Newborn hearing concurrent gene screening can improve care for hearing loss: a study on 14,913 Chinese newborns

Objective

Newborn hearing screening has been widely adopted and made an achievement to some degree. Current screening protocols rely solely on detecting existing auditory disorders at the time of screening and are unable to identify individuals susceptible to auditory disorders in later life. Even if the hearing loss newborn is referred, most cases could not be diagnosed until 6-12 months old with no etiology being elucidated. This study reports the first effort to combine traditional hearing screening with genetic screening to improve the efficacy of newborn hearing screening.

Methods

This study was undertaken in 12 regional hospitals located in 11 provinces of China. 14,913 newborn babies received hearing concurrent genetic screening. The hearing screening was performed with OAE or AABR. Blood sample was collected with a universal newborn genetic screening card. And three common gene, mtDNA 12S rRNA, GJB2 and SLC26A4 were screened with standard protocol.

Results

Among all the 14,913 newborns, 86.1% (12,837/14,913) individuals passed the first-step hearing screening, 7.8% (1168/14,913) babies passed only one side, and the other 6.1% (908/14,913) were bilaterally referred. Gene screening found 306 individuals had one or two mutant alleles, the carrier rate is 2.05% (306/14,913) among the entire newborn population. The risk for hearing loss was 100% (7/7) for those newborns carrying causative GJB2 or SLC26A4 mutations (homozygotes or compound heterozygotes), 14.4% (23/160) for GJB2 heterozygote carriers, 12.3% (15/122) for SLC26A2 heterozygous carriers, and the total prevalence of referral hearing screening was approximately 14.7% (45/306). However, 85.3% (261/306) newborns passed hearing screening among these carriers including 18 newborns with 12S rRNA mt.1555A>G pathogenic mutation, who would suffer from sudden hearing loss once applying aminoglycoside drugs.

Conclusion

The cohort studies provided the essential population parameters for developing effective programs for hearing care of newborns in China. Hearing concurrent gene screening in newborns may confirm the abnormal results from hearing screening tests, help to find the etiologic of the hearing loss, and better recognize infants at risk for late-onset hearing loss occurring prior to speech and language development. In conclusion, a survey on 14,913 Chinese newborns proved that concurrent genetic screening could improve newborn hearing screening for hearing defects.     

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.     

Prevalence of mutations located at the dfnb1 locus in a population of cochlear implanted children in eastern Romania

Objective

Hearing loss is one of the major public health problems, with a genetic etiology in more than 60% of cases. Connexin 26 and connexin 30 mutations are the most prevalent causes of deafness. The aim of this study is to characterize and to establish the prevalence of the GJB2 and GJB6 gene mutations in a population of cochlear implanted recipients from Eastern Romania, this being the first report of this type in our country.

Methods

We present a retrospective study that enrolled 45 Caucasian cochlear implanted patients with non-syndromic sensorineural severe to profound, congenital or progressive with early-onset idiopathic hearing loss. We performed sequential analysis of exon 1 and the coding exon 2 of the GJB2 gene including also the splice sites and analysis of the deletions del(GJB6-D13S1830), del(GJB6-D13S1854) and del(chr13:19,837,343-19,968,698).

Results

The genetic analysis of the GJB2 gene identified connexin 26 mutations in 22 patients out of 45 (12 homozygous for c.35delG, 6 compound heterozygous and 4 with mutations only on one allele). We found 6 different mutations, the most prevalent being c.35delG - found on 32 alleles, followed by p.W24* - found on 2 alleles. We did not identify the deletions del(GJB6-D13S1830), del(GJB6-D13S1854) and del(chr13:19,837,343-19,968,698).

Conclusions

Although the most prevalent mutation was c.35delG (80% from all types of mutations), unexpectedly we identified 5 more different mutations. The presence of 6 different mutations on the GJB2 gene has implications in hearing screening programs development in our region and in genetic counseling.     

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.     

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.     

