GJB2-related Hearing Loss Research Articles

Novel GJB2 mutation c.188delT compound with c.235delC causing non-syndromic hearing loss in a Chinese family: A case report.

Congenital sensorineural hearing loss is a significant global health issue, primarily driven by genetic factors, such as mutations in the GJB2 gene. This report presents a Chinese girl with congenital deafness and a novel mutation of the GJB2 gene. A newborn Chinese girl exhibited signs of congenital deafness. Congenital deafness was confirmed through comprehensive newborn hearing screenings that included otologic, audiologic, and physical examinations. Genetic analysis revealed a compound heterozygous mutation involving c.188delT and c.235delC in the GJB2 gene, indicating a genetic basis for her hearing loss. The patient underwent cochlear implantation, which resulted in stable auditory outcomes. Despite follow-up difficulties, stable auditory outcomes were achieved post-cochlear implantation, highlighting the potential efficacy of this intervention in GJB2-related hearing loss. This case study enriches our understanding of GJB2 mutations and underscores the critical role of genetic testing in diagnosing congenital sensorineural hearing loss. It emphasizes the necessity for early intervention and sustained interdisciplinary care to enhance the quality of life for patients with genetic hearing impairment.

Research progress in delineating the pathological mechanisms of GJB2-related hearing loss.

Hearing loss is the most common congenital sensory impairment. Mutations or deficiencies of the GJB2 gene are the most common genetic cause of congenital non-syndromic deafness. Pathological changes such as decreased potential in the cochlea, active cochlear amplification disorders, cochlear developmental disorders and macrophage activation have been observed in various GJB2 transgenic mouse models. In the past, researchers generally believed that the pathological mechanisms underlying GJB2-related hearing loss comprised a K+ circulation defect and abnormal ATP-Ca2+ signals. However, recent studies have shown that K+ circulation is rarely associated with the pathological process of GJB2-related hearing loss, while cochlear developmental disorders and oxidative stress play an important, even critical, role in the occurrence of GJB2-related hearing loss. Nevertheless, these research has not been systematically summarized. In this review, we summarize the pathological mechanisms of GJB2-related hearing loss, including aspects of K+ circulation, developmental disorders of the organ of Corti, nutrition delivery, oxidative stress and ATP-Ca2+ signals. Clarifying the pathological mechanism of GJB2-related hearing loss can help develop new prevention and treatment strategies.

Comprehensive interpretation of single-nucleotide substitutions in GJB2 reveals the genetic and phenotypic landscape of GJB2-related hearing loss.

Genetic variants in GJB2 are the most frequent cause of congenital and childhood hearing loss worldwide. The purpose of this study was to delineate the genetic and phenotypic landscape of GJB2 SNV variants. All possible single-nucleotide substitution variants of the coding region of GJB2 (N = 2043) were manually curated following the ACMG/AMP hearing loss guidelines. As a result, 60 (2.9%), 177 (8.7%), 1499 (73.4%), 301 (14.7%) and 6 (0.3%) of the variants were classified as pathogenic, likely pathogenic, variant of uncertain significance, likely benign, and benign, respectively. 53% (84/158) of the pathogenic/likely pathogenic missense variants were not present in ClinVar. The second transmembrane domain and the 310 helix were highly enriched for pathogenic missense variants, while the intracellular loops were tolerant to variation. The N-terminal tail and the extracellular loop showed high clustering of variants that are associated with syndromic or dominant non-syndromic hearing loss. In conclusion, our study interpreted all possible single-nucleotide substitution coding variants, characterized novel clinically significant variants in GJB2, and revealed significant genotype-phenotype correlations at this common hearing loss locus. Our work provides a prototype for other genes with similarly high genetic and phenotypic heterogeneity.

Disease-associated variants of Gap Junction Beta 2 protein (GJB2) in the deaf population of Southern Punjab of Pakistan.

