The effect of GJB2 and SLC26A4 gene mutations on rehabilitative outcomes in pediatric cochlear implant patients

The role of SLC26A4 in bony labyrinth development and otoconial mineralization in mouse models

Inner ear malformations are predominantly attributed to developmental arrest during the embryonic stage of membranous labyrinth development. Due to the inherent difficulty in clinically assessing the status of the membranous labyrinth, these malformations are diagnosed with radiographic imaging, based on the morphological characteristics of the bony labyrinth. While extensive research has elucidated the intricacies of membranous labyrinth development in mouse models, comprehensive investigations into the developmental trajectory of the bony labyrinth, especially about its calcification process, have been notably lacking. One of the most prominent types of inner ear malformations is known as incomplete partition (IP), characterized by nearly normal external cochlear appearance but pronounced irregularities in the morphology of the modiolus and inter-scalar septa. IP type II (IP-II), also known as Mondini dysplasia, is generally accompanied by an enlargement of the vestibular aqueduct and is primarily attributed to mutations in the SLC26A4 gene. In the case of IP-II, the modiolus and inter-scalar septa of the cochlear apex are underdeveloped or missing, resulting in the manifestation of a cystic structure on radiographic imaging. In this overview, we not only explore the normal development of the bony labyrinth in mice but also present our observations on otolith mineralization. Furthermore, we investigated the specifics of bony labyrinth and otolith mineralization in Slc26a4-deficient mice, which served as an animal model for IP-II. We ensured that these findings promise to provide valuable insights for the establishment of therapeutic interventions, optimal timing, targeted sites, and preventive measures when considering the management of this condition.

Spectrum of genetic variants in bilateral sensorineural hearing loss

Background: Hearing loss (HL) is an impairment of auditory function with identified genetic forms that can be syndromic (30%) or non-syndromic (70%). HL is genetically heterogeneous, with more than 1,000 variants across 150 causative genes identified to date. The genetic diagnostic rate varies significantly depending on the population being tested. Countries with a considerably high rate of consanguinity provide a unique resource for studying rare forms of recessive HL. In this study, we identified genetic variants associated with bilateral sensorineural HL (SNHL) using whole-exome sequencing (WES) in 11 families residing in the United Arab Emirates (UAE). Results: We established the molecular diagnosis in six probands, with six different pathogenic or likely pathogenic variants in the genes MYO15A, SLC26A4, and GJB2. One novel nonsense variant, MYO15A:p.Tyr1962Ter*, was identified in a homozygous state in one family, which has not been reported in any public database. SLC26A4 and GJB2 were found to be the most frequently associated genes in this study. In addition, six variants of uncertain significance (VUS) were detected in five probands in the genes CDH23, COL11A1, ADGRV1, NLRP3, and GDF6. In total, 12 variants were observed in eight genes. Among these variants, eight missense variants (66.7%), three nonsense variants (25.0%), and one frameshift (8.3%) were identified. The overall diagnostic rate of this study was 54.5%. Approximately 45.5% of the patients in this study came from consanguineous families. Conclusion: Understanding the genetic basis of HL provides insight for the clinical diagnosis of hearing impairment cases through the utilization of next-generation sequencing (NGS). Our findings contribute to the knowledge of the heterogeneous genetic profile of HL, especially in a population with a high rate of consanguineous marriage in the Arab population.

Genetic screening of 15 hearing loss variants in 77,647 neonates with clinical follow-up

BACKGROUND

To analyze the genotype distribution and frequency of hearing loss genes in newborn population and evaluate the clinical value of genetic screening policy in China.

METHODS

Genetic screening for hearing loss was offered to 84,029 neonates between March 2019 and December 2021, of whom 77,647 newborns accepted the screening program with one-year follow-up. The genotyping of 15 hot spot variants in GJB2, GJB3, SLC26A4, and MT-RNR1 was performed on microarray platform.

RESULTS

A total of 3.05% (2369/77,647) newborns carried at least one genetic hearing loss-associated variant, indicated for early preventive management. The carrier frequency of GJB2 gene was the highest, at 1.48% (1147/77,647), followed by SLC26A4 gene at 1.07% (831/77,647), and GJB3 gene at 0.23% (181/77,647). GJB2 c.235delC variant and SLC26A4 IVS7-2A>G variant were the most common allelic variants with allele frequency of 0.6304% (979/155,294) and 0.3992% (620/155,294), respectively. 10 children are identified as homozygous or compound heterozygous for pathogenic variants (4 in GJB2, 6 in SLC26A4), and 7 of these infants had passed the hearing screening. Following up of the genetically screened newborns revealed that genetic screening detected more hearing-impaired infants than hearing screening alone. Genetic screening helped identify the infants who had passed the initial hearing screening, and reduced time for diagnosis and intervention of hearing aid. In addition, we identified 234 newborns (0.30%, 234/77,647) susceptible to preventable aminoglycoside antibiotic ototoxicity undetectable by hearing screening.

CONCLUSION

We performed the largest-scale neonatal carrier screening for hearing loss genes in Southeast China. Our results indicated that genetic screening is an important complementation to conventional hearing screening. Our practice and experience may facilitate the application and development of neonatal genetic screening policy in mainland China.

