Mutations inGJB2,GJB6, and mitochondrial DNA are rare in African American and Caribbean Hispanic individuals with hearing impairment

Global prevalence of the mitochondrial MT-RNR1 A1555G variant in non-syndromic hearing loss: A systematic review and meta-analysis

Non-syndromic sensorineural hearing loss (NSHL) significantly affects quality of life and is often associated with the MT-RNR1 A1555G variant. This meta-analysis investigated the global prevalence of the A1555G variant, considering factors such as age of onset and aminoglycoside exposure. A systematic review of 97 studies published between 2000 and the present included 31,013 participants. The overall prevalence of the A1555G variant was 3.37 %, with higher rates in East Asia. Subgroup analysis revealed variant frequencies of 7.24 % in postlingual deafness cases and 1.45 % in prelingual cases. Familial cases and those with aminoglycoside exposure showed significantly higher prevalence rates (9.2 % vs. 1.9 %). These findings underscore the variant's critical role in NSHL etiology and the necessity of incorporating genetic screening into clinical practices, especially for patients with aminoglycoside exposure.

Etiologic Diagnosis of Genetic Hearing Loss in an Ethnically Diverse Deafness Cohort

INTRODUCTION

Hearing loss is a common sensory disorder that impacts patients across the lifespan. Many genetic variants have been identified that contribute to non-syndromic hearing loss. Yet, genetic testing is not routinely administered when hearing loss is diagnosed, particularly in adults. In this study, genetic testing was completed in patients with known hearing loss.

METHODS

A total of 104 patients who were evaluated for hearing loss were enrolled and received genetic testing.

RESULTS

Of those 104 patients, 39 had available genetic testing, 20 had one missing allele, and 45 yielded no genetic diagnosis. Of the 39 cases with genetic testing data, 24 were simplex cases, and 15 were multiplex cases. A majority of patients presented with an autosomal recessive inheritance pattern (n = 32), 26 of whom presented with congenital hearing loss. 38% of cases were positive for GJB2 mutation with c.35delG being the most common pathogenic variant. These findings are consistent with previous literature suggesting GJB2 mutations are the most common causes of non-syndromic hearing loss.

CONCLUSION

Given the frequency of genetic variants in patients with hearing loss, genetic testing should be considered a routine part of the hearing loss work-up, particularly as gene therapies are studied and become more widely available.

LAY SUMMARY

Many genetic variants have been identified that contribute to non-syndromic hearing loss. Given the frequency of genetic variants in patients with hearing loss, genetic testing should be considered a routine part of the hearing loss work-up.

Genetic etiology of non-syndromic hearing loss in Latin America

Latin America comprises all countries from South and Central America, in addition to Mexico. It is characterized by a complex mosaic of regions with heterogeneous genetic profiles regarding the geographical origin of the ancestors and proportions of admixture between the Native American, European and African components. In the first years following the findings of the role of the GJB2/GJB6 genes in the etiology of hearing loss, most scientific investigations about the genetics of hearing loss in Latin America focused on assessing the frequencies of pathogenic variants in these genes. More recently, modern techniques allowed researchers in Latin America to make exciting contributions to the finding of new candidate genes, novel mechanisms of inheritance in previously known genes, and characterize a wide diversity of variants, many of them unique to Latin America. This review aimed to provide a general landscape of the genetic studies about non-syndromic hearing loss in Latin America and their main scientific contributions. It allows the conclusion that, although there are similar contributions of some genes, such as GJB2/GJB6, when compared to European and North American countries, Latin American populations revealed some peculiarities that indicate the need for tailored strategies of screening and diagnosis to specific geographic regions.

First glance at the molecular etiology of hearing loss in French-Canadian families from Saguenay-Lac-Saint-Jean's founder population

The French-Canadian population of Saguenay-Lac-Saint-Jean is known for its homogenous genetic background. The hereditary causes of hearing loss were previously unexplored in this population. Individuals with hearing loss were referred from the otorhinolaryngology, pediatrics and family physicians' clinics to the medical genetics service at the Centre intégré universitaire de santé et de services sociaux du Saguenay-Lac-Saint-Jean between June 2015 and March 2021. A regional clinical evaluation strategy was developed. Samples from 63 individuals belonging to 41 families were sent independently to different molecular clinical laboratories and index cases were analyzed through comprehensive multigene panels, with a diagnostic rate of 54%. Sixteen hearing loss causal variants were identified in 12 genes, with eight of these variants not been previously reported in the literature. Recurrent variants were present in four genes, suggesting a possible founder effect, while GJB2 gene variants were scarce. A comprehensive multigene panel approach as part of the proposed clinical evaluation strategy offers a high diagnostic yield for this population.

Recent advancements in understanding the role of epigenetics in the auditory system

Sensorineural deafness in mammals is most commonly caused by damage to inner ear sensory epithelia, or hair cells, and can be attributed to genetic and environmental causes. After undergoing trauma, many non-mammalian organisms, including reptiles, birds, and zebrafish, are capable of regenerating damaged hair cells. Mammals, however, are not capable of regenerating damaged inner ear sensory epithelia, so that hair cell damage is permanent and can lead to hearing loss. The field of epigenetics, which is the study of various phenotypic changes caused by modification of genetic expression rather than alteration of DNA sequence, has seen numerous developments in uncovering biological mechanisms of gene expression and creating various medical treatments. However, there is a lack of information on the precise contribution of epigenetic modifications in the auditory system, specifically regarding their correlation with development of inner ear (cochlea) and consequent hearing impairment. Current studies have suggested that epigenetic modifications influence differentiation, development, and protection of auditory hair cells in cochlea, and can lead to hair cell degeneration. The objective of this article is to review the existing literature and discuss the advancements made in understanding epigenetic modifications of inner ear sensory epithelial cells. The analysis of the emerging epigenetic mechanisms related to inner ear sensory epithelial cells development, differentiation, protection, and regeneration will pave the way to develop novel therapeutic strategies for hearing loss.