Hearing impairment (HI) is a highly heterogeneous genetic disorder and is classified into nonsyndromic (without any other clinical manifestations) and syndromic (if combined with other clinical presentations) forms. Variations in GJB2 gene are the leading cause of autosomal recessive nonsyndromic hearing loss (ARNSHL) in several populations worldwide. This study was carried out to investigate the prevalence of GJB2 variations in severe-to-profound hearing impaired families of Southern Punjab of Pakistan. Ten families segregating ARNSHL were recruited from different areas of the region. Sanger sequencing of GJB2 coding region was carried out. In two out of ten families, NM_004004:c.*71G>A (p.(Trp24*)) and NM_004004:c.358_360del (p.(Glu120del)) homozygous variants were identified as the cause of hearing loss. Our study showed that GJB2-related hearing loss accounts for at least 20% of all cases with severe-to-profound hearing loss in the Southern Punjab population of Pakistan.

Impact of Pan-Ethnic Expanded Carrier Screening in Improving Population Health Outcomes: Proceedings from a Multi-Stakeholder Virtual Roundtable Summit, June 25, 2020.

Impact of Pan-Ethnic Expanded Carrier Screening in Improving Population Health Outcomes: Proceedings from a Multi-Stakeholder Virtual Roundtable Summit, June 25, 2020.

Systematic Review of Pathogenic GJB2 Variants in the Latino Population.

Define the extent to which GJB2-related hearing loss is responsible for non-syndromic hearing loss (NSHL) in the Latino population. Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines were followed. PubMed and MEDLINE were accessed from 1966 to 2019 using permutations of the MeSH terms: "Hearing Loss," "Hearing Impairment," "Deafness," "Latin American," "Latino," "GJB2," and "Genetic." Additionally, countries designated as Latino by the US Office of Management and Bureau were cross-referenced as key terms against the aforementioned search criteria. Exclusion criteria included non-English publications, a non-Latino study population, and literature not investigating GJB2. An allele frequency analysis of pathogenic GJB2 variants in the Latino population was performed and stratified by country of origin and reported ethnicity. One hundred twenty two unique studies were identified of which 64 met our inclusion criteria. Forty three studies were included in the GJB2 systematic review. A total of 38 pathogenic GJB2 variants were identified across 20 countries in the Latino population. The prevalence of pathogenic GJB2 variants varied by country; however, were generally uncommon with the exception of c.35delG (p.Gly12Valfs*) which displayed an allele frequency of 3.1% in the combined Latino population; ranging from 21% in Colombia to 0% in Guatemala. Variation in the prevalence of pathogenic GJB2 variants by country likely reflect the heterogeneous nature of ethnic ancestral contributions to the Latino population. Additional research utilizing next generation sequencing might aid in the development of assays for high throughput diagnosis of inherited hearing loss in the multitude of ethnic sub-groups that comprise this and other traditionally marginalized populations.

Degradation and modification of cochlear gap junction proteins in the early development of age-related hearing loss

Age-related hearing loss (ARHL) is the progressive, bilateral loss of high-frequency hearing in elderly people. Mutations in GJB2, encoding the cochlear gap junction protein connexin26 (Cx26), are the most frequent cause of hereditary deafness; however, a common molecular pathology between ARHL and GJB2-related hearing loss has not been reported. Here, we investigated the quantitative change in expression and molecular pathology of Cx26 in ARHL. We used C57BL/6J mice as a model of ARHL. Hearing levels that were evaluated by auditory brainstem response thresholds increased gradually between 4 and 32 weeks of age and increased sharply at 36 weeks. Gap junctions in the cochleae of 4-week-old mice had linear plaques along cell–cell junction sites. In contrast, the cochleae from 32-week-old mice had significantly shorter gap junctions. Severe hair cell loss was not observed during this period. Based on western blotting, Cx26 and connexin30 (Cx30) levels were significantly decreased at 32 weeks compared with 4 weeks.Moreover, Cx26 was more significantly enriched in the hydrophilic fraction at 4 weeks but was more significantly enriched in the hydrophobic fraction at 32 weeks, indicating an age-related conversion of this biochemical property. Thus, the hydrophobic conversion of Cx26 and disruption of gap junction proteins and plaques may be involved in the pathogenesis of ARHL and may occur before severe hair cell degeneration.