Newborn genetic screening for high risk deafness-associated mutations with a new Tetra-primer ARMS PCR kit

Objective

Previous epidemiological studies indicate that GJB2, SLC26A4 or mtDNA 12S rRNA mutations were chiefly responsible for the hearing loss in children. A cost-effective method for screening deafness-associated mutations at early age is needed. This study aimed to develop a simple kit for screening of high risk deafness-associated mutations in newborns using tetra-primer amplification refractory mutation system PCR.

Methods

The screening kit was designed to detect high risk deafness-associated mutations (GJB2 c.235delC, SLC26A4 c.919-2A>G, mtDNA 12S rRNA mt.1555A>G and mt.1494C>T). The kit was able to amplify both wild-type and mutant alleles with a control fragment. The proposed method was conducted to genotype the above four deafness gene mutations in four PCR reactions. Each mutation was genotyped by a set of four primers, two allele-specific inner primers, and two common outer primers. A mismatch at the penultimate or antepenult nucleotide of the 3′ terminus was introduced in order to maximize specificity. The 16 primers were used for the amplification of genomic DNA as a template. Amplified fragments were separated by electrophoresis. We designed and validated the kit with wild and mutant type DNA samples that had been previously been confirmed by Sanger sequencing. Then 1181 newborns were enrolled, and those samples with mutations were further validated with sequencing too.

Results

Among 1181 newborns, 29 individuals had one or two mutant alleles, with the carrier rate being 2.46% (29/1181). For GJB2 c.235delC mutation, one case was homozygote and 12 cases were heterozygote carriers. For SLC26A4 c.919-2A>G mutation, 12 cases were heterozygotes carriers, and no homozygotes were found; for mtDNA 12S rRNA mt.1555A>G mutation, one case was identified; three cases of mtDNA 12S rRNA mt.1494C>T mutation were detected. All mutations were detected with high specificity. Mutation samples were confirmed via Sanger sequencing. No false positive was found.

Conclusion

A user-friendly screening kit for deafness-associated mutations was successfully developed. It provided rapid, reproducible, and cost-effective detection of deafness gene mutation without special equipment. The kit allowed the detection of the four high risk deafness-associated mutations with only 4 single tube PCR reactions. In the future, the kit could be applied to large population-based epidemiological studies for newborn hearing defects screening.     

Mutation analysis of seven consanguineous Uyghur families with non-syndromic deafness

Objective

To investigate the genetic causes of consanguineous Uyghur families with nonsyndromic deafness.

Method

Seven consanguineous Uyghur families with nonsyndromic deafness were recruited in this study and characterized for their audiometric phenotype. Mutation analysis of common deafness genes GJB2, SLC26A4 and MT-RNR1 was performed in all families by direct sequencing.

Result

Bi-allelic mutations in SLC26A4, including p.N392Y/p.N392Y, p.S57X/p.S57X and p.Q413R/p.L676Q, were detected in three families as the pathogenic causes for the deafness. No mutations were identified in GJB2 and MT-RNR1.

Conclusion

Mutations in SLC26A4 was the most common causes of the Uyghur consanguineous deaf families.     

Screening of SLC26A4, FOXI1 and KCNJ10 genes in unilateral hearing impairment with ipsilateral enlarged vestibular aqueduct

Objective

To investigate the implication of SLC26A4, FOXI and KCNJ10 genes in unilateral hearing impairment associated with ipsilateral inner ear malformation (Enlargement of the vestibular aqueduct and/or Mondini dysplasia).

Methods

We have gathered 25 patients presenting unilateral hearing impairment and ipsilateral enlarged vestibular aqueduct. For each of the patients, we have analyzed SLC26A4, FOXI1 and KCNJ10 genes sequences.

Results

The analysis of SLC26A4 revealed only eight heterozygous SLC26A4 sequence variants, three of them being novel (p.Met147Ile, p.Asn538Asn and p.Leu627Arg). None of the patients carried a second mutation on the other allele. Moreover, the SLC26A4 locus was excluded by segregation analysis in two families. No mutations were present in FOXI1 and KCNJ10 genes.