Connexin Genes Variants Associated with Non-Syndromic Hearing Impairment: A Systematic Review of the Global Burden

Mutations in connexins are the most common causes of hearing impairment (HI) in many populations. Our aim was to review the global burden of pathogenic and likely pathogenic (PLP) variants in connexin genes associated with HI. We conducted a systematic review of the literature based on targeted inclusion/exclusion criteria of publications from 1997 to 2020. The databases used were PubMed, Scopus, Africa-Wide Information, and Web of Science. The protocol was registered on PROSPERO, the International Prospective Register of Systematic Reviews, with the registration number “CRD42020169697”. The data extracted were analyzed using Microsoft Excel and SPSS version 25 (IBM, Armonk, New York, United States). A total of 571 independent studies were retrieved and considered for data extraction with the majority of studies (47.8% (n = 289)) done in Asia. Targeted sequencing was found to be the most common technique used in investigating connexin gene mutations. We identified seven connexin genes that were associated with HI, and GJB2 (520/571 publications) was the most studied among the seven. Excluding PLP in GJB2, GJB6, and GJA1 the other connexin gene variants (thus GJB3, GJB4, GJC3, and GJC1 variants) had conflicting association with HI. Biallelic GJB2 PLP variants were the most common and widespread variants associated with non-syndromic hearing impairment (NSHI) in different global populations but absent in most African populations. The most common GJB2 alleles found to be predominant in specific populations include; p.Gly12ValfsTer2 in Europeans, North Africans, Brazilians, and Americans; p.V37I and p.L79Cfs in Asians; p.W24X in Indians; p.L56Rfs in Americans; and the founder mutation p.R143W in Africans from Ghana, or with putative Ghanaian ancestry. The present review suggests that only GJB2 and GJB3 are recognized and validated HI genes. The findings call for an extensive investigation of the other connexin genes in many populations to elucidate their contributions to HI, in order to improve gene-disease pair curations, globally.

GJB2 and GJB6 Genetic Variant Curation in an Argentinean Non-Syndromic Hearing-Impaired Cohort

Genetic variants in GJB2 and GJB6 genes are the most frequent causes of hereditary hearing loss among several deaf populations worldwide. Molecular diagnosis enables proper genetic counseling and medical prognosis to patients. In this study, we present an update of testing results in a cohort of Argentinean non-syndromic hearing-impaired individuals. A total of 48 different sequence variants were detected in genomic DNA from patients referred to our laboratory. They were manually curated and classified based on the American College of Medical Genetics and Genomics/Association for Molecular Pathology ACMG/AMP standards and hearing-loss-gene-specific criteria of the ClinGen Hearing Loss Expert Panel. More than 50% of sequence variants were reclassified from their previous categorization in ClinVar. These results provide an accurately interpreted set of variants to be taken into account by clinicians and the scientific community, and hence, aid the precise genetic counseling to patients.

Diagnostic and therapeutic applications of genomic medicine in progressive, late-onset, nonsyndromic sensorineural hearing loss

The progressive, late-onset, nonsyndromic, sensorineural hearing loss (PNSHL) is the most common cause of sensory impairment globally, with presbycusis affecting greater than a third of individuals over the age of 65. The etiology underlying PNSHL include presbycusis, noise-induced hearing loss, drug ototoxicity, and delayed-onset autosomal dominant hearing loss (AD PNSHL). The objective of this article is to discuss the potential diagnostic and therapeutic applications of genomic medicine in PNSHL. Genomic factors contribute greatly to PNSHL. The heritability of presbycusis ranges from 25 to 75%. Current therapies for PNSHL range from sound amplification to cochlear implantation (CI). PNSHL is an excellent candidate for genomic medicine approaches as it is common, has well-described pathophysiology, has a wide time window for treatment, and is amenable to local gene therapy by currently utilized procedural approaches. AD PNSHL is especially suited to genomic medicine approaches that can disrupt the expression of an aberrant protein product. Gene therapy is emerging as a potential therapeutic strategy for the treatment of PNSHL. Viral gene delivery approaches have demonstrated promising results in human clinical trials for two inherited causes of blindness and are being used for PNSHL in animal models and a human trial. Non-viral gene therapy approaches are useful in situations where a transient biologic effect is needed or for delivery of genome editing reagents (such as CRISPR/Cas9) into the inner ear. Many gene therapy modalities that have proven efficacious in animal trials have potential to delay or prevent PNSHL in humans. The development of new treatment modalities for PNSHL will lead to improved quality of life of many affected individuals and their families.

Systematic Review of Pathogenic GJB2 Variants in the Latino Population

OBJECTIVES

Define the extent to which GJB2-related hearing loss is responsible for non-syndromic hearing loss (NSHL) in the Latino population.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

GJB2 and GJB6 Mutations in Non-Syndromic Childhood Hearing Impairment in Ghana

Our study aimed to investigate GJB2 (connexin 26) and GJB6 (connexin 30) mutations associated with non-syndromic childhood hearing impairment (HI) as well as the environmental causes of HI in Ghana. Medical reports of 1,104 students attending schools for the deaf were analyzed. Families segregating HI, as well as isolated cases of HI of putative genetic origin were recruited. DNA was extracted from peripheral blood followed by Sanger sequencing of the entire coding region of GJB2. Multiplex PCR and Sanger sequencing were used to analyze the prevalence of GJB6-D3S1830 deletion. Ninety-seven families segregating HI were identified, with 235 affected individuals; and a total of 166 isolated cases of putative genetic causes, were sampled from 11 schools for the deaf in Ghana. The environmental factors, particularly meningitis, remain a major cause of HI impairment in Ghana. The male/female ratio was 1.49. Only 59.6% of the patients had their first comprehensive HI test between 6 to 11 years of age. Nearly all the participants had sensorineural HI (99.5%; n = 639). The majority had pre-lingual HI (68.3%, n = 754), of which 92.8% were congenital. Pedigree analysis suggested autosomal recessive inheritance in 96.9% of the familial cases. GJB2-R143W mutation, previously reported as founder a mutation in Ghana accounted for 25.9% (21/81) in the homozygous state in familial cases, and in 7.9% (11/140) of non-familial non-syndromic congenital HI cases, of putative genetic origin. In a control population without HI, we found a prevalent of GJB2-R143W carriers of 1.4% (2/145), in the heterozygous state. No GJB6-D3S1830 deletion was identified in any of the HI patients. GJB2-R143W mutation accounted for over a quarter of familial non-syndromic HI in Ghana and should be investigated in clinical practice. The large connexin 30 gene deletion (GJB6-D3S1830 deletion) does not account for of congenital non-syndromic HI in Ghana. There is a need to employ next generation sequencing approaches and functional genomics studies to identify the other genes involved in most families and isolated cases of HI in Ghana.