OTOF-related auditory neuropathy spectrum disorder

Of this study was to estimate the prevalence of OTOF mutations in Russian children with ANSD and evaluate audiological and clinical features of OTOF-related ANSD. 28 children with bilateral ANSDwere enrolled in the investigation. Two step genetic testing was performed: first step - GJB2 gene testing to exclude GJB2-related hearing loss; second step - NGS-based sequencing to explore another 35 hearing loss genes (including OTOF). OTOF mutations, including 6 new variants, were found in 5 children with ANSD (18%). All 5 children had no risk factors for hearing loss and passed hearing screening. OAE and cochlear microphonics were present till the last testing at the age of 4-5 years. ABR were not detectable. The ASSR were measurable bilaterally at all frequencies in all cases, but they did not correlate with behavioral thresholds that revealed severe hearing loss. Hearing thresholds were stable during follow up period. 3 children underwent cochlear implantation. After cochlear implantation auditory nerve action potentials to electric stimulation were detected within normal range. Genetic testing of children with ANSD and first of all OTOF testing enables to reveal hearing loss etiology and provide the optimal rehabilitation approach, including cochlear implantation, as early as possible.

Generation of Functional CX26-Gap-Junction-Plaque-Forming Cells with Spontaneous Ca2+ Transients via a Gap Junction Characteristic of Developing Cochlea.

Mutation of the gene GJB2, encoding connexin 26 (CX26; also known as gap junction beta 2), is the most frequent cause of hereditary deafness worldwide. CX26 is expressed in cochlear nonsensory cells, such as cochlear supporting cells, and forms gap junction plaques (GJPs) at cell-cell borders. Cochlear CX26-GJP-forming cells (Cx26GJCs) are thought to be an important therapeutic target for treatment of hereditary deafness. Nevertheless, the generation of Cx26GJCs-such as cochlear supporting cells-from embryonic stem/induced pluripotent stem (ES/iPS) cells has not been reported to date. Here, we detail a novel strategy for differentiating iPS cells into functional Cx26GJCs such as are found in cochlea. Several assays to characterize the phenotype of iPS-derived Cx26GJCs are described, including qRT-PCR, immunohistological analysis, morphological analysis, a scrape-loading and dye transfer assay, and calcium imaging. This in vitro model has applications in the establishment of inner-ear cell therapies and in drug screening to target GJB2-related hearing loss. © 2019 by John Wiley & Sons, Inc. Basic Protocol: Induction of mouse stem cells to create CX26-GJP-forming cells Support Protocol 1: Maintenance and passage of mouse induced pluripotent stem cells Support Protocol 2: Screening for high GJB2 and GJB6 expression in SFEBq culture using quantitative real-time PCR Support Protocol 3: Characterization of cells at different stages of differentiation by immunostaining Support Protocol 4: Ultrastructural analyses of cells at different stages of CX26-GJP-forming cell induction Support Protocol 5: Functional analyses of stem cell-derived CX26-GJP-forming cells.

Reduced postnatal expression of cochlear Connexin26 induces hearing loss and affects the developmental status of pillar cells in a dose-dependent manner

Mutations in the GJB2 gene (which encodes Connexin26 (Cx26)) are the most common cause of non-syndromic deafness. Previous studies showed that an extensive knockout of the Gjb2 gene in cochlear epithelium can cause severe deafness, significant hair cell (HC) loss and failure of pillar cells (a type of supporting cell, PCs) to differentiate in mice. This study aimed to establish different mouse models with gradient reductions of cochlear Cx26 expression and to investigate the effect of different reduced levels of cochlear Cx26 expression on hearing and development of PCs. According to the reduction in the levels of cochlear Cx26, these models were named high knockdown (KD), middle KD and low KD group. In the low KD group, the mice showed normal hearing and well-developed PCs. In the high KD group, up to 90 percent of supporting cells (SCs) lost Cx26 expression. These mice exhibited severe deafness, rapid hair cell degeneration and juvenile PCs. In the middle KD group, nearly half of SCs lost Cx26 expression. However, these mice showed a moderate deafness and a late-onset hair cell loss. Moreover, nearly all the PCs in mice of this group were in a partially differentiated state. These results indicated that reduction of postnatal expression of cochlear Cx26 induces hearing loss in a dose-dependent manner. Null Cx26 in a few SCs affects the developmental status of PCs and the hair cell degeneration pattern. The abnormal developmental status of PCs may be a potential cause of Gjb2-related hearing loss.

