DFNB1-associated deafness in Portuguese cochlear implant users: prevalence and impact on oral outcome

Genetic Basis of Nonsyndromic Sensorineural Hearing Loss in the Sub-Saharan African Island Population of São Tomé and Príncipe: The Role of the DFNB1 Locus?

Hearing loss (HL) is a common condition with both genetic and environmental causes, and it greatly impacts global health. The prevalence of HL is reportedly higher in developing countries such as the Sub-Saharan African island of São Tomé and Príncipe, where the deaf community is estimated to be less than 1% of the population. We investigated the role of the DFNB1 locus (GJB2 and GJB6 genes) in the etiology of nonsyndromic sensorineural hearing loss (NSSHL) in São Tomé and Príncipe. A sample of 316 individuals, comprising 136 NSSHL patients (92 bilateral, 44 unilateral) and 180 controls, underwent a clinical and audiological examination. Sequencing of the GJB2 coding region and testing for the (GJB6-D13S1830) and del(GJB6-D13S1854) GJB6 deletions were performed. A total of 311 out of 316 individuals were successfully analyzed regarding the GJB2 and GJB6 genetic variations, respectively. The frequency of the GJB2 coding mutations in patients and controls was low. Some of those coding mutations are the most commonly found in Eurasian and Mediterranean populations and have also been identified in Portugal. None of the GJB6 deletions was present. The presence of certain coding variants in São Tomé and Príncipe suggests a non-Sub-Saharan genetic influx and supports the previously reported genetic influx from European (mainly Portuguese) ancestors. In summary, DFNB1 locus does not appear to be a major contributor to NSSHL in São Tomé and Príncipe. However, the presence of both pathogenic and likely pathogenic mutations in GJB2 suggests that GJB2-related NSSHL might still occur in this population, warranting further research on GJB2 testing in NSSHL cases.

Long Term Speech Perception Outcomes of Cochlear Implantation in Gap Junction Protein Beta 2 Related Hearing Loss

BACKGROUND AND OBJECTIVES

The mutation of the gap junction protein beta 2 (GJB2) gene is the predominant cause of autosomal recessive non-syndromic hearing loss. The purpose of this study was to evaluate the speech perception outcome after cochlear implantation according to the presence of a GJB2 mutation.

SUBJECTS AND METHODS

During the period from March 2004 to February 2005, 38 patients underwent cochlear implantation at Asan Medical Center. Genetic factors and speech perception were evaluated in all subjects, and the patients were grouped according to the presence of a GJB2 mutation. The two groups were carefully matched according to the age at cochlear implantation. We analyzed four mutations in the GJB2 gene: 35delG, 167delT, 235delC, and E114G. Speech perception outcomes were measured using the open set, 1 and 2 syllables, the comprehension test, the Meaningful Auditory Integration Scale, the categories of auditory performance, and the Speech Intelligibility Rating scores. The evaluations were performed before the operation, 6 and 12 months thereafter, and then annually up to nine years after cochlear implantation.

RESULTS

Fifteen patients had bi-allelic GJB2 mutations (11 with E114G and 4 with 235delC), whereas the remaining 23 had wild type alleles. For the age-matched analysis, 14 patients were selected and divided into two groups of 7 subjects each: GJB2 mutation and no mutation (i.e., deafness of unknown origin). Overall, all patients showed improvement of speech perception outcome after cochlear implantation. There was no difference in the improvement between patients with and without GJB2 mutations at the 5-year and 9-year follow up. The pattern of improvement throughout the duration of the follow-up also showed no difference between the two groups.

CONCLUSIONS

Similar outcomes of speech perception are expected after cochlear implantation in pediatric patients with or without GJB2 mutation.

Auditory outcome after cochlear implantation in patients with congenital nonsyndromic hearing loss: influence of the GJB2 status

OBJECTIVE

To compare the audiologic outcome after cochlear implantation between 2 groups of patients with congenital nonsyndromic sensorineural hearing loss.

STUDY DESIGN

Retrospective cohort study.

SETTING

Department of Otorhinolaryngology, University hospital (tertiary referral center).