Conclusions

Together, these data suggest that SLC26A4, FOXI1 and KCNJ10 are not major determinants in unilateral deafness and enlarged vestibular aqueduct compared with their implication in Pendred syndrome and non-syndromic bilateral enlarged vestibular aqueduct.     

Identification of novel variants in the Myosin VIIA gene of patients with nonsyndromic hearing loss from Taiwan

Objective

To determine whether variants of exons 7, 11, 22 and 28 of the MYO7A gene are causes of nonsyndromic deafness in Taiwanese.

Methods

We screened a total of 331 unrelated Taiwanese individuals (age range, 4-22 years), including 231 patients with severe to profound nonsyndromic hearing loss and 100 individuals with normal hearing. Genomic DNA was extracted from peripheral blood leukocytes and then subjected to PCR to amplify selected exons and flanking introns of the MYO7A gene; the amplified products were screened for base mutations by autosequence. Data from the two groups were then compared using the chi-square (χ²) test.

Results

The analysis revealed six variants in 3 out of 4 screened exons and flanking intronic sequences of the MYO7A gene (exons 7, 11, and 22). Three missense variants were found only in patients with hearing loss and were heterozygous, including Arg206Cys, Arg206His and Thr381Met. A variant, c.IVS22+58G>A, was found in intron 22 of the MYO7A gene from both patients and control group. Allele frequencies of c.IVS22+58G>A were shown to be significant between the two groups using χ² test (P < 0.05).

Conclusion

Our results indicate that Arg206 and Thr381 residues in the motor head region of MYO7A protein are critical sites and the mutations of these residues may lead to the development of nonsyndromic deafness.     

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.     

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.     

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.     

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.     

Prevalence of GJB2 causing recessive profound non-syndromic deafness in Japanese children

Objective

GJB2 (gap junction protein, beta 2, 26 kDa: connexin 26) is a gap junction protein gene that has been implicated in many cases of autosomal recessive non-syndromic deafness. Point and deletion mutations in GJB2 are the most frequent cause of non-syndromic deafness across racial groups. To clarify the relation between profound non-syndromic deafness and GJB2 mutation in Japanese children, we performed genetic testing for GJB2.

Methods

We conducted mutation screening employing PCR and direct sequencing for GJB2 in 126 children who had undergone cochlear implantation with congenital deafness.

Results

We detected 10 mutations, including two unreported mutations (p.R32S and p.P225L) in GJB2. We identified the highest-frequency mutation (c.235delC: 44.8%) and other nonsense or truncating mutations, as in previous studies. However, in our research, p.R143W, which is one of the missense mutations, may also show an important correlation with severe deafness.

Conclusion

Our results suggest that the frequencies of mutations in GJB2 and GJB6 deletions differ among cohorts. Thus, our report is an important study of GJB2 in Japanese children with profound non-syndromic deafness.     

Absence of GJB6 mutations in Indian patients with non-syndromic hearing loss

Objective

Hearing loss is the most frequent sensory defect in human being. Genetic factors account for at least half of all cases of profound congenital deafness. The 13q11-q12 region contains the GJB2 and GJB6 genes, which code connexin 26 (CX26) and connexin 30 (CX30) proteins, respectively. Mutations in the gene GJB2, encoding the gap junction protein connexin 26, are considered to be responsible for up to 50% of familial cases of autosomal recessive non-syndromic hearing loss and for up to 15-30% of the sporadic cases. It has also been reported that mutations in the GJB6 gene contribute to autosomal recessive and autosomal dominant hearing defects in many populations. The 342-kb deletion [del(GJB6-D13S1830)] of the Cx30 gene is the second most common connexin mutation after the CX26 mutations in some NSHL populations. The aim of this study was to screen GJB6 gene mutations in Asian Indian patients with autosomal non-syndromic hearing loss.