Developmental abnormalities in supporting cell phalangeal processes and cytoskeleton in the Gjb2 knockdown mouse model

ABSTRACTMutations in the GJB2 gene [which encodes connexin 26 (Cx26)] are the most common causes of hereditary hearing loss in humans, and previous studies showed postnatal development arrest of the organ of Corti in different Cx26-null mouse models. To explore the pathological changes and the mechanism behind the cochlear abnormalities in these mice further, we established transgenic mouse models by conditional knockdown of cochlear Cx26 at postnatal day (P) 0 and P8. Auditory brainstem responses were recorded and the morphological features in the organ of Corti were analyzed 18 days after Cx26 knockdown. Mice in the P0 knockdown group displayed severe hearing loss at all frequencies, whereas mice in the P8 knockdown group showed nearly normal hearing. In the P8 knockdown group, the organ of Corti displayed normal architecture, and no ultrastructural changes were observed. In the P0 knockdown group, the phalangeal processes of Deiter's cells did not develop into finger-like structures, and the formation of microtubules in the pillar cells was significantly reduced; moreover, the amount of acetylated α-tubulin was reduced in pillar cells. Our results indicate that Gjb2 participates in postnatal development of the cytoskeleton in pillar cells during structural maturation of the organ of Corti. In P0 knockdown mice, the reduction in microtubules in pillar cells might be responsible for the failure of the tunnel of Corti to open, and the malformed phalangeal processes might negatively affect the supporting framework of the organ of Corti, which would be a new mechanism of Gjb2-related hearing loss.

Twenty years of clinical studies of GJB2-linked hearing loss in Russia

The most common cause of congenital hereditary hearing loss was discovered 20 years ago in 1997 when GJB2 gene was revealed in the first locus of recessive hearing loss DFNB1. It encodes protein connexin 26, a structural component of the intercellular channels. Recessive mutations in this gene cause the congenital bilateral sensorineural hearing loss. For many years the aim of our work was to study the prevalence and clinical manifestations of hereditary hearing loss. Our research can be divided into three stages. In the beginning, we investigated the prevalence of GJB2 mutations in a healthy population and in the people suffering from hearing impairment. Further research was conducted in the field of clinical manifestations and evidence of the congenital character of GJB2-related hearing loss. Currently, we are working on the prevalence of mild and moderate hereditary hearing loss and the probability of its progression. Achievements in molecular genetics make it possible to establish the hereditary character of congenital hearing loss and to avoid repeated family cases. Primary prevention of hereditary hearing loss becomes real by raising the awareness of GJB2 mutations carriers.

InVitro Models of GJB2-Related Hearing Loss Recapitulate Ca2+ Transients via a Gap Junction Characteristic of Developing Cochlea.

SummaryMutation of the Gap Junction Beta 2 gene (GJB2) encoding connexin 26 (CX26) is the most frequent cause of hereditary deafness worldwide and accounts for up to 50% of non-syndromic sensorineural hearing loss cases in some populations. Therefore, cochlear CX26-gap junction plaque (GJP)-forming cells such as cochlear supporting cells are thought to be the most important therapeutic target for the treatment of hereditary deafness. The differentiation of pluripotent stem cells into cochlear CX26-GJP-forming cells has not been reported. Here, we detail the development of a novel strategy to differentiate induced pluripotent stem cells into functional CX26-GJP-forming cells that exhibit spontaneous ATP- and hemichannel-mediated Ca2+ transients typical of the developing cochlea. Furthermore, these cells from CX26-deficient mice recapitulated the drastic disruption of GJPs, the primary pathology of GJB2-related hearing loss. These in vitro models should be useful for establishing inner-ear cell therapies and drug screening that target GJB2-related hearing loss.