Frequency of GJB2 mutations, GJB6-D13S1830 and GJB6-D13S1854 deletions among patients with non-syndromic hearing loss from the central region of Iran

Background

In the present study, we investigate the prevalence of the GJB2 gene mutations, and deletions in the GJB6 gene, namely del (GJB6‐D13S1830) and del (GJB6‐D13S1854), in patients with autosomal recessive non‐syndromic hearing loss (ARNSHL) from the central region of Iran.

Methods

One hundred and thirty‐one unrelated ARNSHL cases from the central part of Iran were recruited. Among them, 81% (106 cases) had at least two affected relatives. Coding and noncoding regions of the GJB2 gene were sequenced. Multiplex PCR was used for analysis of del (GJB6‐D13S1830) and del (GJB6‐D13S1854) deletions in GJB6.

Results

The GJB2 variants were found in 16.79% (22/131) of the patients. The pathogenic variants were 21/131 (16.03%). The nonpathogenic variants were 1/131 (0. 07%). Allele frequency of the c.35delG as the pathogenic variant was the most common with 59.52% (25/42). The remaining pathogenic variants were c.235delC, p.T8M, p.R32H, p.R143Q, p.R143W, c‐23+1G>A. The only nonpathogenic variant was polymorphism p.V27I. Further segregation analysis showed that variant of p.R143Q might have incomplete penetrance. None of the patients had targeted deletions in the GJB6 gene.

Conclusion

In comparison with reports from other areas of Iran, c.35delG demonstrates the highest frequency within the central region (accounting for 57.14% of cases), probably resulting from the founder effect and consanguineous marriage. The pathology of ARNSHL in such patients could be attributed to defects in Connexin 26 encoded by GJB2.

Systematic Review of Hearing Loss Genes in the African American Population

OBJECTIVE

Literature review of the genetic etiology of hearing loss (HL) in the African American (AA) population.

DATA SOURCES

PubMed, EBSCO, and CINAHL were accessed from 1966 to 2018.

REVIEW METHODS

PRISMA guidelines were followed. Search terms included permutations of "hearing loss," "African American," "black," and "genetic"; "African American" was then cross-referenced against documented HL genes. AA subjects included in multiethnic cohorts of genetic HL testing were identified by searching the key terms "hearing loss" and "ethnic cohort" and "genetic." The Q-Genie tool was used in the quality assessment of included studies. An allele frequency meta-analysis of pathogenic GJB2 variants in the AA population was performed and stratified by hearing status.

RESULTS

Four hundred seventeen articles were reviewed, and 26 met our inclusion criteria. Ten studies were included in the GJB2 meta-analysis. In the general AA population, pathogenic GJB2 variants are rare, including the 35delG allele, which displayed a carrier frequency of 0.05%. Pathogenic variants were discovered in seven nonsyndromic HL genes (GJB2, MYO3A, TECTA, STRC, OTOF, MYH14, TMC1), eight syndromic HL genes, and one mitochondrial HL gene. Recent comprehensive genetic testing using custom genetic HL testing platforms has yielded only a 26% molecular diagnosis rate for HL etiologies in the AA population.

CONCLUSIONS

Investigators should be encouraged to provide an ethnic breakdown of results. Sparse literature and poor diagnosis rates indicate that genes involved in HL in the AA population have yet to be identified. Future explorative investigations using next-generation sequencing technologies, such as whole-exome sequencing, into the AA population are warranted.

The Prevalence of Ultrarapid Metabolizers of Codeine in a Diverse Urban Population

OBJECTIVE

To examine the prevalence of ultrarapid metabolizers of codeine among children in an ethnically diverse urban community.

STUDY DESIGN

Cross-sectional study.

SETTING

A tertiary care academic children's hospital in the Bronx, New York.

SUBJECTS AND METHODS

In total, 256 children with nonsyndromic congenital sensorineural hearing loss were analyzed. DNA was assessed for 63 previously described single-nucleotide polymorphisms (SNPs) and copy number variants (CNVs) known to alter the function and expression of the CYP2D6 gene primarily responsible for codeine metabolism. The rate of CYP2D6 metabolism was predicted based on participants' haplotype.

RESULTS

Ethnic distribution in the study subjects paralleled recent local census data, with the largest portion (115 children, 45.8%) identified as Hispanic or Latino. A total of 154 children (80.6%) had a haplotype that corresponds to extensive codeine metabolism, 18 children (9.42%) were identified as ultrarapid metabolizers (UMs), and 16 children (8.37%) were intermediate metabolizers. Only 3 children in our cohort (1.57%) were poor metabolizers. Patients identifying as Caucasian or Hispanic had an elevated incidence of UMs (11.3% and 11.2%, respectively) with extensive variability within subpopulations.

CONCLUSIONS

The clinically significant rate of ultrarapid metabolizers reinforces safety concerns regarding the use of codeine and related opiates. A patient-targeted approach using pharmacogenomics may mitigate adverse effects by individualizing the selection and dosing of these analgesics.

Frequency of GJB2 mutations in patients with nonsyndromic hearing loss from an ethnically characterized Brazilian population

Introduction

In different parts of the world, mutations in the GJB2 gene are associated with nonsyndromic hearing loss, and the homozygous 35delG mutation (p.Gly12Valfs*2) is a major cause of hereditary hearing loss. However, the 35delG mutation is not equally prevalent across ethnicities, making it important to study other mutations, especially in multiethnic countries such as Brazil.