Characteristics of hearing loss-associated gene mutations: A multi-center study of 119,606 neonates in Gannan

BACKGROUND

HL is the second most common congenital disability in China, and its high incidence brings a serious burden of medical and educational sequelae. HL genetic screening enables the identification of individuals with inherited HL and carriers in a large scale.

OBJECTIVE

This study aimed to measure the detection rates of hearing loss (HL)-associated gene mutations in the Gannan population. The molecular etiology and risk factors of hereditary HL were also analyzed.

METHODS

In total, 119,606 newborns from 18 districts of Gannan were enrolled in this multi-center study conducted between April 2019 and April 2021. Otoacoustic Emission (OAE) was used for primary hearing screening 3 days after birth in quiet conditions, and OAE combined with automated auditory brainstem response (AABR) was applied 29-42 days after birth for those who failed or missed the initial screening. Meanwhile, high-throughput sequencing of hotspot HL-associated mutations in GJB2, GJB3, MTRNR1, and SLC26A4 were performed.

RESULTS

Among the 119,606 newborns, 7796 (6.52%) failed the hearing screening. Genetic screening revealed that 5092 neonates (4.26%) carried HL-associated mutations. The detection rate of GJB2, SLC26A4, MTRNR1 and GJB3 mutations were 2.09%, 1.51%, 0.42% and 0.24%, respectively. The most prevalent variant was GJB2 c.235delC (1.74%). The second most prevalent variant was SLC26A4 c.919-2A > G (0.93%). The population who failed the hearing screening had a lower proportion (24.64%) of SLC26A4 gene variants compared to the population who passed (37.46%). Genetic screening identified 4612 (3.86%) carriers who were normal in hearing screenings. The concurrent hearing and genetic screening identified 480 (0.40%) neonates at high risk for hereditary HL.

CONCLUSIONS

The results of this study suggest that the concurrent hearing screening and high-throughput genetic screening would greatly improve the effectiveness of newborn HL programs. This integration also facilitates the management of congenital HL, and aids in the prevention of aminoglycoside antibiotics-induced HL.

Cochlear Health and Cochlear-implant Function

The cochlear implant (CI) is widely considered to be one of the most innovative and successful neuroprosthetic treatments developed to date. Although outcomes vary, CIs are able to effectively improve hearing in nearly all recipients and can substantially improve speech understanding and quality of life for patients with significant hearing loss. A wealth of research has focused on underlying factors that contribute to success with a CI, and recent evidence suggests that the overall health of the cochlea could potentially play a larger role than previously recognized. This article defines and reviews attributes of cochlear health and describes procedures to evaluate cochlear health in humans and animal models in order to examine the effects of cochlear health on performance with a CI. Lastly, we describe how future biologic approaches can be used to preserve and/or enhance cochlear health in order to maximize performance for individual CI recipients.

Precision Medicine Approach to Cochlear Implantation

In the early days of cochlear implantation (CI) surgery, when the types of electrodes were limited and the etiology of sensorineural hearing loss (SNHL) was not well understood, the one-size-fits-all approach to CI held true, as in all other fields. However, in the era of personalized medicine, there have been attempts to associate CI performance with the etiology of SNHL and to establish customized surgical techniques that can maximize performance according to individual cochlear dimensions. Personalized genomic-driven assessments of CI candidates and a better understanding of genotype-phenotype correlations could provide clinically applicable diagnostic and prognostic information about questions such as who, how, and when to implant. Rigorous and strategic imaging assessments also provide better insights into the anatomic etiology of SNHL and cochlear dimensions, leading to individualized surgical techniques to augment CI outcomes. Furthermore, the precision medicine approach to CI is not necessarily limited to preoperative planning, but can be extended to either intraoperative electrode positioning or even the timing of the initial switch-on. In this review, we discuss the implications of personalized diagnoses (both genetic and nongenetic) on the planning and performance of CI in patients with prelingual and postlingual SNHL.

Predictors of Early Language Outcomes in Children with Connexin 26 Hearing Loss across Three Countries

GJB2-associated hearing loss (GJB2-HL) is the most common genetic cause of hearing loss in children. However, little is known about the clinical characteristics and early language outcomes in population-oriented samples including children with different degrees of hearing loss. Insight into these characteristics are relevant for the counselling of parents. Our sample consisted of 66 children at approximately 2 years of age (17–32 months) with bilateral hearing loss due to GJB2 from three population-based cohorts in Austria, Australia and the Netherlands. Predictors of early vocabulary, including demographic, audiological, genetic and intervention variables and the role of medical comorbidities and nonverbal cognition were examined. The vocabulary scores of children with GJB2-HL were approximately 0.7 standard deviations (SDs) below the norms of children with typical hearing. Age at access to family-centered early intervention and first-born position among siblings predicted language outcomes, whereas the degree of hearing loss and genetic subtype were not significantly correlated with expressive vocabulary. In children with GJB2-HL, early access to family-centered early intervention significantly affected language outcomes at the age of two.