PATIENTS

From a bigger pool of implanted patients, 2 groups, each numbering 30 were enrolled. The patients from the first group were diagnosed with a Connexin 26 mutation (GJB2), whereas all of the patients from the second cohort were with a wild type genotype. Both groups were age matched, 1 to 7 years old at the age of implantation, with diagnosed congenital nonsyndromic sensorineural hearing loss.

MAIN OUTCOME MEASURES

Both groups were evaluated with the help evaluation of auditory responses to speech/EARS/test battery - LiP test (Listening Progress Profile), MTP tests 3,6,12 (Monosyllabic-Trochee-Polysyllabic Test), GASP test (Glendonald Auditory Screening Procedure), and others. Follow-up period was at least 36 months.

RESULTS

Mean test scores were compared at the 1st, 6th, 12th, 24th, and 36th month. LiP outcome was significantly better (p < 0.05) for the GJB2-related cohort for the whole follow-up period except at the first month. MTP3, 6, and 12 tests displayed the same statistically significant outcome in favor of the first group. In the open-set test GASP, the difference was apparent: 1.22, 2.40, 5.59, and 7.40 mean scores at the 6th, 12th, 24, and 36th months for the first cohort versus 0.00, 0.07, 0.81, and 1.74 for the GJB2-unrelated patients.

CONCLUSION

The results from our study suggest that children with GJB2-related deafness show better auditory performance after cochlear implantation than age-matched children with GJB2-nonrelated sensorineural hearing loss.

Exploration of molecular genetic etiology for Korean cochlear implantees with severe to profound hearing loss and its implication

Background

Severe to profound sensorineural hearing loss (SNHL) requires cochlear implantation (CI) for auditory rehabilitation. Etiologic diagnoses can contribute to candidacy selection and decision-making regarding the timing of successful CI. However, few studies have been performed to address the etiologic spectrum of severe SNHL in the population where there is no consanguineous marriage and the majority of SNHL cases are sporadic in small sized families. The authors sought to comprehensively understand the etiologies of Korean cochlear implantees by incorporating the targeted resequencing of 204 candidate deafness genes (TRS-204) and a phenotype-driven candidate gene approach.

Methods

Ninety-three that consented to molecular genetic testing and underwent at least one molecular genetic test were included. Patients with a characteristic Phenotypic marker were subject to Sanger sequencing to detect variants in corresponding candidate genes. The rest of patients without any prominent phenotype were tested on GJB2. Next, TRS-204 was applied in GJB2-negative cases without any phenotypic marker. In addition, the sibling recurrence-risk of SNHL among families with non-diagnostic genotypes after TRS-204 was performed to gain insight of etiologies in non-diagnostic cases.

Results

Overall, we could find causative variants in 51 (54.8%) of the 93 cochlear implantees. Thirty (32.3%) probands could be diagnosed by direct Sanger sequencing of candidate genes selected by their phenotypes. GJB2 sequencing added 10 subjects to the group with a diagnostic genotype. TRS-204 could detect a causative variant from additional 11 cases (11.8%). We could not detect any pathogenic deletion or duplication on 204 target genes. The sibling recurrence-risk of SNHL among 42 genetically undiagnosed families with 0.03 (1/38) was significantly lower than among genetically diagnosed recessive families with 0.19 (7/37).

Conclusion

Despite that the majority of severe or more degree of SNHL occurs sporadically in Koreans, at least 54.8% of such cases that were willing to join the genetic study in the Korean population are monogenic Mendelian disorders with convincing causative variants. This study also indicates that a substantial portion of unsolved cases after applying our current protocol are predicted to have non-genetic or complex etiology rather than a Mendelian genetic disorder involving new genes beyond the 204 target genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-014-0167-8) contains supplementary material, which is available to authorized users.

Is deafness etiology important for prediction of functional outcomes in pediatric cochlear implantation?

CONCLUSIONS

Implanted children with GJB2 mutations tended to achieve better functional outcomes than the two control groups, although clear-cut significance was not always achieved. Hearing loss etiology may be considered as one of the important predictors, but complex influence of other factors on postoperative performance should be included in cautious individual counseling.

