Stable long-term outcomes after cochlear implantation in subjects with TMPRSS3 associated hearing loss: a retrospective multicentre study

BACKGROUND

The spiral ganglion hypothesis suggests that pathogenic variants in genes preferentially expressed in the spiral ganglion nerves (SGN), may lead to poor cochlear implant (CI) performance. It was long thought that TMPRSS3 was particularly expressed in the SGNs. However, this is not in line with recent reviews evaluating CI performance in subjects with TMPRSS3-associated sensorineural hearing loss (SNHL) reporting overall beneficial outcomes. These outcomes are, however, based on variable follow-up times of, in general, 1 year or less. Therefore, we aimed to 1. evaluate long-term outcomes after CI implantation of speech recognition in quiet in subjects with TMPRSS3-associated SNHL, and 2. test the spiral ganglion hypothesis using the TMPRSS3-group.

METHODS

This retrospective, multicentre study evaluated long-term CI performance in a Dutch population with TMPRSS3-associated SNHL. The phoneme scores at 70 dB with CI in the TMPRSS3-group were compared to a control group of fully genotyped cochlear implant users with post-lingual SNHL without genes affecting the SGN, or severe anatomical inner ear malformations. CI-recipients with a phoneme score ≤ 70% at least 1-year post-implantation were considered poor performers and were evaluated in more detail.

RESULTS

The TMPRSS3 group consisted of 29 subjects (N = 33 ears), and the control group of 62 subjects (N = 67 ears). For the TMPRSS3-group, we found an average phoneme score of 89% after 5 years, which remained stable up to 10 years post-implantation. At both 5 and 10-year follow-up, no difference was found in speech recognition in quiet between both groups (p = 0.830 and p = 0.987, respectively). Despite these overall adequate CI outcomes, six CI recipients had a phoneme score of ≤ 70% and were considered poor performers. The latter was observed in subjects with residual hearing post-implantation or older age at implantation.

CONCLUSION

Subjects with TMPRSS3-associated SNHL have adequate and stable long-term outcomes after cochlear implantation, equal to the performance of genotyped patient with affected genes not expressed in the SGN. These findings are not in line with the spiral ganglion hypothesis. However, more recent studies showed that TMPRSS3 is mainly expressed in the hair cells with only limited SGN expression. Therefore, we cannot confirm nor refute the spiral ganglion hypothesis.

Variability in Cochlear Implantation Outcomes in a Large German Cohort With a Genetic Etiology of Hearing Loss

OBJECTIVES

The variability in outcomes of cochlear implantation is largely unexplained, and clinical factors are not sufficient for predicting performance. Genetic factors have been suggested to impact outcomes, but the clinical and genetic heterogeneity of hereditary hearing loss makes it difficult to determine and interpret postoperative performance. It is hypothesized that genetic mutations that affect the neuronal components of the cochlea and auditory pathway, targeted by the cochlear implant (CI), may lead to poor performance. A large cohort of CI recipients was studied to verify this hypothesis.

DESIGN

This study included a large German cohort of CI recipients (n = 123 implanted ears; n = 76 probands) with a definitive genetic etiology of hearing loss according to the American College of Medical Genetics (ACMG)/Association for Molecular Pathology (AMP) guidelines and documented postoperative audiological outcomes. All patients underwent preoperative clinical and audiological examinations. Postoperative CI outcome measures were based on at least 1 year of postoperative audiological follow-up for patients with postlingual hearing loss onset (>6 years) and 5 years for children with congenital or pre/perilingual hearing loss onset (≤6 years). Genetic analysis was performed based on three different methods that included single-gene screening, custom-designed hearing loss gene panel sequencing, targeting known syndromic and nonsyndromic hearing loss genes, and whole-genome sequencing.