The Burden and Benefits of Knowledge: Ethical Considerations Surrounding Population-Based Newborn Genome Screening for Hearing

Recent advances in genomic sequencing technologies have expanded practitioners' utilization of genetic information in a timely and efficient manner for an accurate diagnosis. With an ever-increasing resource of genomic data from progress in the interpretation of genome sequences, clinicians face decisions about how and when genomic information should be presented to families, and at what potential expense. Presently, there is limited knowledge or experience in establishing the value of implementing genome sequencing into newborn screening. Herein we provide insight into the complexities and the burden and benefits of knowledge resulting from genome sequencing of newborns.

[Evaluation of hearing and speech rehabilitation after cochlear implantation in children with Waardenburg syndrome]

Objective:By comparing the hearing and speech rehabilitation effects of cochlear implantation （CI） in children with Waardenburg syndrome （WS） and children with common deafness genes （SLC26A4, GJB2） in the Chinese population, and the hearing and speech rehabilitation effects of bilateral CI and unilateral CI in children with WS, to provide a reference for clinical CIin children with WS. Methods:Follow up and return visit 72 pedestrian cochlear implant children with severe and above sensorineural hearing loss and clear gene mutation type diagnosed by Kunming Children's Hospital from 2017 to 2019, including 24 cases in the WS group, 24 cases in the control group （SLC26A4 deafness group and GJB2 deafness group）. All enrolled children were evaluated for auditory and speech ability 12 months after startup. Results:The hearing aid threshold, the correct recognition rate of speech recognition ability evaluation, IT-MAIS / MAIS score rate, CAP score, SIR score, there was no significant difference（P>0.05）. The correct recognition rates of IT-MAIS / MAIS score, SIR score, natural environment sound recognition, vowel recognition, tone recognition, monosyllabic word recognition, disyllabic word recognition and short sentence recognition in children with WS bilateral CI were significantly higher than those in children with WS unilateral CI （P<0.05）. There was no significant difference in CAP score, initial recognition and correct recognition rate of trisyllabic words between children with WS bilateral CI and children with WS unilateral CI （P>0.05）. Conclusion:Common deafness genes in children with WS and Chinese population （SLC26A4, GJB2） the effect of cochlear implantation on hearing and speech rehabilitation of sick children is equivalent. For children with severe and above sensorineural hearing loss associated with this syndrome, CI can be used clinically to improve their hearing and speech ability. WS bilateral CI has advantages in some hearing and speech abilities compared with unilateral CI, so those whomeet the conditions should be encouraged bilateral implantation.

A Broadly Applicable Method for Characterizing the Slope of the Electrically Evoked Compound Action Potential Amplitude Growth Function

OBJECTIVES

Amplitudes of electrically evoked compound action potentials (eCAPs) as a function of the stimulation level constitute the eCAP amplitude growth function (AGF). The slope of the eCAP AGF (i.e., rate of growth of eCAP amplitude as a function of stimulation level), recorded from subjects with cochlear implants (CIs), has been widely used as an indicator of survival of cochlear nerve fibers. However, substantial variation in the approach used to calculate the slope of the eCAP AGF makes it difficult to compare results across studies. In this study, we developed an improved slope-fitting method by addressing the limitations of previously used approaches and ensuring its application for the estimation of the maximum slopes of the eCAP AGFs recorded in both animal models and human listeners with various etiologies.

DESIGN

The new eCAP AGF fitting method was designed based on sliding window linear regression. Slopes of the eCAP AGF estimated using this new fitting method were calculated and compared with those estimated using four other fitting methods reported in the literature. These four methods were nonlinear regression with a sigmoid function, linear regression, gradient calculation, and boxcar smoothing. The comparison was based on the fitting results of 72 eCAP AGFs recorded from 18 acutely implanted guinea pigs, 46 eCAP AGFs recorded from 23 chronically implanted guinea pigs, and 2094 eCAP AGFs recorded from 200 human CI users from 4 patient populations. The effect of the choice of input units of the eCAP AGF (linear versus logarithmic) on fitting results was also evaluated.

RESULTS

The slope of the eCAP AGF was significantly influenced by the slope-fitting method and by the choice of input units. Overall, slopes estimated using all five fitting methods reflected known patterns of neural survival in human patient populations and were significantly correlated with speech perception scores. However, slopes estimated using the newly developed method showed the highest correlation with spiral ganglion neuron density among all five fitting methods for animal models. In addition, this new method could reliably and accurately estimate the slope for 4 human patient populations, while the performance of the other methods was highly influenced by the morphology of the eCAP AGF.

CONCLUSIONS

The novel slope-fitting method presented in this study addressed the limitations of the other methods reported in the literature and successfully characterized the slope of the eCAP AGF for various animal models and CI patient populations. This method may be useful for researchers in conducting scientific studies and for clinicians in providing clinical care for CI users.

Characteristics of electrically evoked auditory brainstem response in children with large vestibular aqueduct syndrome after cochlear implantation

BACKGROUND

The vestibular aqueduct (VA) width may affect the auditory conduction pathway of large vestibular aqueduct syndrome (LVAS) children.