OBJECTIVE

This study aimed to detect possible associations between hearing loss etiology and postoperative rehabilitation outcomes in prelingually deaf children, with a particular focus on hereditary deafness caused by connexin mutations.

METHODS

Eighty-one of 92 prelingually deaf implanted children, tested for DFNB1 mutations, were divided into 3 etiology groups and underwent audiological evaluation in tone audiometry, speech audiometry, monosyllabic words, and categories of auditory performance (CAP), conducted 1, 3, and 5 years after implantation.

RESULTS

Statistically significant differences (p < 0.05) for tone audiometry were obtained, particularly after the first and third year post implantation, between 'connexin' and 'known' etiology groups. In speech audiometry, the monosyllabic word test, and CAP, the connexin group of children scored significantly better than the two control groups only after 3 and 5 years. Although the rate of excellent performers was higher in the connexin group, poor results were achieved in all groups in similar proportion.

Distribution and phenotype of GJB2 mutations in 102 Sicilian patients with congenital non syndromic sensorineural hearing loss

OBJECTIVE

To evaluate the frequency of GJB2 mutations and their correlation with phenotype in Sicilian non-syndromic sensorineural hearing loss (NSHL) 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 102 Sicilian NSHL patients.

RESULTS

Fifteen different mutations in GJB2 and seventeen different genotypes were detected. No GJB6 mutations were found. The hearing impairment was profound in the 64.72% of probands (mean PTA0.25-4 kHz of 88.82 ± 26.52 dB HL). A total of 81.37% of patients harboured at least one c.35delG allele; c.167delT and c.-23 + 1G> A were identified in 10.78% and the 9.8% of patients respectively; c.35delG homozygotes presented more severe hearing impairment (75.59% of profound hearing loss) and a higher mean PTA0.25-4 kHz (96.79 ± 21.11 dB HL) with respect to c.35delG/non-c.35delG and c.35delG/Wt patients (P < 0.05).

CONCLUSIONS

This work underlines the role of c.35delG, c.167delT and c.-23 + 1G> A as the most frequent causes of NSHL in Sicily. The c.35delG frequency found is similar to those reported in other populations of the Mediterranean area. The analysis of genetic and audiologic data confirmed a variability in the phenotype associated to a single genotype.

Speech Perception Outcomes after Cochlear Implantation in Children with GJB2/DFNB1 associated Deafness

BACKGROUND

Cochlear implants (CI) for the rehabilitation of patients with profound or total bilateral sensorineural hypoacusis represent the initial use of electrical fields to provide audibility in cases where the use of sound amplifiers does not provide satisfactory results.

AIMS

To compare speech perception performance after cochlear implantation in children with connexin 26-associated deafness with that of a control group of children with deafness of unknown etiology.

STUDY DESIGN

Retrospective comparative study.

METHODS

During the period from 2006 to, cochlear implantation was performed on 26 children. Eighteen of these children had undergone genetic tests for mutation of the Gap Junction Protein Beta 2 (GJB2) gene. Bi-allelic GJB2 mutations were confirmed in 7 out of 18 examined children. In order to confirm whether genetic factors have influence on speech perception after cochlear implantation, we compared the post-implantation speech performance of seven children with mutations of the GBJ2 (connexin 26) gene with seven other children who had the wild type version of this particular gene. The latter were carefully matched according to the age at cochlear implantation. Speech perception performance was measured before cochlear implantation, and one and two years after implantation. All the patients were arranged in line with the appropriate speech perception category (SPC). Non-parametric tests, Friedman ANOVA and Mann-Whitney's U test were used for statistical analysis.

RESULTS

Both groups showed similar improvements in speech perception scores after cochlear implantation. Statistical analysis did not confirm significant differences between the groups 12 and 24 months after cochlear implantation.

CONCLUSION

The results obtained in this study showed an absence of apparent distinctions in the scores of speech perception between the two examined groups and therefore might have significant implications in selecting prognostic indicators of speech perception following cochlear implantation.

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.