The high frequency of GJB2 gene mutation c.313_326del14 suggests its possible origin in ancestors of Lithuanian population.

BackgroundCongenital hearing loss (CHL) is diagnosed in 1 – 2 newborns in 1000, genetic factors contribute to two thirds of CHL cases in industrialised countries. Mutations of the GJB2 gene located in the DFNB1 locus (13q11-12) are a major cause of CHL worldwide.The aim of this cross-sectional study was to assess the contribution of the DFNB1 locus containing the GJB2 and GJB6 genes in the development of early onset hearing loss in the affected group of participants, to determine the population-specific mutational profile and DFNB1-related HL burden in Lithuanian population.MethodsClinical data were obtained from a collection of 158 affected participants (146 unrelated probands) with early onset non-syndromic HL. GJB2 and GJB6 gene sequencing and GJB6 gene deletion testing were performed. The data of GJB2 and GJB6 gene sequencing in 98 participants in group of self-reported healthy Lithuanian inhabitants were analysed.Statistic summary, homogeneity tests, and logistic regression analysis were used for the assessment of genotype-phenotype correlation.ResultsOur findings show 57.5 % of affected participants with two pathogenic GJB2 gene mutations identified. The most prevalent GJB2 mutations were c.35delG, p. (Gly12Valfs*2) (rs80338939) and c.313_326del14, p. (Lys105Glyfs*5) (rs111033253) with allele frequencies 64.7 % and 28.3 % respectively. GJB6 gene mutations were not identified in the affected group of participants. The statistical analysis revealed significant differences between GJB2(−) and GJB2(+) groups in disease severity (p = 0.001), and family history (p = 0.01). The probability of identification of GJB2 mutations in patients with various HL characteristics was estimated. The carrier rate of GJB2 gene mutations – 7.1 % (~1 in 14) was identified in the group of healthy participants and a high frequency of GJB2-related hearing loss was estimated in our population.DiscussionThe results show a very high proportion of GJB2-positive individuals in the research group affected with sensorineural HL. The allele frequency of c.35delG mutation (64.7 %) is consistent with many previously published studies in groups of affected individuals of Caucasian populations. The high frequency of the c.313_326del14 (28.3 % of pathogenic alleles) mutation in affected group of participants was an unexpected finding in our study suggesting not only a high frequency of carriers of this mutation in our population but also its possible origin in Lithuanian ancestors. The high frequency of carriers of the c.313_326del14 mutation in the entire Lithuanian population is supported by it being identified twice in the ethnic Lithuanian group of healthy participants (a frequency 2.0 % of carriers in the study group).ConclusionAnalysis of the allele frequency of GJB2 gene mutations revealed a high proportion of c. 313_326del14 (rs111033253) mutations in the GJB2-positive group suggesting its possible origin in Lithuanian forebears. The high frequency of carriers of GJB2 gene mutations in the group of healthy participants corresponds to the substantial frequency of GJB2-associated HL in Lithuania. The observations of the study indicate the significant contribution of GJB2 gene mutations to the pathogenesis of the disorder in the Lithuanian population and will contribute to introducing principles to predict the characteristics of the disease in patients.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0354-9) contains supplementary material, which is available to authorized users.

Going beyond the guidelines: a call for expanded carrier screen based on an analysis of 3,208 clinical samples

range from ancient-and-common polymorphisms with minimal effects to recent-and-rare mutations predicted to have larger effects on the phenotype. Applying NGS and IBD analysis using nuclear families, we were able to identify 5 candidate endometriosis regions that show excess genetic burden. A more complete picture of the genetics of endometriosis is likely to emerge as additional WGS data are analyzed. Supported by: Juneau Biosciences.