OBJECTIVE

Analyzing the electrically evoked auditory brainstem response (EABR) after cochlear implantation (CI) in severe to profound sensorineural hearing loss (SNHL) children with LVAS.

MATERIALS AND METHODS

Fifty-four children with SNHL who received CI were selected, including 21 children with LVAS and 33 children without inner ear malformations (IEMs). The VA width was measured in LVAS children. The post-operative EABRs were recorded in all children.

RESULTS

For the LVAS group, the VA width was positively correlated with wave III (eIII) latency of EABR at the No. 2 electrode (E2), E5, E8, and E11, the VA width was positively correlated with wave V (eV) latency of EABR at E2, E5, E8, and E11. Only the eV latency of E2 showed a significant difference between the two groups.

CONCLUSION AND SIGNIFICANCE

SNHL children with LVAS and no IEMs have similar conduction of the auditory pathway. In the LVAS group, the conduction of the auditory pathway becomes better with the decrease of VA width. Rational use of post-operative EABRs and the measurement of anatomical parameters can effectively assess the development of part auditory pathways in LVAS children, which may be helpful in predicting post-operative speech and hearing recovery.

Genetics of Childhood Hearing Loss

Compelling evidence indicates that some newborns harboring genetic variants associated with hearing loss might not be identified by current physiologic newborn hearing screening (NBHS) rendering current NBHS protocols suboptimal. Incorporating genomic sequencing into NBHS would improve clinical diagnosis and decrease time to early intervention efforts.

Outcomes of Cochlear Implantation in Patients with Pendred syndrome: A Systematic Review and Narrative Synthesis

Establish outcomes following cochlear implantation (CI) in patients with Pendred syndrome. Systematic review and narrative synthesis. Databases searched: Medline, Pubmed, Embase, Web of Science, Cochrane Collection and ClinicalTrials.gov. No limits placed on language or year of publication. Review conducted in accordance with the PRISMA statement. Searches identified 251 abstracts and 242 full texts. Of these, 22 studies met inclusion criteria reporting outcomes in 231 patients with at least 234 implants. Hearing outcomes were generally good with patients experiencing useful functional improvement. A total of 46 minor complications were reported in 78 cases. The methodological quality of included studies was modest, predominantly consisting of case reports and non-controlled case series with small numbers of patients. All studies were OCEBM grade III-IV. Hearing outcomes following CI in Pendred syndrome are generally good with useful functional improvement. However, outcomes reported in published studies lack long term follow up.

The Effects of GJB2 or SLC26A4 Gene Mutations on Neural Response of the Electrically Stimulated Auditory Nerve in Children

OBJECTIVES

This study aimed to (1) investigate the effect of GJB2 and SLC26A4 gene mutations on auditory nerve function in pediatric cochlear implant users and (2) compare their results with those measured in implanted children with idiopathic hearing loss.

DESIGN

Participants included 20 children with biallelic GJB2 mutations, 16 children with biallelic SLC26A4 mutations, and 19 children with idiopathic hearing loss. All subjects except for two in the SLC26A4 group had concurrent Mondini malformation and enlarged vestibular aqueduct. All subjects used Cochlear Nucleus devices in their test ears. For each subject, electrophysiological measures of the electrically evoked compound action potential (eCAP) were recorded using both anodic- and cathodic-leading biphasic pulses. Dependent variables (DVs) of interest included slope of eCAP input/output (I/O) function, the eCAP threshold, and eCAP amplitude measured at the maximum comfortable level (C level) of the anodic-leading stimulus (i.e., the anodic C level). Slopes of eCAP I/O functions were estimated using statistical modeling with a linear regression function. These DVs were measured at three electrode locations across the electrode array. Generalized linear mixed effect models were used to evaluate the effects of study group, stimulus polarity, and electrode location on each DV.

RESULTS

Steeper slopes of eCAP I/O function, lower eCAP thresholds, and larger eCAP amplitude at the anodic C level were measured for the anodic-leading stimulus compared with the cathodic-leading stimulus in all subject groups. Children with GJB2 mutations showed steeper slopes of eCAP I/O function and larger eCAP amplitudes at the anodic C level than children with SLC26A4 mutations and children with idiopathic hearing loss for both the anodic- and cathodic-leading stimuli. In addition, children with GJB2 mutations showed a smaller increase in eCAP amplitude when the stimulus changed from the cathodic-leading pulse to the anodic-leading pulse (i.e., smaller polarity effect) than children with idiopathic hearing loss. There was no statistically significant difference in slope of eCAP I/O function, eCAP amplitude at the anodic C level, or the size of polarity effect on all three DVs between children with SLC26A4 mutations and children with idiopathic hearing loss. These results suggested that better auditory nerve function was associated with GJB2 but not with SLC26A4 mutations when compared with idiopathic hearing loss. In addition, significant effects of electrode location were observed for slope of eCAP I/O function and the eCAP threshold.

CONCLUSIONS

GJB2 and SLC26A4 gene mutations did not alter polarity sensitivity of auditory nerve fibers to electrical stimulation. The anodic-leading stimulus was generally more effective in activating auditory nerve fibers than the cathodic-leading stimulus, despite the presence of GJB2 or SLC26A4 mutations. Patients with GJB2 mutations appeared to have better functional status of the auditory nerve than patients with SLC26A4 mutations who had concurrent Mondini malformation and enlarged vestibular aqueduct and patients with idiopathic hearing loss.

