-Saharan Africans, pointing to other unidentified genes as responsible for nonsyndromic hearing loss in these populations.     

Particular distribution of the GJB2/GJB6 gene mutations in Mexican population with hearing impairment

Background

Hereditary sensorineural hearing loss (SNHL) is a genetically heterogeneous disorder worldwide. Mutations in the GJB2 gene are a frequent cause of hereditary SNHL. There is a prevalence of certain mutations in various populations which suggests that specific mutations may be influenced by ethnic background.

Objective

To analyze the prevalence of GJB2, GJB6 mutations in several geographic areas of Mexico in patients with hereditary SNHL.

Materials and methods

One hundred and forty Mexican unrelated propositi with prelingual SNHL were included in the study. All patients had three previous generations born in Mexico and belonged to no specific ethnic group. Analyses of the GJB2 and GJB6 genes and mt.1555A < G were performed in all subjects.

Results

Twenty-three homozygous mutations, 57 heterozygous mutations, 1 double heterozygous (GJB2/GJB6) and 59 wild-type genotypes in the GJB2 gene were observed. Three patients had the homozygous c.del35 mutation whereas 26 patients were heterozygous for this gene defect. Only one patient with the GJB6 gene deletion was present (it includes the double heterozygous GJB2/GJB6). The mt.1555A > G mutation was not detected.

Conclusion

We found a great variety of mutations depending on the analyzed region in patients with SNHL; 57.86% of patients had affection in one or two alleles in GJB2 or GJB6 genes whereas 42.14% were wild-type. In some cases, allele distribution depended on region. Molecular studies of more genes involved in hereditary non-syndromic SNHL are required to completely confirm the molecular basis of hearing loss in Mexican population.     

Spectrum of GJB2 (Cx26) gene mutations in Iranian Azeri patients with nonsyndromic autosomal recessive hearing loss

Objective

Hereditary hearing impairment is a genetically heterogeneous disorder. In spite of this, mutations in the GJB2 gene, encoding connexin 26 (Cx26), are a major cause of nonsyndromic recessive hearing loss in many countries and are largely dependent on ethnic groups. The purpose of our study was to characterize the type and prevalence of GJB2 mutations among Azeri population of Iran.

Methods

Fifty families presenting autosomal recessive nonsyndromic hearing loss from Ardabil province of Iran were studied for mutations in GJB2 gene. All DNA samples were screened for c.35delG mutation by ARMS PCR. Samples from patients who were normal for c.35delG were analyzed for the other variations in GJB2 by direct sequencing. In the absence of mutation detection, GJB6 was screened for the del(GJB6-D13S1830) and del(GJB6-D13S1854).

Result

Thirteen families demonstrated alteration in the Cx26 (26%). The 35delG mutation was the most common one, accounting for 69.2% (9 out of 13 families). All the detected families were homozygous for this mutation. Two families were homozygous for delE120 and 299-300delAT mutations. We also identified a novel mutation: c.463-464 delTA in 2 families resulting in a frame shift mutation.

Conclusion

Our results suggest that c.35delG mutation in the GJB2 gene is the most important cause of GJB2 related deafness in Iranian Azeri 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.     

Long term speech perception after cochlear implant in pediatric patients with GJB2 mutations

Objectives

To determine the long term effect of cochlear implant (CI) in children with GJB2-related deafness in Japan.

Methods

Genetic testing was performed on 29 children with CI. The speech perception in 9 children with GJB2 gene-related deafness fitted with CI was compared with those in matched 10 children who were diagnosed as having no genetic loci. The average follow-up period after CI was 55.9 months and 54.6 months, respectively.

Results

A definitive inherited hearing impairment could be confirmed in 12 (41.4%) of the 29 CI children, including 10 with GJB2-related hearing impairment and 2 with SLC26A4-related hearing impairment. The results of IT-MAIS, word or speech perception testing under the noise, and development of speech perception and production testing using the Enjoji scale were slightly better for the GJB2 group after CI than for the control group without statistical significant difference.

Conclusion

The long-term results of this study show that CI is also effective in the development of speech performance after CI in Japanese children with GJB2-related hearing impairments as HL due to other etiologies.     

GJB2 mutation spectrum in 209 hearing impaired individuals of predominantly Caribbean Hispanic and African descent

Objective

The purpose of the study is to determine whether Caribbean Hispanic and African admixture populations have a paucity of mutations in GJB2, encoding connexin 26.