RESULTS

The genetic diagnosis of the 76 probands in the genetic cohort involved 35 genes and 61 different clinically relevant (pathogenic, likely pathogenic) variants. With regard to implanted ears (n = 123), the six most frequently affected genes affecting nearly one-half of implanted ears were GJB2 (21%; n = 26), TMPRSS3 (7%; n = 9), MYO15A (7%; n = 8), SLC26A4 (5%; n = 6), and LOXHD1 and USH2A (each 4%; n = 5). CI recipients with pathogenic variants that influence the sensory nonneural structures performed at or above the median level of speech performance of all ears at 70% [monosyllable word recognition score in quiet at 65 decibels sound pressure level (SPL)]. When gene expression categories were compared to demographic and clinical categories (total number of compared categories: n = 30), mutations in genes expressed in the spiral ganglion emerged as a significant factor more negatively affecting cochlear implantation outcomes than all clinical parameters. An ANOVA of a reduced set of genetic and clinical categories (n = 10) identified five detrimental factors leading to poorer performance with highly significant effects ( p < 0.001), accounting for a total of 11.8% of the observed variance. The single strongest category was neural gene expression accounting for 3.1% of the variance.

CONCLUSIONS

The analysis of the relationship between the molecular genetic diagnoses of a hereditary etiology of hearing loss and cochlear implantation outcomes in a large German cohort of CI recipients revealed significant variabilities. Poor performance was observed with genetic mutations that affected the neural components of the cochlea, supporting the "spiral ganglion hypothesis."

Rescue of auditory function by a single administration of AAV-TMPRSS3 gene therapy in aged mice of human recessive deafness DFNB8

Patients with mutations in the TMPRSS3 gene suffer from recessive deafness DFNB8/DFNB10. For these patients, cochlear implantation is the only treatment option. Poor cochlear implantation outcomes are seen in some patients. To develop biological treatment for TMPRSS3 patients, we generated a knockin mouse model with a frequent human DFNB8 TMPRSS3 mutation. The Tmprss3A306T/A306T homozygous mice display delayed onset progressive hearing loss similar to human DFNB8 patients. Using AAV2 as a vector to carry a human TMPRSS3 gene, AAV2-hTMPRSS3 injection in the adult knockin mouse inner ear results in TMPRSS3 expression in the hair cells and the spiral ganglion neurons. A single AAV2-hTMPRSS3 injection in Tmprss3A306T/A306T mice of an average age of 18.5 months leads to sustained rescue of the auditory function to a level similar to wild-type mice. AAV2-hTMPRSS3 delivery rescues the hair cells and the spiral ganglions neurons. This study demonstrates successful gene therapy in an aged mouse model of human genetic deafness. It lays the foundation to develop AAV2-hTMPRSS3 gene therapy to treat DFNB8 patients, as a standalone therapy or in combination with cochlear implantation.

Genotype-Phenotype Correlations in TMPRSS3 (DFNB10/DFNB8) with Emphasis on Natural History

BACKGROUND

Mutations in TMPRSS3 are an important cause of autosomal recessive non-syndromic hearing loss. The hearing loss associated with mutations in TMPRSS3 is characterized by phenotypic heterogeneity, ranging from mild to profound hearing loss, and is generally progressive. Clinical presentation and natural history of TMPRSS3 mutations vary significantly based on the location and type of mutation in the gene. Understanding these genotype-phenotype relationships and associated natural disease histories is necessary for the successful development and application of gene-based therapies and precision medicine approaches to DFNB8/10. The heterogeneous presentation of TMPRSS3-associated disease makes it difficult to identify patients clinically. As the body of literature on TMPRSS3-associated deafness grows, there is need for better categorization of the hearing phenotypes associated with specific mutations in the gene.

SUMMARY

In this review, we summarize TMPRSS3 genotype-phenotype relationships including a thorough description of the natural history of patients with TMPRSS3-associated hearing loss to lay the groundwork for the future of TMPRSS3 treatment using molecular therapy.

KEY MESSAGES

TMPRSS3 mutation is a significant cause of genetic hearing loss. All patients with TMPRSS3 mutation display severe-to-profound prelingual (DFNB10) or a postlingual (DFNB8) progressive sensorineural hearing loss. Importantly, TMPRSS3 mutations have not been associated with middle ear or vestibular deficits. The c.916G>A (p.Ala306Thr) missense mutation is the most frequently reported mutation across populations and should be further explored as a target for molecular therapy.