Prevalence of DFNB1 mutations among cochlear implant users in Slovakia and its clinical implications

Hereditary etiology plays an important role in bilateral profound deafness as a main indication for cochlear implantation. Mutations in DFNB1 locus account for most of the inherited deafness cases in Caucasians. To provide actual data on mutation prevalence among implanted deaf subpopulation, we performed DNA analysis of GJB2 and GJB6 genes in 131 unrelated Slovak cochlear implant users. Eight previously described causal mutations and one probably pathogenic missense variant (c.127G>A) were detected in the GJB2 gene in 58 (44.28%) subjects. The most common mutation found was c.35delG with frequency 83.02% of all disease alleles, followed by c.71G>A, c.1-3201G>A, c.313_326del14, c.109G>A, 167delT, c.269T>C, and c.333_334delAA. GJB6 deletion delD13S1830 was identified in only one subject, in double heterozygosity with a GJB6 mutation. Thus, the deafness cause could be clearly attributable to DFNB1 mutations in 36.64% of the patients examined. In summary, the mutation profile found in our cohort was similar to the mutation spectrum reported for Central European deaf populations. The mutation prevalence in cochlear implant users was, however, almost by 25% higher than previously established for non-implanted hearing-impaired population in Slovakia. Finally, we also demonstrate a certain variability in deafness onset in patients with causal genotype and coincidence with other risk factors for deafness. Our results underline the importance of genetic tests in all cochlear implant candidates.

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

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.

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.

Defining and evaluating success in paediatric cochlear implantation--an exploratory study

OBJECTIVES

This work is a preliminary study that sought to investigate and develop a method for defining and evaluating "success" in paediatric cochlear implantation (PCI) and to apply a process by which a clinical team could optimally achieve this aim.

METHODS

A pilot group of 25 profoundly deaf children who received a unilateral cochlear implant from 1995 to 2008 was used to develop the process. The cases displayed features that are commonly encountered in PCI. Individual case records were examined retrospectively for adverse factors that might impact on the implantation outcome with particular reference to the probability and severity of impact of each factor. Case prognosis was then rated on a 1-4 basis (1: excellent, 2: good, 3: fair, 4: poor). The subsequent outcomes were assessed using standardised speech (GFW, DEAP), language (PLS-4; CELF) and vocabulary (PPVT; EVT) assessments. Auditory performance outcomes were assessed using a new Categories of Auditory Performance Index (CAPI) that incorporated criteria, testing and scoring aspects. Family issues were also evaluated. Case outcomes were rated 1-4 as above and the prognoses and outcomes were then compared.

RESULTS

Accurate prognostication was seen in 14 cases, 5 had better outcomes than expected and 6 obtained poorer results. "Success", where the outcome equalled or exceeded the prognosis, occurred in 19 (76%) of cases. The successful group contained some "limited gains" cases where the results were nonetheless in line with expectations and parental satisfaction. The detrimental effect of delayed implantation was evident; Connexin 26 (GJB2) mutation had little influence. Poor general medical condition and adverse family situations commonly produced poorer outcomes.

CONCLUSIONS

Success in PCI is achieved when the outcome matches or exceeds the pre-operative expectations of the well-counselled family, without adverse side effects. The assessments achieved a good success rate, but further research is required to clearly identify potential problems and a skilled team is needed to evaluate their risk to the PCI outcome. Unforseen events may also intervene. Currently, differing outcome evaluation techniques impede comparison of studies, particularly in the speech and hearing domains. Rationalisation of these is recommended to facilitate future research.

Prediction of cochlear implant performance by genetic mutation: the spiral ganglion hypothesis

BACKGROUND

Up to 7% of patients with severe-to-profound deafness do not benefit from cochlear implantation. Given the high surgical implantation and clinical management cost of cochlear implantation (>$1 million lifetime cost), prospective identification of the worst performers would reduce unnecessary procedures and healthcare costs. Because cochlear implants bypass the membranous labyrinth but rely on the spiral ganglion for functionality, we hypothesize that cochlear implant (CI) performance is dictated in part by the anatomic location of the cochlear pathology that underlies the hearing loss. As a corollary, we hypothesize that because genetic testing can identify sites of cochlear pathology, it may be useful in predicting CI performance.