Objective

This study aimed to identify different mutations in the GJB2 gene in patients with severe to profound nonsyndromic sensorineural hearing loss of putative genetic origin, and who were negative or heterozygote for the 35delG mutation.

Methods

Observational study that analyzed 100 ethnically characterized Brazilian patients with nonsyndromic severe to profound sensorineural hearing loss, who were negative or heterozygote for the 35delG mutation. GJB2 mutations were detected by DNA-based sequencing in this population. Participants’ ethnicities were identified as Latin European, Non-Latin European, Jewish, Native, Turkish, Afro-American, Asian and Others.

Results

Sixteen participants were heterozygote for the 35delG mutation; 14 participants, including three 35delG heterozygote's, had nine different alterations in the GJB2 gene. One variant, p.Ser199Glnfs*9, detected in two participants, was previously unreported. Three variants were pathogenic (p.Trp172*, p.Val167Met, and p.Arg75Trp), two were non-pathogenic (p.Val27Ile and p.Ile196Thr), and three variants were indeterminate (p.Met34Thr, p.Arg127Leu, and p.Lys168Arg). Three cases of compound heterozygosity were detected: p.[(Gly12Valfs*2)];[(Trp172*)], p.[(Gly12Valfs*2)](;)[(Met34Thr)], and p.[(Gly12Valfs*2)(;)[(Ser199Glnfs*9)]).

Conclusion

This study detected previously unclassified variants and one case of previously unreported compound heterozygosity.

Genetic basis of hearing loss in Spanish, Hispanic and Latino populations

Hearing loss (HL) is the most common neurosensory disorder affecting humans. The screening, prevention and treatment of HL require a better understanding of the underlying molecular mechanisms. Genetic predisposition is one of the most common factors that leads to HL. Most HL studies include few Spanish, Hispanic and Latino participants, leaving a critical gap in our understanding about the prevalence, impact, unmet health care needs, and genetic factors associated with hearing impairment among Spanish, Hispanic and Latino populations. The few studies which have been performed show that the gene variants commonly associated with HL in non-Spanish and non-Hispanic populations are infrequently responsible for hearing impairment in Spanish as well as Hispanic and Latino populations (hereafter referred to as Hispanic). To design effective screening tools to detect HL in Spanish and Hispanic populations, studies must be conducted to determine the gene variants that are most commonly associated with hearing impairment in this racial/ethnic group. In this review article, we summarize gene variants and loci associated with HL in Spanish and Hispanic populations. Identifying new genetic variants associated with HL in Spanish and Hispanic populations will pave the way to develop effective screening tools and therapeutic strategies for HL.

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.

The genetic basis of deafness in populations of African descent

Hearing loss is the most common sensorineural disorder worldwide and is associated with more than 1000 mutations in more than 90 genes. While mutations in genes such as GJB2 (gap-junction protein β 2) and GJB6 (gap-junction protein β 6) are highly prevalent in Caucasian, Asian, and Middle Eastern populations, they are rare in both native African populations and those of African descent. The objective of this paper is to review the current knowledge regarding the epidemiology and genetics of hearing loss in African populations with a focus on native sub-Saharan African populations. Environmental etiologies related to poor access to healthcare and perinatal care account for the majority of cases. Syndromic etiologies including Waardenburg, Pendred and Usher syndromes are uncommon causes of hearing loss in these populations. Of the non-syndromic causes, common mutations in GJB2 and GJB6 are rarely implicated in populations of African descent. Recent use of next-generation sequencing (NGS) has identified several candidate deafness genes in African populations from Nigeria and South Africa that are unique when compared to common causative mutations worldwide. Researchers also recently described a dominant mutation in MYO3a in an African American family with non-syndromic hearing loss. The use of NGS and specialized panels will aid in identifying rare and novel mutations in a more cost- and time-effective manner. The identification of common hearing loss mutations in indigenous African populations will pave the way for translation into genetic deafness research in populations of African descent worldwide.

Secondary structural analysis of the carboxyl-terminal domain from different connexin isoforms

The connexin carboxyl-terminal (CxCT) domain plays a role in the trafficking, localization, and turnover of gap junction channels, as well as the level of gap junction intercellular communication via numerous post-translational modifications and protein-protein interactions. As a key player in the regulation of gap junctions, the CT presents itself as a target for manipulation intended to modify function. Specific to intrinsically disordered proteins, identifying residues whose secondary structure can be manipulated will be critical toward unlocking the therapeutic potential of the CxCT domain. To accomplish this goal, we used biophysical methods to characterize CxCT domains attached to their fourth transmembrane domain (TM4). Circular dichroism and nuclear magnetic resonance were complementary in demonstrating the connexin isoforms that form the greatest amount of α-helical structure in their CT domain (Cx45 > Cx43 > Cx32 > Cx50 > Cx37 ≈ Cx40 ≈ Cx26). Studies compared the influence of 2,2,2-trifluoroethanol, pH, phosphorylation, and mutations (Cx32, X-linked Charcot-Marie Tooth disease; Cx26, hearing loss) on the TM4-CxCT structure. While pH modestly influences the CT structure, a major structural change was associated with phosphomimetic substitutions. Since most connexin CT domains are phosphorylated throughout their life cycle, studies of phospho-TM4-CxCT isoforms will be critical toward understanding the role that structure plays in regulating gap junction function.