Methods

We reported the paucity of mutations in GJB2 and deletions in GJB6 in Caribbean Hispanic and African admixture populations in the Bronx, NY, in 2007 [1]. We have now collected 102 additional probands with non-syndromic sensorineural hearing impairment (NSHI), for a total of 209. We describe here a presentation of the combined data.

Results

Of the 209 probands, 36% have affected family members with NSHI and the rest have sporadic occurrence. Of the familial cases, 43% had a first-degree relative affected, and the remainder a more distant relative. The hearing impairment ranged from unilateral mild to bilateral profound, with 76% exhibiting bilateral NSHI (BLNSHI). The single coding exon of the GJB2 gene was sequenced in 209 probands, PCR screening for del(GJB6-D13S1830) and sequencing of the non-coding exon of GJB2 to look for the known splice site mutation was performed in 32 NSHI patients with a heterozygous variation in GJB2, and multiplex ligation-dependent probe amplification (MLPA) testing of GJB2 and GJB6 exon deletions or amplifications (P163 GJB-WFS1 kit) was done in 70 probands. Eight unrelated individuals had biallelic GJB2 mutations, representing 4% of our entire cohort, or 5% of our probands with BLNSHI. Of 127 probands of Hispanic or African descent with BLNSHI, six (4.7%) had biallelic pathogenic mutations, three (2.3%) had monoallelic mutations and 118 (93%) had no disease-causing mutations in GJB2. At the same time, no major deletions were identified either by PCR screening (del(GJB6-D13S1830)) or by MLPA analysis (GJB2 or GJB6), and no subjects had the known splice site mutation in GJB2.

Conclusion

These results demonstrate that GJB2 is not the major contributor to the genetic basis of NSHI for the Bronx minority admixture populations.     

De novo dominant mutation of GJB2 in two Chinese families with nonsyndromic hearing loss

Background

Mutations in the GJB2 gene are the most common cause of nonsyndromic autosomal recessive sensorineural hearing loss. A few mutations in GJB2 have also been reported to cause dominant nonsyndromic or syndromic hearing loss. However, de novo or dominant mutation in GJB2 is not common in Chinese populations.

Methods

Two probands with hearing impairment from unrelated Chinese families are reported here. Temporal CT scan, complete physical (including skin and hair) and otoscopic examinations, and an audiological study, including tympanometry, auditory brainstem response (ABR), auditory steady-state response (ASSR), and 40 Hz-auditory event-related potential (40 Hz-AERP), were carried out. The two exons of GJB2, the coding exons of SLC26A4, and mitochondrial 12S rRNA were sequenced.

Results

Sequencing of GJB2 in the two cases showed a heterozygous c.551G>A(p.R184Q) mutation, which was not found in other family members. Additionally, no other mutation in GJB2 was identified in the two family members. Paternity was confirmed by genotype analysis of 15 informative short tandem repeats (STRs) from the chromosomes. Sequence analysis of the coding exons of SLC26A4 and mitochondrial 12S rRNA was performed but no sequence aberration or deletion was found.

Conclusions

A de novo GJB2 p.R184Q mutation can cause severe-to-profound bilateral sensorineural hearing impairment. Although not common in Chinese patients with hearing loss, it is important to identify the specific phenotype and genotype correlations of the de novo dominant mutation in GJB2.     

Frequency of GJB2 and del(GJB6-D13S1830) mutations among an Ecuadorian mestizo population

Objective

The frequency of GJB2 mutations and of the del(GJB6-D13S1830) mutation has not been established among the Ecuadorian mestizo population diagnosed with autosomal recessive non-syndromic hearing loss. A genetic analysis was therefore designed in order to do so.

Methods

The sample population included 111 subjects of which 26 were autosomal recessive non-syndromic hearing loss probands. Posterior to PCR amplification, sequencing analysis of exon 2 was used for mutational detection of the GJB2 gene; a multiplex PCR method was used for detection of the del(GJB6-D13S1830) mutation. The ratio of subjects with a certain state of the mutation (heterozygous/homozygous) is expressed as a percentage and significant differences between probands and controls were calculated using Fisher's exact test; P < 0.05 was considered significant.

Results

A total of 104 mutations belonging to 8 allelic variations were identified. The most common being the V27I (58.9%); however, as this variation is a non-pathogenic polymorphism, Q7X, with a total of 19 mutated alleles, was the most frequent mutation (18.3%). The V27I polymorphism was the only variation distributed homogenously among probands and controls (P = 0.351). Based on physical analyses of multiple patients we confirm that Q7X causes a non-syndromic form of hearing loss and propose that it is a possible predominant mutation in the Ecuadorian population.