Evaluation of newborn screening bloodspot-based genetic testing as second tier screen for bedside newborn hearing screening

PurposeBedside newborn hearing screening is highly successful in identifying deaf or hard-of-hearing infants. However, newborn hearing screening protocols have high loss to follow-up rates. We propose that bloodspot-based genetic testing for GJB2 alleles can provide a means for rapid confirmation in a subset of infants who fail bedside newborn hearing screening. MethodsWe performed a case-control study comparing the prevalence of common GJB2 mutations from deidentified bloodspots designated as “refer” by newborn hearing screening and contemporaneously selected randomly chosen controls designated as “pass.” Between March 2006 and December 2007, 2354 spots were analyzed for common alleles, c.35delG, c.167delT, c.235delC, and p.V37I in GJB2 with a subset reanalyzed by conventional Sanger sequencing to search for additional alleles. ResultsThe prevalence of biallelic GJB2 mutations in bloodspots from infants who referred by newborn hearing screening is approximately 1 in 50 (23/1177). In contrast, one bloodspot from an infant who passed newborn hearing screening was identified to harbor biallelic GJB2 mutations. ConclusionsThese findings show that when a newborn refers by newborn hearing screening, there is a significant chance that GJB2-related hearing loss is present. Bloodspot-based genetic testing for common GJB2 alleles should be considered as second tier testing for bedside newborn hearing screening.

Impact of Consanguineous Marriages in GJB2-Related Hearing Loss in the Iranian Population: A Report of a Novel Variant

Mutations in GJB2 and GJB6 genes are the main causes of autosomal recessive nonsyndromic hearing loss (ARNSHL) in many populations. Here, we investigated GJB2 and GJB6 mutations in 114 patients from 77 affected ARNSHL families including 54 consanguineous marriages and 23 nonrelative marriages in the Iranian population. Clinical studies and genetic counseling were performed for all families. GJB2 and GJB6 genes were directly sequenced. Three known GJB6 large deletions [del(GJB6-D13S1830), del(GJB6-D13S1854), and a 920 kb deletion] were also checked by quantification of a common deleted region within the GJB6 gene. The frequency of consanguinity was 70.13% among the studied families. Biallelic GJB2 mutations were 16.67% in consanguineous marriages and 4.35% in nonrelative marriages. Mutations found were 35delG, delE120, R127H, M163V, W24X, V37I, G12D, V84A, 313-326del14, and E110K. The latter was a novel variant. Neither point mutation nor a large deletion in the GJB6 gene was found in the population. Mean frequency of GJB2 mutations was 17.92%. GJB2 mutations (and not GJB6 mutations) are the major causes of hearing loss in Iran. The role of consanguineous marriages is also highlighted in occurrence of GJB2-related hearing loss. We suggest that other genes may be involved in the population.

Frequence and the mutation spectrum of GJB2-related hearing loss in children of Dagestan as compared with the central European part of Russia

The sequencing of the entire coding region and the donor site of the splicing of the GJB2 gene has shown that prelingual neurosensory nonsyndromic autosomal recessive deafness/poor hearing in Dagestan Republic is genetically more heterogeneous than in the central European part of Russia. Thus, the number of the revealed mutations in the GJB2 gene in Dagestan was only 28% of the total number of alleles in patients tested. The main mutations in the GJB2 gene in Dagestan were represented by three forms typical for West Asia: 35delG mutation (22% of all mutant alleles), ΔE120 mutation (22%), both in the coding region, and IVS 1+1 G>A (44%) in the donor site of splicing. In addition, a novel mutation, ΔE187, was revealed in the coding region. All mutations were found in a compound heterozygous or a heterozygous state. This result allows one to explain the deafness/poor hearing by pathogenic mutations in the GJB2 gene only in 19% of Dagestan families with neurosensory nonsyndromic autosomal recessive disorders of hearing. We suggest that the origin and maintenance of the allele diversity of inherited deafness/poor hearing in Dagestan can be explained by the national and cultural peculiarities of small populations of nations of North Caucasus.