Methods

We screened 203 non-syndromic hearing loss patients, who were negative for homozygous mutations in GJB2 gene, for GJB6-D13S1830 deletion and mutations in coding regions of GJB6 using polymerase chain reaction, denaturing high performance liquid chromatography and direct sequencing.

Results

No deleterious mutation in GJB6 gene was detected in our study cohort.

Conclusion

The present data demonstrated that mutations in the GJB6 gene are unlikely to be a major cause of non-syndromic deafness in Asian Indians.     

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.     

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.     

Prevalence of DFNB1 mutations in Argentinean children with non-syndromic deafness. Report of a novel mutation in GJB2

Objective

Mutations in DFNB1 locus, containing GJB2 (connexin 26) and GJB6 (connexin 30) genes, are the most common cause of autosomal recessive non-syndromic hearing loss. More than 100 mutations in GJB2 have been reported worldwide. Two deletions in GJB6, del(GJB6-D13S1830) and del(GJB6-D13S1854), have been found to be frequent in the Spanish population. The aim of this study was to determine the prevalence of GJB2 mutations and both GJB6 deletions in Argentinean children with non-syndromic deafness.

Methods

This study included 94 unrelated children with moderate to profound non-syndromic sensorineural hearing impairment. Molecular analysis was performed using a tiered approach. All DNA samples were screened for c.35delG mutation by PCR/RFLP. Samples from patients who were not homozygous for c.35delG were analysed for the presence of GJB6 deletions by PCR multiplex. The samples that remained unresolved after screening were further analysed by direct sequencing of GJB2 coding region. Finally, the splice site mutation IVS1 + 1G → A was analysed by PCR/RFLP.

Results

Sequence variations in the GJB2 and GJB6 genes were found in 49 of the 94 unrelated patients. The most prevalent GJB2 mutation, c.35delG, was found in 40 of the 68 pathogenic alleles with the second most common allele being p.R143W (4/68). Fourteen sequence variations other than c.35delG were identified. Seven already described mutations were present in more than one allele; among them, IVS1 + 1G → A, the rare splice site mutation flanking exon 1. In addition to known disease-related alterations, a novel GJB2 mutation, c.262G > C (p.A88P), was also identified. Six alleles were identified carrying GJB6 deletions; the most prevalent was del(GJB6-D13S1830). The frequency of the latter was found to be as high as that found in Spain from where Argentina has received one of its major immigration waves.

Conclusions

The overall frequency of GJB2/GJB6 mutations in the present sample is in agreement with other Caucasian populations. As expected, c.35delG was the most prevalent mutation. The deletion del(GJB6-D13S1830) was the second most common mutation. These findings reinforce the importance of the study of GJB2/GJB6 genes in diagnosis to provide early treatment and genetic counselling.     

A novel frameshift mutation (c.405delC) in the GJB2 gene associated with autosomal recessive hearing loss in two Tunisian families

Objectives

Mutations in GJB2 are found to be responsible for 50% of congenital autosomal recessive non-syndromic hearing loss, one of the most important mutations in this gene is the c.35delG, which is responsible for the majority of GJB2 related deafness in the Tunisian population. The aim of this study was to determine the molecular etiology of hearing loss in two Tunisian individuals.

Methods

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

Results

We identified a novel frameshift mutation in the GJB2 gene, the c.405delC resulting in a truncated protein (p.Tyr136Thrfs*32). It was found in compound heterozygosity with the c.35delG in two non-consanguineous unrelated families from Tunisia. One patient underwent a cochlear implant at 4 years. Initial evaluations post-implantation indicate a successful cochlear implant outcome since the patient began to acquire language abilities and auditory sensation.

Conclusions

With this novel GJB2 mutation, the mutational spectrum of this gene continues to broaden in our population. The occurrence of biallelic GJB2 mutations for the other deaf girl, despite the neonatal pain and hypotension due to complicated delivery, led us to confirm the importance of GJB2 screening for cochlear implant candidates regardless of the etiology of deafness in populations with a relatively high frequency of GJB2 mutation carriers.     

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.