Conclusions

This is the first study of its kind among the Ecuadorian population and a preliminary step in establishing GJB2 and del(GJB6-D13S1830) mutational frequencies in this population; it is also the first to report of such a high frequency of the Q7X mutation. The data presented here brings Ecuador a step closer to providing more efficient treatment for a broader number of patients; additionally, it contributes to a better understanding of the relationship between autosomal recessive non-syndromic hearing loss and mutations on the GJB2 gene.     

贵阳市盲聋哑学校非综合征性耳聋分子病因学分析——GJB2 235delC突变和线粒体DNA 12SrRNA A1555G突变筛查报告

目的 进行贵州省贵阳地区非综合征性耳聋分子病因学调查。方法 对贵阳市盲聋哑学校150名聋哑学生进行耳聋病因问卷调查、纯音听阈测试，对其中139名非综合征性耳聋患者进行线粒体DNA 12SrDNA A1555G点突变和GJB2基因235delC突变限制性内切酶的分析。结果 139名非综合征性耳聋患者中。6例（4132％）存在线粒体DNA 12SrDNA A1555G点突变；17例（12．23％）存在GJB2 235delC纯合突变；9例（6．47％）存在GJB2235delC杂合突变，在分子水平能够明确诊断者占23．02％。结论 贵阳地区耳聋患者存在较高的遗传性耳聋发生率，线粒体DNA A1555G突变发生率和GJB2 235delC突变发生率均高于全国平均水平。耳聋基因诊断技术可以应用在地区性耳聋病因调查中进行快速筛查、诊断，并可达到防止再出生聋儿，指导聋儿康复等积极效果。     

Identification of novel variants in the TMIE gene of patients with nonsyndromic hearing loss

Objective

To determine whether variants of the TMIE gene are causes of nonsyndromic deafness in Taiwan.

Methods

A genetic survey was made from 370 individuals, with 250 nonsyndromic hearing loss and 120 normal hearing individuals. Genomic DNA was extracted from peripheral blood leukocytes and then subjected to PCR to amplify selected exons and flanking introns of the TMIE gene; the amplified products were screened for base variants by autosequence. Data from the two groups were then compared using Fisher's two-tailed exact test and Armitage's trend test.

Results

The analysis revealed 7 novel variants in the TMIE gene. Of the 7 variants, 5 variants were found in both nonsyndromic hearing loss and normal hearing group. Both allelic and genotype frequencies of these sequence changes did not differ significantly between patients and controls (P > 0.05). However, a missense variant (c.257G > A) and one promoter variant (g.1-219A > T) were found in two patients with nonsyndromic hearing loss. Family study and microsatellite analysis found that c.257G > A variant is not inherited from his parents. The c.257G > A variant encodes a protein with glutamine at position 86 instead of arginine (p.R86Q), a residue that is conserved in mammals but different in fish, and predicted to be extracellular.

Conclusions

Despite the fact that the frequency of TMIE variants in our study subjects was low, we suggested that c.257G > A (p.R86Q) variant is a de novo and may be as a risk factor for the development of hearing loss in Taiwanese.     

Identification of a novel mutation in the SLC26A4 gene in an Italian with fluctuating sensorineural hearing loss

Pendred syndrome is an autosomal recessive disorder characterized by congenital sensorineural deafness, goitre and defective iodide organification. Congenital and profound hearing loss is the hallmark of the syndrome, while goitre and thyroid dysfunction are highly variable even within the same family. Clinical features are due to altered formation of pendrin, a chloride/iodide transporter protein expressed in the inner ear, thyroid gland and kidney. A novel substitution was found in exon 7 of the pendrin encoding gene (SLC26A4) that leads to a stop codon, S314X. The new variation was found in compound heterozygosity with L445W mutation in a hearing impaired patient with bilateral Mondini's dysplasia and goitre.     