Structural analysis of pathogenic TMPRSS3 variants and their cochlear implantation outcomes of sensorineural hearing loss

TMPRSS3, a type II transmembrane serine protease, is involved in various biological processes including the development and maintenance of the inner ear. Biallelic variants in TMPRSS3 typically result in altered protease activity, causing autosomal recessive non-syndromic hearing loss (ARNSHL). Structural modeling has been conducted to predict the pathogenicity of TMPRSS3 variants and to gain a better understanding of their prognostic correlation. The mutant-driven changes in TMPRSS3 had substantial impacts on neighboring residues, and the pathogenicity of variants was predicted based on their distance from the active site. However, a more in-depth analysis of other factors, such as intramolecular interactions and protein stability, which affect proteolytic activities is yet to be conducted for TMPRSS3 variants. Among 620 probands who provided genomic DNA for molecular genetic testing, eight families with biallelic TMPRSS3 variants that were segregated in a trans configuration were included. Seven different mutant alleles, either homozygous or compound heterozygous, contributed to TMPRSS3-associated ARNSHL, expanding the genotypic spectrum of disease-causing TMPRSS3 variants. Through three-dimensional modeling and structural analysis, TMPRSS3 variants compromise protein stability by altering intramolecular interactions, and each mutant differently interacts with the serine protease active site. Furthermore, the changes in intramolecular interactions leading to regional instability correlate with the results of functional assay and residual hearing function, but overall stability predictions do not. Our findings also build on previous evidence indicating that most recipients with TMPRSS3 variants have favorable cochlear implantation (CI) outcomes. We found that age at CI was significantly correlated with speech performance outcomes; genotype was not correlated with these outcomes. Collectively, the results of this study contribute to a more structural understanding of the underlying mechanisms of ARNSHL caused by TMPRSS3 variants.

Association of Genetic Diagnoses for Childhood-Onset Hearing Loss With Cochlear Implant Outcomes

Importance

In the US, most childhood-onset bilateral sensorineural hearing loss is genetic, with more than 120 genes and thousands of different alleles known. Primary treatments are hearing aids and cochlear implants. Genetic diagnosis can inform progression of hearing loss, indicate potential syndromic features, and suggest best timing for individualized treatment.

Objective

To identify the genetic causes of childhood-onset hearing loss and characterize severity, progression, and cochlear implant success associated with genotype in a single large clinical cohort.

Design, Setting, and Participants

This cross-sectional analysis (genomics) and retrospective cohort analysis (audiological measures) were conducted from 2019 to 2022 at the otolaryngology and audiology clinics of Seattle Children's Hospital and the University of Washington and included 449 children from 406 families with bilateral sensorineural hearing loss with an onset younger than 18 years. Data were analyzed between January and June 2022.

Main Outcomes and Measures

Genetic diagnoses based on genomic sequencing and structural variant analysis of the DNA of participants; severity and progression of hearing loss as measured by audiologic testing; and cochlear implant success as measured by pediatric and adult speech perception tests. Hearing thresholds and speech perception scores were evaluated with respect to age at implant, months since implant, and genotype using a multivariate analysis of variance and covariance.

Results

Of 406 participants, 208 (51%) were female, 17 (4%) were African/African American, 32 (8%) were East Asian, 219 (54%) were European, 53 (13%) were Latino/Admixed American, and 16 (4%) were South Asian. Genomic analysis yielded genetic diagnoses for 210 of 406 families (52%), including 55 of 82 multiplex families (67%) and 155 of 324 singleton families (48%). Rates of genetic diagnosis were similar for children of all ancestries. Causal variants occurred in 43 different genes, with each child (with 1 exception) having causative variant(s) in only 1 gene. Hearing loss severity, affected frequencies, and progression varied by gene and, for some genes, by genotype within gene. For children with causative mutations in MYO6, OTOA, SLC26A4, TMPRSS3, or severe loss-of-function variants in GJB2, hearing loss was progressive, with losses of more than 10 dB per decade. For all children with cochlear implants, outcomes of adult speech perception tests were greater than preimplanted levels. Yet the degree of success varied substantially by genotype. Adjusting for age at implant and interval since implant, speech perception was highest for children with hearing loss due to MITF or TMPRSS3.