Prelinguistic Vocal Development in Children With Cochlear Implants: A Systematic Review

OBJECTIVES

This systematic review is designed to (a) describe measures used to quantify vocal development in pediatric cochlear implant (CI) users, (b) synthesize the evidence on prelinguistic vocal development in young children before and after cochlear implantation, and (c) analyze the application of the current evidence for evaluating change in vocal development before and after cochlear implantation for young children. Investigations of prelinguistic vocal development after cochlear implantation are only beginning to uncover the expected course of prelinguistic vocal development in children with CIs and what factors influence that course, which varies substantially across pediatric CI users. A deeper understanding of prelinguistic vocal development will improve professionals' abilities to determine whether a child with a CI is exhibiting sufficient progress soon after implantation and to adjust intervention as needed.

DESIGN

We systematically searched PubMed, ProQuest, and CINAHL databases for primary reports of children who received a CI before 5 years 0 months of age that included at least one measure of nonword, nonvegetative vocalizations. We also completed supplementary searches.

RESULTS

Of the 1916 identified records, 59 met inclusion criteria. The included records included 1125 total participants, which came from 36 unique samples. Records included a median of 8 participants and rarely included children with disabilities other than hearing loss. Nearly all of the records met criteria for level 3 for quality of evidence on a scale of 1 (highest) to 4 (lowest). Records utilized a wide variety of vocalization measures but often incorporated features related to canonical babbling. The limited evidence from pediatric CI candidates before implantation suggests that they are likely to exhibit deficits in canonical syllables, a critical vocal development skill, and phonetic inventory size. Following cochlear implantation, multiple studies report similar patterns of growth, but faster rates producing canonical syllables in children with CIs than peers with comparable durations of robust hearing. However, caution is warranted because these demonstrated vocal development skills still occur at older chronological ages for children with CIs than chronological age peers with typical hearing.

CONCLUSIONS

Despite including a relatively large number of records, the evidence in this review regarding changes in vocal development before and after cochlear implantation in young children remains limited. A deeper understanding of when prelinguistic skills are expected to develop, factors that explain deviation from that course, and the long-term impacts of variations in vocal prelinguistic development is needed. The diverse and dynamic nature of the relatively small population of pediatric CI users as well as relatively new vocal development measures present challenges for documenting and predicting vocal development in pediatric CI users before and after cochlear implantation. Synthesizing results across multiple institutions and completing rigorous studies with theoretically motivated, falsifiable research questions will address a number of challenges for understanding prelinguistic vocal development in children with CIs and its relations with other current and future skills. Clinical implications include the need to measure prelinguistic vocalizations regularly and systematically to inform intervention planning.

Future directions for screening and treatment in congenital hearing loss

Hearing loss is the most common neurosensory deficit. It results from a variety of heritable and acquired causes and is linked to multiple deleterious effects on a child's development that can be ameliorated by prompt identification and individualized therapies. Diagnosing hearing loss in newborns is challenging, especially in mild or progressive cases, and its management requires a multidisciplinary team of healthcare providers comprising audiologists, pediatricians, otolaryngologists, and genetic counselors. While physiologic newborn hearing screening has resulted in earlier diagnosis of hearing loss than ever before, a growing body of knowledge supports the concurrent implementation of genetic and cytomegalovirus testing to offset the limitations inherent to a singular screening modality. In this review, we discuss the contemporary role of screening for hearing loss in newborns as well as future directions in its diagnosis and treatment.

A novel SLC26A4 splicing mutation identified in two deaf Chinese twin sisters with enlarged vestibular aqueducts

Background

Variants in the SLC26A4 gene are correlated with nonsyndromic hearing loss with an enlarged vestibular aqueduct (EVA). This study aimed to identify the genetic causes in a Chinese family with EVA, and the pathogenicity of the detected variants.

Methods

We collected blood samples and clinical data from a pair of deaf twin sisters with EVA and their family members. As controls, a group of 500 normal‐hearing people were enrolled in our study. Twenty‐one exons and flanking splice sites of the SLC26A4 gene were screened for pathogenic mutations by polymerase chain reaction and bidirectional Sanger sequencing. Minigene assays were used to verify whether the novel SLC26A4 intronic mutation influenced the normal splicing of mRNA.

Results

Hearing loss in the twins with EVA was diagnosed using auditory tests and imaging examinations. Two pathogenic mutations, c.919‐2A>G and c.1614+5G>A were detected in SLC26A4, the latter of which has not been reported in the literature. The minigene expression in vitro confirmed that c.1614+5G>A could cause aberrant splicing, resulting in skipping over exon 14.

Conclusions

On the SLC26A4 gene, c.1614+5G>A is a pathogenic mutation. This finding enriches the mutational spectrum of the SLC26A4 gene and provides a basis for the genetic diagnosis of EVA.