A novel TECTA mutation confirms the recognizable phenotype among autosomal recessive hearing impairment families

Mutations in the TECTA gene result in sensorineural non-syndromic hearing impairment. TECTA-related deafness can be inherited autosomal dominantly (designated as DFNA8/12) or autosomal recessively (as DFNB21). The alpha-tectorin protein, which is encoded by the TECTA gene, is one of the major components of the tectorial membrane in the inner ear. Six mutations in the TECTA gene have already been reported in families segregating autosomal recessive non-syndromic hearing impairment. In this study, seventy-five Iranian families segregating autosomal recessive non-syndromic hearing impairment were analyzed for homozygosity at the DFNB21 locus by genotyping two short tandem repeat markers closely linked to the TECTA gene. Allelic segregation consistent with possible linkage to the DFNB21 locus was found in 1/75 families studied. By sequencing all 23 coding exons of TECTA, a 16bp deletion (c.6203-6218del16) in exon 21, leading to a frameshift, segregating with the hearing loss was found. All 3 affected individuals of this family have moderate-to-severe hearing loss across all frequencies, which is more pronounced in the mid frequencies. This new mutation, as well as the six previously reported mutations in the TECTA gene, is inactivating. All of these mutations lead to an easily recognized audiometric profile of moderate to severe hearing impairment as presented by the family in this study too. The TECTA autosomal recessive non-syndromic deafness phenotype differs from the typical profound deafness phenotype that is seen in most families segregating autosomal recessive non-syndromic deafness. On the basis of the recognizable phenotype, we recommend mutation screening of TECTA in families with this hearing phenotype.     

GJB2 mutations are rare in probands with hearing loss in Chinese assortative mating families

Objective

GJB2 mutation is recognized as the prevalent causes of non-syndromic hearing loss (NSHL) worldwide. However, the mutation profiles of GJB2 are rarely reported in deafness probands of the assortative mating family. Therefore, this study aimed to characterize the frequencies of GJB2 mutations in probands with hearing loss in the assortative mating family in Hubei province, Central China.

Methods

Genomic DNA was extracted from blood samples of 29 probands with hearing loss. The target fragments were amplified by polymerase chain reaction (PCR) and subjected to sequencing to identify sequence variations.

Results

None of 29 probands harbored homozygous mutation in GJB2, while GJB2 heterozygous mutations c.134G>A, c.139G>T, and a deletion c.235delC were identified in three probands, respectively.

Conclusion

GJB2 mutations are rare in Chinese probands of assortative mating families. Screening for responsible genes other than GJB2 is necessary for NSHL in these probands.     

A novel recessive truncating mutation in MYO15A causing prelingual sensorineural hearing loss

Hearing loss (HL) is one of the most common human defects which affects millions of people globally. The identification of deafness-related genes or loci may facilitate basic and clinical translational research on this disorder. Here, we investigated a Chinese family with autosomal recessive non-syndromic hearing impairment. Using targeted massively parallel sequencing, we identified a novel homozygous mutation, c.3525_3526insA and p.Q1175fsX1188 (NM_016239), in exon 2 of MYO15A. Sanger sequencing confirmed that affected siblings were homozygous for the mutation, whereas both normal hearing parents were heterozygous. The mutation was absent in 96 healthy controls and public databases. The insertion leads to a frameshift and a truncated form of the protein, resulting in the pathogenic effect of hearing loss for the patients. Mutations in exon 2 of MYO15A may cause a less severe phenotype, facilitating the rapid identification of mutations in exon 2 among the 66 exons when linkage of less severe hearing loss to Deafness, Autosomal Recessive 3 (DFNB3) is detected. Our data provide additional molecular information for establishing a better genotype–phenotype understanding of DFNB3.     

中国西北地区耳聋家系中GJB2基因突变频率分析

目的 分析在中国西北地区耳聋家系人群与散发人群之间GJB2基因突变频率的差异性,探讨GJB2基因突变在西北地区耳聋家系人群中的发生频率及其特点.方法 收集中国西北地区29个家系的87例耳聋患者、散发非综合征型感音神经性耳聋患者169例及听力正常人117例血样,提取外周血DNA后,进行聚合酶链反应扩增GJB2基因编码区,将扩增产物进行直接测序.运用DNAStar5.0软件进行测序结果分析,对各组CJB2基因突变频率进行统计学分析.结果 87例家系耳聋患者中存在GJB2致病突变2S例,占32.18%;169例散发耳聋患者中GJB2基因致病突变24例.占14.20%;117例正常对照人群发现GJB2基因突变携带者5例,占4.27%.结论 GJB2基因突变在中国西北地区家系耳聋患者与散发耳聋人群的发生频率存在统计学差异(X2=11.474,P<0.05),对存在CJB2基因突变的耳聋患者进一步对其家系成员重点进行该基因的突变筛查具有重要意义.