Conclusions and Relevance

The results of this cross-sectional study suggest that genetic diagnosis is now sufficiently advanced to enable its integration into precision medical care for childhood-onset hearing loss.

TMPRSS3 expression is limited in spiral ganglion neurons: implication for successful cochlear implantation

BACKGROUND

It is well established that biallelic mutations in transmembrane protease, serine 3 (TMPRSS3) cause hearing loss. Currently, there is controversy regarding the audiological outcomes after cochlear implantation (CI) for TMPRSS3-associated hearing loss. This controversy creates confusion among healthcare providers regarding the best treatment options for individuals with TMPRSS3-related hearing loss.

METHODS

A literature review was performed to identify all published cases of patients with TMPRSS3-associated hearing loss who received a CI. CI outcomes of this cohort were compared with published adult CI cohorts using postoperative consonant-nucleus-consonant (CNC) word performance. TMPRSS3 expression in mouse cochlea and human auditory nerves (HAN) was determined by using hybridisation chain reaction and single-cell RNA-sequencing analysis.

RESULTS

In aggregate, 27 patients (30 total CI ears) with TMPRSS3-associated hearing loss treated with CI, and 85% of patients reported favourable outcomes. Postoperative CNC word scores in patients with TMPRSS3-associated hearing loss were not significantly different than those seen in adult CI cohorts (8 studies). Robust Tmprss3 expression occurs throughout the mouse organ of Corti, the spindle and root cells of the lateral wall and faint staining within <5% of the HAN, representing type II spiral ganglion neurons. Adult HAN express negligible levels of TMPRSS3.

CONCLUSION

The clinical features after CI and physiological expression of TMPRSS3 suggest against a major role of TMPRSS3 in auditory neurons.

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.

Searching for the Molecular Basis of Partial Deafness

Hearing is an important human sense for communicating and connecting with others. Partial deafness (PD) is a common hearing problem, in which there is a down-sloping audiogram. In this study, we apply a practical system for classifying PD patients, used for treatment purposes, to distinguish two groups of patients: one with almost normal hearing thresholds at low frequencies (PDT-EC, n = 20), and a second group with poorer thresholds at those same low frequencies (PDT-EAS, n = 20). After performing comprehensive genetic testing with a panel of 237 genes, we found that genetic factors can explain a significant proportion of both PDT-EC and PDT-EAS hearing losses, accounting, respectively, for approx. one-fifth and one-half of all the cases in our cohort. Most of the causative variants were located in dominant and recessive genes previously linked to PD, but more than half of the variants were novel. Among the contributors to PDT-EC we identified OSBPL2 and SYNE4, two relatively new hereditary hearing loss genes with a low publication profile. Our study revealed that, for all PD patients, a postlingual hearing loss more severe in the low-frequency range is associated with a higher detection rate of causative variants. Isolating a genetic cause of PD is important in terms of prognosis, therapeutic effectiveness, and risk of recurrence.

TMPRSS3 Gene Variants With Implications for Auditory Treatment and Counseling

Objective: To identify and report novel variants in the TMPRSS3 gene and their clinical manifestations related to hearing loss as well as intervention outcomes. This information will be helpful for genetic counseling and treatment planning for these patients.

Methods: Literature review of previously reported TMPRSS3 variants was conducted. Reported variants and associated clinical information was compiled. Additionally, cohort data from 18 patients, and their families, with a positive result for TMPRSS3-associated hearing loss were analyzed. Genetic testing included sequencing and copy number variation (CNV) analysis of TMPRSS3 and the Laboratory for Molecular Medicine’s OtoGenome-v1, -v2, or -v3 panels. Clinical data regarding patient hearing rehabilitation was interpreted along with their genetic testing results and in the context of previously reported cochlear implant outcomes in individuals with TMPRSS3 variants.