A Novel C-Terminal CIB2 (Calcium and Integrin Binding Protein 2) Mutation Associated with Non-Syndromic Hearing Loss in a Hispanic Family

Hearing loss is a complex disorder caused by both genetic and environmental factors. Previously, mutations in CIB2 have been identified as a common cause of genetic hearing loss in Pakistani and Turkish populations. Here we report a novel (c.556C>T; p.(Arg186Trp)) transition mutation in the CIB2 gene identified through whole exome sequencing (WES) in a Caribbean Hispanic family with non-syndromic hearing loss. CIB2 belongs to the family of calcium-and integrin-binding (CIB) proteins. The carboxy-termini of CIB proteins are associated with calcium binding and intracellular signaling. The p.(Arg186Trp) mutation is localized within predicted type II PDZ binding ligand at the carboxy terminus. Our ex vivo studies revealed that the mutation did not alter the interactions of CIB2 with Whirlin, nor its targeting to the tips of hair cell stereocilia. However, we found that the mutation disrupts inhibition of ATP-induced Ca2+ responses by CIB2 in a heterologous expression system. Our findings support p.(Arg186Trp) mutation as a cause for hearing loss in this Hispanic family. In addition, it further highlights the necessity of the calcium binding property of CIB2 for normal hearing.

Screening of genetic alterations related to non-syndromic hearing loss using MassARRAY iPLEX® technology

BACKGROUND

Recent advances in molecular genetics have enabled to determine the genetic causes of non-syndromic hearing loss, and more than 100 genes have been related to the phenotype. Due to this extraordinary genetic heterogeneity, a large percentage of patients remain without any molecular diagnosis. This condition imply the need for new methodological strategies in order to detect a greater number of mutations in multiple genes. In this work, we optimized and tested a panel of 86 mutations in 17 different genes screened using a high-throughput genotyping technology to determine the molecular etiology of hearing loss.

METHODS

The technology used in this work was the MassARRAY iPLEX® platform. This technology uses silicon chips and DNA amplification products for accurate genotyping by mass spectrometry of previous reported mutations. The generated results were validated using conventional techniques, as direct sequencing, multiplex PCR and RFLP-PCR.

RESULTS

An initial genotyping of control subjects, showed failures in 20 % of the selected alterations. To optimize these results, the failed tests were re-designed and new primers were synthesized. Then, the specificity and sensitivity of the panel demonstrated values above 97 %. Additionally, a group of 180 individuals with NSHL without a molecular diagnosis was screened to test the diagnostic value of our panel, and mutations were identified in 30 % of the cases. In 20 % of the individuals, it was possible to explain the etiology of the HL. Mutations in GJB2 gene were the most prevalent, followed by other mutations in in SLC26A4, CDH23, MT-RNR1, MYO15A, and OTOF genes.

CONCLUSIONS

The MassARRAY technology has the potential for high-throughput identification of genetic variations. However, we demonstrated that optimization is required to increase the genotyping success and accuracy. The developed panel proved to be efficient and cost-effective, being suitable for applications involving the molecular diagnosis of hearing loss.

Massively Parallel Sequencing for Genetic Diagnosis of Hearing Loss: The New Standard of Care

OBJECTIVE

To evaluate the use of new genetic sequencing techniques for comprehensive genetic testing for hearing loss.

DATA SOURCES

Articles were identified from PubMed and Google Scholar databases using pertinent search terms.

REVIEW METHODS

Literature search identified 30 studies as candidates that met search criteria. Three studies were excluded, and 8 studies were found to be case reports. Twenty studies were included for review analysis, including 7 studies that evaluated controls and 16 studies that evaluated patients with unknown causes of hearing loss; 3 studies evaluated both controls and patients.

CONCLUSIONS

In the 20 studies included in the review analysis, 426 control samples and 603 patients with unknown causes of hearing loss underwent comprehensive genetic diagnosis for hearing loss using massively parallel sequencing. Control analysis showed a sensitivity and specificity >99%, sufficient for clinical use of these tests. The overall diagnostic rate was 41% (range, 10%-83%) and varied based on several factors, including inheritance and prescreening prior to comprehensive testing. There were significant differences in platforms available with regard to the number and type of genes included and whether copy number variations were examined. Based on these results, comprehensive genetic testing should form the cornerstone of a tiered approach to clinical evaluation of patients with hearing loss along with history, physical examination, and audiometry and can determine further testing that may be required, if any.

IMPLICATIONS FOR PRACTICE

Comprehensive genetic testing has become the new standard of care for genetic testing for patients with sensorineural hearing loss.

Genetics of hearing loss in Africans: use of next generation sequencing is the best way forward

Hearing loss is the most common communication disorder affecting about 1-7/1000 births worldwide. The most affected areas are developing countries due toextensively poor health care systems. Environmental causes contribute to 50-70% of cases, specifically meningitis in sub-Saharan Africa. The other 30-50% is attributed to genetic factors. Nonsyndromic hearing loss is the most common form of hearing loss accounting for up to 70% of cases. The most common mode of inheritance is autosomal recessive. The most prevalent mutations associated with autosomal recessive nonsyndromic hearing loss (ARNSHL) are found within connexin genes such as GJB2, mostly in people of European and Asian origin. For example, the c.35delG mutation ofGJB2 is found in 70% of ARNSHL patients of European descentand is rare in populations of otherethnicities. Other GJB2 mutations have been reported in various populations. The second most common mutations are found in theconnexin gene, GJB6, also with a high prevalencein patients of European descent. To date more than 60 genes have been associated with ARNSHL. We previously showed that mutations in GJB2, GJB6 and GJA1 are not significant causes of ARNSHL inpatients from African descents, i.e. Cameroonians and South AfricansIn order to resolve ARNSHL amongst sub-Saharan African patients, additional genes would need to be explored. Currently at least 60 genes are thought to play a role in ARNSHL thus the current approach using Sanger sequencing would not be appropriate as it would be expensive and time consuming. Next Generation sequencing (NGS) provides the best alternative approach. In this review, we reported on the success of using NGSas observed in various populations and advocate for the use of NGS to resolve cases of ARNSHL in sub-Saharan African populations.