Genotype-Phenotype Correlation for Predicting Cochlear Implant Outcome: Current Challenges and Opportunities

The use and utility of cochlear implantation has rapidly increased in recent years as technological advances in the field have expanded both the efficacy and eligible patient population for implantation. This review aims to serve as a general overview of the most common hearing disorders that have favorable auditory outcomes with cochlear implants (CI). Hearing loss in children caused by congenital cytomegalovirus infection, syndromic conditions including Pendred Syndrome, and non-syndromic genetic conditions such as hearing impairment associated with GJB2 mutations have shown to be successfully managed by CI. Furthermore, cochlear implantation provides the auditory rehabilitation for the most common etiology of hearing loss in adults and age-related hearing loss (ARHL) or presbycusis. However, in some cases, cochlear implantation have been associated with some challenges. Regarding implantation in children, studies have shown that sometimes parents seem to have unrealistic expectations regarding the ability of CI to provide auditory rehabilitation and speech improvement. Given the evidence revealing the beneficial effects of early intervention via CI in individuals with hearing disorders especially hearing loss due to genetic etiology, early auditory and genetic screening efforts may yield better clinical outcomes. There is a need to better understand genotype-phenotype correlations and CI outcome, so that effective genetic counseling and successful treatment strategies can be developed at the appropriate time for hearing impaired individuals.

Auditory Detection Thresholds and Cochlear Resistivity Differ Between Pediatric Cochlear Implant Listeners With Enlarged Vestibular Aqueduct and Those With Connexin-26 Mutations

Purpose The goal of this study was to evaluate differences in the electrode-neuron interface as a function of hearing loss etiology in pediatric cochlear implant (CI) listeners with enlarged vestibular aqueduct (EVA) syndrome and in those with autosomal recessive connexin-26 mutations (DFNB1). Method Fifteen implanted ears (9 participants, 5 ears with EVA, 10 ears with DFNB1) were assessed. Single-channel auditory detection thresholds were measured using broad and spatially focused electrode configurations (steered quadrupolar; focusing coefficients = 0 and 0.9). Cochlear resistivity estimates were obtained via electrode impedances and electrical field imaging. Between-group differences were evaluated using linear mixed-effects models. Results Children with EVA had significantly higher auditory detection thresholds than children with DFNB1, irrespective of electrode configuration. Between-group differences in thresholds were more pronounced on apical electrodes than on basal electrodes. In the apex, electrode impedances and electrical field imaging values were higher for children with EVA than for those with DFNB1. Conclusions The electrode-neuron interface differs between pediatric CI listeners with DFNB1 and those with EVA. It is possible that optimal clinical interventions may depend, in part, on hearing loss etiology. Future investigations with large samples should investigate individualized CI programming strategies for listeners with EVA and DFNB1.

Concurrent Hearing and Genetic Screening of 180,469 Neonates with Follow-up in Beijing, China

Concurrent hearing and genetic screening of newborns is expected to play important roles not only in early detection and diagnosis of congenital deafness, which triggers intervention, but also in predicting late-onset and progressive hearing loss and identifying individuals who are at risk of drug-induced HL. Concurrent hearing and genetic screening in the whole newborn population in Beijing was launched in January 2012. This study included 180,469 infants born in Beijing between April 2013 and March 2014, with last follow-up on February 24, 2018. Hearing screening was performed using transiently evoked otoacoustic emission (TEOAE) and automated auditory brainstem response (AABR). For genetic testing, dried blood spots were collected and nine variants in four genes, GJB2, SLC26A4, mtDNA 12S rRNA, and GJB3, were screened using a DNA microarray platform. Of the 180,469 infants, 1,915 (1.061%) were referred bilaterally or unilaterally for hearing screening; 8,136 (4.508%) were positive for genetic screening (heterozygote, homozygote, or compound heterozygote and mtDNA homoplasmy or heteroplasmy), among whom 7,896 (4.375%) passed hearing screening. Forty (0.022%) infants carried two variants in GJB2 or SLC26A4 (homozygote or compound heterozygote) and 10 of those infants passed newborn hearing screening. In total, 409 (0.227%) infants carried the mtDNA 12S rRNA variant (m.1555A>G or m.1494C>T), and 405 of them passed newborn hearing screening. In this cohort study, 25% of infants with pathogenic combinations of GJB2 or SLC26A4 variants and 99% of infants with an m.1555A>G or m.1494C>T variant passed routine newborn hearing screening, indicating that concurrent screening provides a more comprehensive approach for management of congenital deafness and prevention of ototoxicity.

Outcome of Cochlear Implantation in Prelingually Deafened Children According to Molecular Genetic Etiology

OBJECTIVES

About 60% of Korean pediatric cochlear implantees could be genetically diagnosed (GD) and we previously reported that a substantial portion of undiagnosed cases by deafness gene panel sequencing were predicted to have a nongenetic or complex etiology. We aimed to compare the outcomes of cochlear implantation (CI) in GD and genetically undiagnosed (GUD) patients and attempted to determine CI outcomes according to etiology.