Results: There have been 87 previously reported TMPRSS3 variants associated with non-syndromic hearing loss in more than 20 ancestral groups worldwide. Here we report occurrences of known variants as well as one novel variant: deletion of Exons 1–5 and 13 identified from our cohort of 18 patients. The hearing impairment in many of these families was consistent with that of previously reported patients with TMPRSS3 variants (i.e., typical down-sloping audiogram). Four patients from our cohort underwent cochlear implantation.

Conclusion: Bi-allelic variants of TMPRSS3 are associated with down-sloping hearing loss regardless of ancestry. The outcome following cochlear implantation in patients with variants of TMPRSS3 is excellent. Therefore, cochlear implantation is strongly recommended for hearing rehabilitation in these patients.

Milestones toward cochlear gene therapy for patients with hereditary hearing loss

A number of genes are reportedly responsible for hereditary hearing loss, which accounts for over 50% of all congenital hearing loss cases. Recent advances in genetic testing have enabled the identification of pathogenic variants in many cases, and systems have been developed to provide personalized treatment based on etiology. Gene therapy is expected to become an unprecedented curative treatment. Several reports have demonstrated the successful use of cochlear gene therapy to restore auditory function in mouse models of genetic deafness; however, many hurdles remain to its clinical application in humans. Herein, we focus on the frequency of deafness genes in patients with congenital and late-onset progressive hearing loss and discuss the following points regarding which genes need to be targeted to efficiently proceed with clinical application: (a) which cells' genes are expressed within the cochlea, (b) whether gene transfer to the targeted cells is possible using vectors such as adeno-associated virus, (c) what phenotype of hearing loss in patients is exhibited, and (d) whether mouse models exist to verify the effectiveness of treatment. Moreover, at the start of clinical application, gene therapy in combination with cochlear implantation may be useful for cases of progressive hearing loss.

The genetic etiology of hearing loss in Japan revealed by the social health insurance-based genetic testing of 10K patients

Etiological studies have shown genetic disorders to be a major cause of sensorineural hearing loss, but there are a limited number of comprehensive etiological reports based on genetic analysis. In the present study, the same platform using a diagnostic DNA panel carrying 63 deafness genes and the same filtering algorithm were applied to 10,047 samples obtained from social health insurance-based genetic testing of hearing loss. The most remarkable result obtained in this comprehensive study was that the data first clarified the genetic epidemiology from congenital/early-onset deafness to late-onset hearing loss. The overall diagnostic rate was 38.8%, with the rate differing for each age group; 48.6% for the congenital/early-onset group (~5y.o.), 33.5% for the juvenile/young adult-onset group, and 18.0% for the 40+ y.o. group. Interestingly, each group showed a different kind of causative gene. With regard to the mutational spectra, there are certain recurrent variants that may be due to founder effects or hot spots. A series of haplotype studies have shown many recurrent variants are due to founder effects, which is compatible with human migration. It should be noted that, regardless of differences in the mutational spectrum, the clinical characteristics caused by particular genes can be considered universal. This comprehensive review clarified the detailed clinical characteristics (onset age, severity, progressiveness, etc.) of hearing loss caused by each gene, and will provide useful information for future clinical application, including genetic counseling and selection of appropriate interventions.

Cochlear Implantation and Electric Acoustic Stimulation in Children With TMPRSS3 Genetic Mutation

BACKGROUND

Mutations in the TMPRSS3 gene, although rare, can cause high frequency hearing loss with residual hearing at low frequencies. Several previous studies have reported cochlear implant (CI) outcomes for adults with TMPRSS3 mutation with mixed results. Although some studies have suggested that TMPRSS3 is expressed in spiral ganglion cells, it remains unclear if previously reported poor CI outcomes in this population were secondary to long durations of deafness or to the effects of the TMPRSS3 mutation. To date, no studies in the literature have reported CI outcomes for children with TMPRSS3 mutation treated with CI.