Non-syndromic hearing loss gene identification: A brief history and glimpse into the future

From the first identified non-syndromic hearing loss gene in 1995, to those discovered in present day, the field of human genetics has witnessed an unparalleled revolution that includes the completion of the Human Genome Project in 2003 to the $1000 genome in 2014. This review highlights the classical and cutting-edge strategies for non-syndromic hearing loss gene identification that have been used throughout the twenty year history with a special emphasis on how the innovative breakthroughs in next generation sequencing technology have forever changed candidate gene approaches. The simplified approach afforded by next generation sequencing technology provides a second chance for the many linked loci in large and well characterized families that have been identified by linkage analysis but have presently failed to identify a causative gene. It also discusses some complexities that may restrict eventual candidate gene discovery and calls for novel approaches to answer some of the questions that make this simple Mendelian disorder so intriguing.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Sequencing of GJB2 in Cameroonians and Black South Africans and comparison to 1000 Genomes Project Data Support Need to Revise Strategy for Discovery of Nonsyndromic Deafness Genes in Africans

Mutations in the GJB2 gene, encoding connexin 26, could account for 50% of congenital, nonsyndromic, recessive deafness cases in some Caucasian/Asian populations. There is a scarcity of published data in sub-Saharan Africans. We Sanger sequenced the coding region of the GJB2 gene in 205 Cameroonian and Xhosa South Africans with congenital, nonsyndromic deafness; and performed bioinformatic analysis of variations in the GJB2 gene, incorporating data from the 1000 Genomes Project. Amongst Cameroonian patients, 26.1% were familial. The majority of patients (70%) suffered from sensorineural hearing loss. Ten GJB2 genetic variants were detected by sequencing. A previously reported pathogenic mutation, g.3741_3743delTTC (p.F142del), and a putative pathogenic mutation, g.3816G>A (p.V167M), were identified in single heterozygous samples. Amongst eight the remaining variants, two novel variants, g.3318-41G>A and g.3332G>A, were reported. There were no statistically significant differences in allele frequencies between cases and controls. Principal Components Analyses differentiated between Africans, Asians, and Europeans, but only explained 40% of the variation. The present study is the first to compare African GJB2 sequences with the data from the 1000 Genomes Project and have revealed the low variation between population groups. This finding has emphasized the hypothesis that the prevalence of mutations in GJB2 in nonsyndromic deafness amongst European and Asian populations is due to founder effects arising after these individuals migrated out of Africa, and not to a putative "protective" variant in the genomic structure of GJB2 in Africans. Our results confirm that mutations in GJB2 are not associated with nonsyndromic deafness in Africans.

In search of genetic markers for nonsyndromic deafness in Africa: a study in Cameroonians and Black South Africans with the GJB6 and GJA1 candidate genes

Deafness is the most common sensory disability in the world and has a variety of causes. Globally, mutations in GJB2 have been shown to play a major role in nonsyndromic deafness, but this has not been seen in Africans. Two other connexin genes, GJB6 and GJA1, have been implicated in hearing loss but have seldom been investigated in African populations. We set out to investigate the role of genetic variation in GJB6 and GJA1 in a group of Cameroonian and South African Blacks with nonsyndromic recessive hearing loss. A subset of 100 patients, affected with nonsyndromic hearing loss, from a cohort that was previously shown not to have GJB2 mutation, was analyzed by Sanger sequencing of the entire coding regions of GJB6 and GJA1. In addition, the large-scale GJB6-D3S1830 deletion was also investigated. No pathogenic mutation was detected in either GJB6 or GJA1, nor was the GJB6-D3S1830 deletion detected. There were no statistically significant differences in sequence variants between patients and controls. Mutations in GJB6 and GJA1 are not a major cause of nonsyndromic deafness in this group of Africans from Cameroon and South Africa. Currently, there is no sufficient evidence to support their testing in a clinical setting for individuals of African ancestry.

Identification of four novel connexin 26 mutations in non-syndromic deaf patients: genotype-phenotype analysis in moderate cases

This paper presents a mutation as well as a genotype-phenotype analysis of the GJB2 and GJB6 genes in 476 samples from non-syndromic unrelated Argentinean deaf patients (104 familial and 372 sporadic cases). Most of them were of prelingual onset (82 %) and 27 % were cochlear implanted. Variation of sequences was detected in 171 of the 474 patients (36 %). Overall, 43 different sequence variations were identified in GJB2 and GJB6. Four of them are reported for the first time in GJB2: c.233dupG, p.Ala78Ser, p.Val190Asp and p.Cys211Tyr. Mutations in GJB6 were detected in 3 % of patients [nine del(GJB6-D13S1830) and three del(GJB6-D13S1854)]. Of the 43 different variations identified in GJB2, 6 were polymorphisms and of the others, 10 (27 %) were truncating and 27 (73 %) were nontruncating. Patients with two truncating mutations had significantly worse hearing impairment than all other groups. Moderate phenotypes were observed in a group of patients carrying biallelic mutations (23 %). This work shows the high prevalence of GJB2 mutations in the Argentinean population and presents an analysis of moderate phenotypes in our cohort.

Mutation detection in GJB2 gene among Malays with non-syndromic hearing loss

OBJECTIVES

To identify the mutations in the GJB2 gene and to determine its association with non-syndromic hearing loss in Malays.

METHODS

A comparative cross sectional study was conducted on a group of children from the deaf schools and the normal schools. A total of 91 buccal cell samples of non-syndromic hearing loss and 91 normal hearing children were taken. Polymerase chain reaction was used to amplify the coding region of GJB2 gene. The PCR product of GJB2 coding region was preceded with screening for mutations using denaturing high performance liquid chromatography (dHPLC) and mutations detected were confirmed by DNA sequencing.

RESULTS

Twelve sequence variations including mutations and polymorphisms were found in 32 patients and 37 control subjects. The variations were G4D, V27I, E114G, T123N, V37I and R127H in both groups, W24X, R32H, 257_259 del CGC and M34L in patients only and I203T and V153I in control subjects only. There were no association between homozygous (P=0.368) or heterozygous (P=0.164) GJB2 gene and non-syndromic hearing loss.

CONCLUSIONS

The types of GJB2 gene mutation were different and vary in Malay non-syndromic hearing loss as compared to the other races. Furthermore, the mutation did not associate with hearing loss in the population. Other related genes are believed to be involved and need to be sought in this group of patients.

A systematic review and meta-analysis of 235delC mutation of GJB2 gene

Background

The 235delC mutation of GJB2 gene is considered as a risk factor for the non-syndromic hearing loss (NSHL), and a significant difference in the frequency and distribution of the 235delC mutation has been described world widely.