DESIGN

Ninety-three pediatric cochlear implantees underwent molecular genetic testing. Fifty-seven patients carried pathogenic variants and 36 patients remained GUD after panel sequencing of 204 known or potential deafness genes (TRS-204). Among them, 55 cochlear implantees with reliable speech evaluation results with a follow-up of longer than 24 months were recruited. Longitudinal changes in the audiologic performance were compared between the GD (n = 31) and GUD (n = 24) groups. The GD group was subdivided into cochlear implantee with SLC26A4 mutations (group 1) and cochlear implantee with other genetic etiology (group 2), and the GUD group was subdivided into groups 3 and 4, that is, patients with or without inner ear anomaly, respectively.

RESULTS

Group 1 related to SLC26A4 mutations had the highest categories of auditory perception scores among all groups pre- and postoperatively. Group 4 with inner ear anomaly had the lowest categories of auditory perception scores. At 24 months post-CI, the group 2 with another genetic etiology had significantly better outcomes than molecularly undiagnosed group 3, which had with the same condition as group 2 except that the candidate gene was not detected. This finding was recapitulated when we limited cases to those that underwent CI before 24 months of age to minimize age-related bias at implantation. Furthermore, on extending the follow-up to 36 months postoperatively, this tendency became more prominent. Additionally, our preliminary clinical data suggest a narrower sensitive window period for good CI outcomes for implantees with OTOF mutation rather than the GJB2 and other genes.

CONCLUSIONS

Current molecular genetic testing including deafness panel sequencing helps to predict the 2-year follow-up outcomes after CI in prelingually deafened children. GD cochlear implantees show better functional outcomes after CI than undiagnosed cochlear implantees as determined by deafness panel sequencing, suggesting a genotype-functional outcome correlation. The genetic testing may provide a customized optimal window period in terms of CI timing for favorable outcome according to genetic etiology.

Precision medicine in hearing loss

Precision medicine (PM) proposes customized medical care based on a patient's unique genome, biomarkers, environment and behaviors. Hearing loss (HL) is the most common sensorineural disorder worldwide and is frequently caused by a single genetic mutation. With recent advances in PM tools such as genetic sequencing and data analysis, the field of HL is ideally positioned to adopt the strategies of PM. Here, we review current and future applications of PM in HL as they relate to the four core qualities of PM (P4): predictive, personalized, patient-centered, and participatory. We then introduce a strategy for effective incorporation of HL PM into the design of future research studies, electronic medical records, and clinical practice to improve diagnostics, prognostics, and, ultimately, individualized patient treatment. Finally, specific anticipated ethical and economic concerns in this growing era of genomics-based HL treatment are discussed. By integrating PM principles into translational HL research and clinical practice, hearing specialists are uniquely positioned to effectively treat the heterogeneous causes and manifestations of HL on an individualized basis.

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

BACKGROUND AND OBJECTIVES

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

SUBJECTS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Outcomes of cochlear implantation for the patients with specific genetic etiologies: a systematic literature review

CONCLUSION

Most of the cases with gene mutations of intra-cochlear etiology showed relatively good CI outcomes. To progress toward more solid evidence-based CI intervention, a greater number of reports including CI outcomes for specific gene mutations are desired.

BACKGROUND

Cochlear implantation (CI) is the most important and effective treatment for patients with profound sensorineural hearing loss. However, the outcomes of CI vary among patients. One of the reasons of this heterogeneous outcome for cochlear implantation is thought to be the heterogeneous nature of hearing loss. Indeed, genetic factors, the most common etiology in severe-to-profound hearing loss, might be one of the key determinants of outcomes for CI and electric acoustic stimulation (EAS). Patients with genetic causes involving an 'intra-cochlear' etiology show good CI/EAS outcomes.

REVIEW

This review article aimed to summarize the reports on CI/EAS outcomes in patients with special genetic causes as well as to assist in future clinical decision-making. Most of the cases were suspected of an intra-cochlear etiology, such as those with GJB2, SLC26A4, and OTOF mutations, which showed relatively good CI outcomes. However, there have only been a limited number of reports on patients with other gene mutations.

Genetic Predisposition to Sporadic Congenital Hearing Loss in a Pediatric Population

Discriminating between inherited and non-inherited sporadic hearing loss is challenging. Here, we attempted to delineate genetic inheritance in simplex cases of severe-to-profound congenital hearing loss in Korean children. Variations in SLC26A4 and GJB2 in 28 children with bilateral severe-to-profound non-syndromic hearing loss (NSHL) without familial history were analyzed using Sanger sequencing. Genetic analysis of individuals without mutations in SLC26A4 and GJB2 was performed by whole exome sequencing (WES). Bi-allelic mutations in SLC26A4 and GJB2 were identified in 12 and 3 subjects, respectively. Of the 13 individuals without mutations in SLC26A4 and GJB2, 2 and 1 carried compound heterozygous mutations in MYO15A and CDH23, respectively. Thus, 64.3% (18/28) of individuals with NSHL were determined to be genetically predisposed. Individuals with sporadic severe-to-profound NSHL were found to mostly exhibit an autosomal recessive inheritance pattern. Novel causative candidate genes for NSHL were identified by analysis of WES data of 10 families without mutations in known causative genes. Bi-allelic mutations predisposing to NSHL were identified in 64.3% of subjects with sporadic severe-to-profound NSHL. Given that several causative genes for NSHL are still unidentified, genetic inheritance of sporadic congenital hearing loss could be more common than that indicated by our results.