METHODS

29 adult CI recipients with idiopathic adult-onset severe-to-profound hearing loss were studied. DNA samples were subjected to solution-based sequence capture and massively parallel sequencing using the OtoSCOPE(®) platform. The cohort was divided into three CI performance groups (good, intermediate, poor) and genetic causes of deafness were correlated with audiometric data to determine whether there was a gene-specific impact on CI performance.

RESULTS

The genetic cause of deafness was determined in 3/29 (10%) individuals. The two poor performers segregated mutations in TMPRSS3, a gene expressed in the spiral ganglion, while the good performer segregated mutations in LOXHD1, a gene expressed in the membranous labyrinth. Comprehensive literature review identified other good performers with mutations in membranous labyrinth-expressed genes; poor performance was associated with spiral ganglion-expressed genes.

CONCLUSIONS

Our data support the underlying hypothesis that mutations in genes preferentially expressed in the spiral ganglion portend poor CI performance while mutations in genes expressed in the membranous labyrinth portend good CI performance. Although the low mutation rate in known deafness genes in this cohort likely relates to the ascertainment characteristics (postlingual hearing loss in adult CI recipients), these data suggest that genetic testing should be implemented as part of the CI evaluation to test this association prospectively.

Two portuguese cochlear implanted dizygotic twins: a case report

Individual's hearing performance after cochlear implant (CI) is variable and depends on different factors such as etiology of deafness, age at implantation, and social/family hearing environment. Here we report the case of dizygotic twins, boy and girl, presenting with neurosensorial profound deafness prior CI (age of implantation = 3.5 years old). Both parents have severe/profound deafness, since childhood, and use sign language as primary mode of communication. Clinical and genetic characterization was performed, as well as the assessment of the auditory and oral (re)habilitation after CI, applying a battery of audiological, speech, and language tests. The twin girl and the father were homozygous for the c.35delG mutation in the GJB2 gene, while the twin boy and the mother were compound heterozygotes, both monoallelic for c.35delG and for the deletion del(GJB6-D13S1830) in the GJB6 gene. The remaining hearing impaired relatives were c.35delG homozygotes. The genetic cause of deafness was thus identified in this family. Some noteworthy differences were observed regarding twins' auditory and oral performance after CI. Subsequent follow-up of these children allowed us to conclude that those differences were most likely due to the different environment in which the twins have been living than to their different GJB2/GJB6 genotypes.

Prevalence of DFNB1 mutations in Slovak patients with non-syndromic hearing loss

OBJECTIVES

Non-syndromic hearing loss is one of the most common genetically determined diseases in human. The incidence is approximately 1:700 and most of the cases are caused by mutations in specific locus - DFNB1, which contains two genes -GJB2 and GJB6. For the GJB2 gene following mutations are most prevalent in specific populations - 35delG, 235delC, W24X and 167delT for Caucasians, Asians, Indians and Ashkenazi Jews, respectively. Large deletions are common in GJB6 gene. Many other mutations and polymorphisms were found in DFNB1 focused non-syndromic hearing loss studies thus the establishment of optimal screening protocol should be based on population specific mutation screening studies and is an objective in our study.

PATIENTS AND METHODS

In our study samples from 273 non-syndromic hearing loss patients were screened for mutations in coding and non-coding part of GJB2 gene and large deletion in GJB6 gene - del(GJB6-D13S1830).

RESULTS

Causal mutation on both chromosomes was detected in 24.57% of patients, another 9.9% carried causal mutation on one chromosome. Totally 7 polymorphisms: V27I, M34T, F83L, 354 C→T, R127H, V153I, 684 C→A and 11 causal mutations: IVS1+1 G→A, 35delG, W24X, V37I, E47X, 167delT, V84M, L90P, 310del14, 333-334delAA, R184Q were detected. No patient carried the GJB6 deletion mutation (del(GJB6-D13S1830)).

CONCLUSION

According to our results sequencing of GJB2 coding regions and IVS1+1G→A specific detection should explain approximately 25% of sporadic NSHL cases and these two tests are relevant for use as routine screening protocol for NSHL in Slovakia. The GJB6 del(GJB6-D13S1830) mutation was not detected in any of NSHL samples therefore it is not necessary to implement it in our routine screening protocol.