Methods

A systematic review was performed by means of a meta-analysis to evaluate the influence of the 235delC mutation on the risk of NSHL. A literature search in electronic databases using keywords “235delC”, “GJB2” associated with “carrier frequency” was conducted to include all papers from January 1999 to June 2011. A total of 36 papers were included and there contained 13217 cases and 6521 controls derived from Oceania, American, Europe and Asian.

Results

A remarkable heterogeneity between these studies was observed. The combined results of meta-analysis showed that the 235delC mutant increased the risk of NSHL (OR = 7.9, 95%CI 4.77 ~ 13.11, P <0.00001). Meanwhile, heterogeneity of genetic effect was also observed due to the ethnic specificity and regional disparity. Therefore, the stratified meta-analysis was subsequently conducted and the results indicated that the 235delC mutation was significantly correlated with the risk of NHSL in the East Asian and South-east Asian populations (OR = 12.05, 95%CI 8.33~17.44, P <0.00001), but not significantly in the Oceania and European populations (OR = 10.36, 95%CI: 4.68~22.96, Z = 1.68, P >0.05).

Conclusions

The 235delC mutation of GJB2 gene increased the risk of NHSL in the East Asian and South-east Asian populations, but non-significantly associated with the NSHL susceptibility in Oceania and European populations, suggesting a significant ethnic specificity of this NSHL-associated mutation.

Segregation of a new mutation in SLC26A4 and p.E47X mutation in GJB2 within a consanguineous Tunisian family affected with Pendred syndrome

OBJECTIVE

Recessive mutations of the SLC26A4 (PDS) gene on chromosome 7q31 can cause sensorineural hearing loss with goiter (Pendred syndrome) or non-syndromic autosomal recessive hearing loss (DFNB4). Furthermore, mutations in the GJB2 gene results in autosomal recessive (DFNB1) and dominant (DFNA3) non-syndromic hearing loss. The aim of the present study was to characterize a family with Pendred syndrome affected by severe to profound HL and presenting goiter.

METHODS

Affected members underwent detailed audiologic examination and characterization. DNA samples from family members were genotyped with polymorphic microsatellite markers and sequencing of the SLC26A4 and GJB2 genes was performed. A total of 25 families with non-syndromic hearing loss were screened for the common p.E47X mutation in the GJB2 gene by direct dideoxy sequencing.

RESULTS

Genetic microsatellite analysis showed linkage to the 7q22-q31 chromosomal region and mutation analysis revealed a novel frameshift mutation (c.451delG) in the SLC26A4 gene. Screening of the GJB2 gene in one patient, displayed a homozygous p.E47X mutation, together with a heterozygous c.451delG mutation. Screening of 25 families with HL showed frequent segregation of the p.E47X mutation, which was homozygous in five of these families. Haplotype analysis using microsatellite markers and single nucleotide polymorphisms (SNPs) closely flanking the GJB2 gene, revealed the presence of two disease-associated-haplotypes suggesting the presence of at least, two founder effects carrying the p.E47X non-sense mutation in the Tunisian population.

CONCLUSIONS

The segregation of both SLC26A4 and GJB2 mutations in the family illustrates once again the unexpected intra-familial genetic heterogeneity in consanguineous families and highlights the difficulty of genetic counselling in such families. In addition, our results disclose the existence of founder effects in the Tunisian population.

Common molecular etiologies are rare in nonsyndromic Tibetan Chinese patients with hearing impairment

BACKGROUND

Thirty thousand infants are born every year with congenital hearing impairment in mainland China. Racial and regional factors are important in clinical diagnosis of genetic deafness. However, molecular etiology of hearing impairment in the Tibetan Chinese population living in the Tibetan Plateau has not been investigated. To provide appropriate genetic testing and counseling to Tibetan families, we investigated molecular etiology of nonsyndromic deafness in this population.

METHODS

A total of 114 unrelated deaf Tibetan children from the Tibet Autonomous Region were enrolled. Five prominent deafness-related genes, GJB2, SLC26A4, GJB6, POU3F4, and mtDNA 12S rRNA, were analyzed. Inner ear development was evaluated by temporal CT. A total of 106 Tibetan hearing normal individuals were included as genetic controls. For radiological comparison, 120 patients, mainly of Han ethnicity, with sensorineural hearing loss were analyzed by temporal CT.

RESULTS

None of the Tibetan patients carried diallelic GJB2 or SLC26A4 mutations. Two patients with a history of aminoglycoside usage carried homogeneous mtDNA 12S rRNA A1555G mutation. Two controls were homozygous for 12S rRNA A1555G. There were no mutations in GJB6 or POU3F4. A diagnosis of inner ear malformation was made in 20.18% of the Tibetan patients and 21.67% of the Han deaf group. Enlarged vestibular aqueduct, the most common inner ear deformity, was not found in theTibetan patients, but was seen in 18.33% of the Han patients. Common molecular etiologies, GJB2 and SLC26A4 mutations, were rare in the Tibetan Chinese deaf population.

CONCLUSION

The mutation spectrum of hearing loss differs significantly between Chinese Tibetan patients and Han patients. The incidence of inner ear malformation in Tibetans is almost as high as that in Han deaf patients, but the types of malformation vary greatly. Hypoxia and special environment in plateau may be one cause of developmental inner ear deformity in this population.