Intelligence development of pre-lingual deaf children with unilateral cochlear implantation

OBJECTIVE

The present study aims to test whether deaf children with unilateral cochlear implantation (CI) have higher intelligence quotients (IQ). We also try to find out the predictive factors of intelligence development in deaf children with CI.

METHODS

Totally, 186 children were enrolled into this study. They were divided into 3 groups: CI group (N = 66), hearing loss group (N = 54) and normal hearing group (N = 66). All children took the Hiskey-Nebraska Test of Learning Aptitude to assess the IQ. After that, we used Deafness gene chip, Categories of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) methods to evaluate the genotype, auditory and speech performance, respectively.

RESULTS

At baseline, the average IQ of hearing loss group (HL), CI group, normal hearing (NH) group were 98.3 ± 9.23, 100.03 ± 12.13 and 109.89 ± 10.56, while NH group scored higher significantly than HL and CI groups (p < 0.05). After 12 months, the average IQ of HL group, CI group, NH group were99.54 ± 9.38,111.85 ± 15.38, and 112.08 ± 8.51, respectively. No significant difference between the IQ of the CI and NH groups was found (p > 0.05). The growth of SIR was positive correlated with the growth of IQ (r = 0.247, p = 0.046), while no significant correlation were found between IQ growth and other possible factors, i.e. gender, age of CI, use of hearing aid, genotype, implant device type, inner ear malformation and CAP growth (p > 0.05).

CONCLUSIONS

Our study suggests that CI potentially improves the intelligence development in deaf children. Speech performance growth is significantly correlated with IQ growth of CI children. Deaf children accepted CI before 6 years can achieve a satisfying and undifferentiated short-term (12 months) development of intelligence.

A Comprehensive Study on the Etiology of Patients Receiving Cochlear Implantation With Special Emphasis on Genetic Epidemiology

Objective:

Cochlear implantation is the most important treatment currently available for profound sensorineural hearing loss. The aim of this study was to investigate the etiology of hearing loss in patients with cochlear implantation, and to compare outcomes.

Methods:

Japanese hearing loss patients who received cochlear implants (CIs) or electric acoustic stimulation (EAS) in Shinshu University hospital (n = 173, prelingual onset: 92, postlingual onset: 81) participated in this study. Invader assay followed by the targeted exon-sequencing of 63 deafness genes using Massively parallel DNA sequencing (MPS) was applied. For prelingual patients, additional imaging examination, cCMV screening, and pediatric examination were performed for precise diagnosis.

Results:

Genetic screening successfully identified the causative mutation in 60% of patients with prelingual onset hearing loss and in 36% of those with postlingual hearing loss. Differences in the kinds of genes identified were observed between the two groups. Although there were marked variations in the outcome of cochlear implantation, patients with specific deafness gene mutations showed relatively good results.

Conclusion:

The present study showed genetic etiology is a major cause of hearing loss in CI/EAS patients. Patients possessing mutations in a number of deafness genes known to be expressed within inner ear have achieved satisfactory auditory performance, suggesting that the identification of the genetic background facilitates the prediction of post-CI performance. MPS is a powerful tool for the identification of causative deafness genes in patients receiving cochlear implantation. Therefore, determination of the involved region inside/outside of the cochlea by identification of the responsible gene is essential.

Long-Term Cochlear Implant Outcomes in Children with GJB2 and SLC26A4 Mutations

Objectives

To investigate speech and language outcomes in children with cochlear implants (CIs) who had mutations in common deafness genes and to compare their performances with those without mutations.

Study Design

Prospective study.

Methods

Patients who received CIs before 18 years of age and had used CIs for more than 3 years were enrolled in this study. All patients underwent mutation screening of three common deafness genes: GJB2, SLC26A4 and the mitochondrial 12S rRNA gene. The outcomes with CIs were assessed at post-implant years 3 and 5 using the Categories of Auditory Performance (CAP) scale, Speech Intelligibility Rating (SIR) scale, speech perception tests and language skill tests.

Results

Forty-eight patients were found to have confirmative mutations in GJB2 or SLC26A4, and 123 without detected mutations were ascertained for comparison. Among children who received CIs before 3.5 years of age, patients with GJB2 or SLC26A4 mutations showed significantly higher CAP/SIR scores than those without mutations at post-implant year 3 (p = 0.001 for CAP; p = 0.004 for SIR) and year 5 (p = 0.035 for CAP; p = 0.038 for SIR). By contrast, among children who received CIs after age 3.5, no significant differences were noted in post-implant outcomes between patients with and without mutations (all p > 0.05).

Conclusion

GJB2 and SLC26A4 mutations are associated with good post-implant outcomes. However, their effects on CI outcomes may be modulated by the age at implantation: the association between mutations and CI outcomes is observed in young recipients who received CIs before age 3.5 years but not in older recipients.

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

CONCLUSIONS

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

OBJECTIVE

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

METHODS

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

RESULTS

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