High homogeneity in auditory outcome of pediatric CI-patients with mutations in Gap-Junction-Protein Beta2

Objectives A controversy exists in the literature regarding better auditory performance of cochlear implanted children with mutations in the Gap-Junction-Protein Beta2 (GJB2) gene. This is partially due to insufficient numbers, lack of proper statistics, etc. As this represents a very important issue for the counselling clinician, the aim of the study was to analyze auditive outcome in GJB2-related hearing loss in relation to other causes and review the literature. Methods Retrospective study. 44 children with unilateral cochlea implants were assigned into 3 groups according to their cause of deafness: group A contained 13 patients with GJB2-related deafness, group B 15 with hereditary hearing loss and negative GJB2-screening, and group C 16 with a nonhereditary cause. The auditory outcome performance was evaluated by pure-tone audiograms (PTA), the Monosyllabic-Trochee-Polysyllabic-Word Test (MTP) and the Listening Progress Profile (LiP) according to the EARS-protocol (Evaluation of Auditory Response to Speech) pre- and postoperatively up to 6.5 years. Additionally the educational setting was considered. Statistical analysis included direct comparison by using mixed models and computing the variance to test for homogeneity. Results A trend towards better performance for the GJB2 group (vs. the other groups combined) was observed regarding PTA, even more pronounced for LiP/MTP. However, a significant p-value was not reached. A high homogeneity, expressed by a significant difference in the variance of MTP and LiP was observed in the GJB2 group. Differences in educational setting were not significant. Conclusions The results of the study seem to support a better auditory performance of GJB2-patients with cochlea implants due to a cochlear origin of the defect. The significant homogeneity for this group is of paramount issue for the counselling clinician and a very important observation.

DNA Sequence Analysis of SLC26A5, Encoding Prestin, in a Patient-Control Cohort: Identification of Fourteen Novel DNA Sequence Variations

BackgroundPrestin, encoded by the gene SLC26A5, is a transmembrane protein of the cochlear outer hair cell (OHC). Prestin is required for the somatic electromotile activity of OHCs, which is absent in OHCs and causes severe hearing impairment in mice lacking prestin. In humans, the role of sequence variations in SLC26A5 in hearing loss is less clear. Although prestin is expected to be required for functional human OHCs, the clinical significance of reported putative mutant alleles in humans is uncertain.Methodology/Principal FindingsTo explore the hypothesis that SLC26A5 may act as a modifier gene, affecting the severity of hearing loss caused by an independent etiology, a patient-control cohort was screened for DNA sequence variations in SLC26A5 using sequencing and allele specific methods. Patients in this study carried known pathogenic or controversial sequence variations in GJB2, encoding Connexin 26, or confirmed or suspected sequence variations in SLC26A5; controls included four ethnic populations. Twenty-three different DNA sequence variations in SLC26A5, 14 of which are novel, were observed: 4 novel sequence variations were found exclusively among patients; 7 novel sequence variations were found exclusively among controls; and, 12 sequence variations, 3 of which are novel, were found in both patients and controls. Twenty-one of the 23 DNA sequence variations were located in non-coding regions of SLC26A5. Two coding sequence variations, both novel, were observed only in patients and predict a silent change, p.S434S, and an amino acid substitution, p.I663V. In silico analysis of the p.I663V amino acid variation suggested this variant might be benign. Using Fisher's exact test, no statistically significant difference was observed between patients and controls in the frequency of the identified DNA sequence variations. Haplotype analysis using HaploView 4.0 software revealed the same predominant haplotype in patients and controls and derived haplotype blocks in the patient-control cohort similar to those generated from the International HapMap Project.Conclusions/SignificanceAlthough these data fail to support a hypothesis that SLC26A5 acts as a modifier gene of GJB2-related hearing loss, the sample size is small and investigation of a larger population might be more informative. The 14 novel DNA sequence variations in SLC26A5 reported here will serve as useful research tools for future studies of prestin.