Large-scale screening of mitochondrial DNA mutations among Iranian patients with prelingual nonsyndromic hearing impairment

Hereditary hearing impairment (HI) is a genetically heterogeneous disorder caused by mutations either in nuclear DNA (nDNA) or in mitochondrial DNA (mtDNA). The nDNA mutations account for the majority of prelingual nonsyndromic HI (NSHI). The present survey was conducted to screen for known pathogenic mtDNA mutations including A1555G, A3243G, C1494T, and A7445G to provide an accurate estimate of their prevalence in prelingual NSHI for the first time in the Iranian subpopulations. One thousand unrelated probands with NSHI (including both GJB2-negative and GJB2 heterozygote cases) and 1000 healthy matched controls were investigated using the PCR/RFLP method followed by DNA sequencing to confirm the observed mtDNA mutations. Two of the studied mutations, namely A3243G and A7445G, were each found in a single family (a frequency of 0.1% for each). Mutation screening for A3243G followed by DNA sequencing led to the identification of G3316A substitution, with no prior link to HI. Surprisingly, screening for A3243G in the studied population identified 6 cases (0.6%) in probands and 10 (1%) in normal subjects. A1555G, the most common mtDNA mutation associated with deafness in other populations, was not found in the studied samples. To conclude, our findings indicate G3316A as a nonpathogenic variant in the prelingual NSHI subpopulations of Iran and suggest that mtDNA mutations do not play a major role in the etiology of NSHI in Iran.

Molecular screening of patients with nonsyndromic hearing loss from Nanjing city of China

Hearing loss is the most frequent sensory disorder involving a multitude of factors, and at least 50% of cases are due to genetic etiology. To further characterize the molecular etiology of hearing loss in the Chinese population, we recruited a total of 135 unrelated patients with nonsyndromic sensorineural hearing loss (NSHL) for mutational screening of GJB2, GJB3, GJB6, SLC26A4, SLC26A5 IVS2-2A>G and mitochondrial 12SrRNA, tRNA(Ser(UCN)) by PCR amplification and direct DNA sequencing. The carrier frequencies of deafness-causing mutations in these patients were 35.55% in GJB2, 3.70% in GJB6, 15.56% in SLC26A4 and 8.14% in mitochondrial 12SrRNA, respectively. The results indicate the necessity of genetic screening for mutations of these causative genes in Chinese population with nonsyndromic hearing loss.

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.

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.

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.

Genetic evaluation of American minority pediatric cochlear implant recipients

OBJECTIVE

To review the results of genetic evaluation of American minority pediatric cochlear implant recipients over a 5-year period.

METHODS

Case series review of pediatric cochlear implant recipients of Caribbean Hispanic and African American admixture descent with severe to profound sensorineural hearing loss at a tertiary care children's hospital.

RESULTS

Out of 28 patients receiving cochlear implants, 14 were of Caribbean Hispanic or African American admixture ancestry. Six (43%) had environmental risk factors for sensorineural hearing loss. Eight (57%) patients had presumed genetic sensorineural hearing loss; two of whom were syndromic and six non-syndromic. Patients with no clear etiology for hearing loss were tested for Gap Junction Beta 2 (GJB2) mutations. Within this admixture group, we found no biallelic mutations in GJB2, while two patients, both with environmental risk factors for sensorineural hearing loss, had monoallelic GJB2 variants. One patient of mixed ethnicity (Caribbean Hispanic, Turkish, Macedonian), not included as part of the 14, had the common Caucasian founder mutation, 35delG, along with a heterozygous polymorphism in the GJB2 gene. This extends previous data showing a paucity of GJB2 mutations in these admixture populations.

CONCLUSIONS

We found no biallelic GJB2 mutations in our admixture cochlear implant population, and two sequence variants of the gene, only one of which was disease causing. This suggests that the incidence of GJB2 mutations in these admixture populations is low. Hence, there may be low cost-benefit of GJB2 mutation analysis in these admixture populations with severe to profound non-syndromic sensorineural hearing loss.

Infant hearing loss and connexin testing in a diverse population

PURPOSE

Previous studies of connexin-related hearing loss have typically reported on mixed age groups or adults. To further address epidemiology and natural history of connexin-related hearing loss, we conducted a longitudinal study in an ethnically diverse cohort of infants and toddlers under 3 years of age. Our study compares infants with and without connexin-related hearing loss to examine differences in the prevalence of connexin and non-connexin-related hearing loss by ethnic origin, detection by newborn hearing screening, phenotype, neonatal risk factors, and family history. This is the first study to differentiate infants with and without connexin-related hearing loss.

METHODS

We enrolled 95 infants with hearing loss from whom both exons of Cx26 were sequenced and the Cx30 deletion was assayed. Demographic, family history, newborn hearing screening data, perinatal, and audiologic records were analyzed.

RESULTS

Genetic testing identified biallelic Cx26/30 hearing loss-associated variants in 24.7% of infants with a significantly lower prevalence in Hispanic infants (9.1%). Eighty-two infants underwent newborn hearing screening; 12 infants passed, 3 had connexin-related hearing loss. No differences in newborn hearing screening pass rate, neonatal complications, or hearing loss severity were detected between infants with and without connexin-related hearing loss. Family history correlates with connexin-related hearing loss.

CONCLUSIONS

Connexin-related hearing loss occurs in one quarter of infants in an ethnically diverse hearing loss population but with a lower prevalence in Hispanic infants. Not all infants with connexin-related hearing loss fail newborn hearing screening. Family history correlates significantly with connexin-related hearing loss. Genetic testing should not be deferred because of newborn complications. These results will have an impact on genetic testing for infant hearing loss.

High frequency of heterozygosity in GJB2 mutations among patients with non-syndromic hearing loss

OBJECTIVE

To determine the prevalence of GJB2 mutations among subjects with congenital, non-syndromic, sensorineural hearing loss, within a north Indian population.

MATERIALS AND METHODS

This was a case-control study in which the frequencies of the three most prevalent GJB2 mutations (35delG, W24X and 167delT) were studied. Polymerase chain reaction restriction fragment length polymorphism assays were performed to detect these mutations. The entire coding region of the GJB2 gene was sequenced in all patients, and also in any of their family members who showed GJB2 mutations.

RESULTS

The 35delG mutation was found to be the most prevalent mutation (21 per cent), followed by the W24X mutation (7 per cent). This is the first report of the 35delG mutation in an Indian population. One patient was a compound heterozygote for 35delG/W24X. The 167delT mutation was not observed in any patient.

CONCLUSIONS

These findings challenge the classical view that the W24X variant of the GJB2 gene represents a single 'founder' mutation.