OBJECTIVE

The current case series aimed to describe outcomes for three children with sloping hearing loss caused by TMPRSS3 mutation who underwent bilateral CI.

STUDY DESIGN

Case series.

SETTING

Academic medical center.

PATIENTS

Three children (3-4 yr) with TMPRSS3 mutation and normal sloping to profound high frequency hearing loss.

INTERVENTIONS

CI and electric acoustic stimulation (EAS).

MAIN OUTCOME MEASURES

Outcome measures were residual hearing thresholds, speech recognition scores, and electrode placement determined via intraoperative CT imaging.

RESULTS

All three children maintained residual acoustic hearing and received benefit from EAS. Mean change in low-frequency pure-tone average was 17 dB. Mean postoperative word and sentence recognition scores in the bilateral EAS condition were 80 and 75%, respectively.

CONCLUSIONS

Results indicate that CI with EAS is an appropriate treatment for children with TMPRSS3 genetic mutation. Pediatric results from this case series show more favorable CI outcomes than are currently reported for adults with TMPRSS3 mutation suggesting that the intervention may be time sensitive.

Screening Strategies for Deafness Genes and Functional Outcomes in Cochlear Implant Patients

OBJECTIVES

To review the current state of knowledge about the influence of specific genetic mutations that cause sensorineural hearing loss (SNHL) on cochlear implant (CI) functional outcomes, and how this knowledge may be integrated into clinical practice. A multistep and sequential population-based genetic algorithm suitable for the identification of congenital SNHL mutations before CI placement is also examined.

DATA SOURCES, STUDY SELECTION

A review was performed of the English literature from 2000 to 2019 using PubMed regarding the influence of specific mutations on CI outcomes and the use of next-generation sequencing for genetic screening of CI patients.

CONCLUSION

CI is an effective habilitation option for patients with severe-profound congenital SNHL. However, it is well known that CI outcomes show substantial inter-patient variation. Recent advances in genetic studies have improved our understanding of genotype-phenotype relationships for many of the mutations underlying congenital SNHL, and have explored how these relationships may account for some of the variance seen in CI performance outcomes. A sequential genetic screening strategy utilizing next-generation sequencing-based population-specific gene panels may allow for more efficient mutation identification before CI placement. Understanding the relationships between specific mutations and CI outcomes along with integrating routine comprehensive genetic testing into pre-CI evaluations will allow for more effective patient counseling and open the door for the development of mutation-specific treatment strategies.

Auditory Neuropathy Spectrum Disorders: From Diagnosis to Treatment: Literature Review and Case Reports

Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing impairments characterized by deteriorated speech perception, despite relatively preserved pure-tone detection thresholds. Affected individuals usually present with abnormal auditory brainstem responses (ABRs), but normal otoacoustic emissions (OAEs). These electrophysiological characteristics have led to the hypothesis that ANSD may be caused by various dysfunctions at the cochlear inner hair cell (IHC) and spiral ganglion neuron (SGN) levels, while the activity of outer hair cells (OHCs) is preserved, resulting in discrepancies between pure-tone and speech comprehension thresholds. The exact prevalence of ANSD remains unknown; clinical findings show a large variability among subjects with hearing impairment ranging from mild to profound hearing loss. A wide range of prenatal and postnatal etiologies have been proposed. The study of genetics and of the implicated sites of lesion correlated with clinical findings have also led to a better understanding of the molecular mechanisms underlying the various forms of ANSD, and may guide clinicians in better screening, assessment and treatment of ANSD patients. Besides OAEs and ABRs, audiological assessment includes stapedial reflex measurements, supraliminal psychoacoustic tests, electrocochleography (ECochG), auditory steady-state responses (ASSRs) and cortical auditory evoked potentials (CAEPs). Hearing aids are indicated in the treatment of ANSD with mild to moderate hearing loss, whereas cochlear implantation is the first choice of treatment in case of profound hearing loss, especially in case of IHC presynaptic disorders, or in case of poor auditory outcomes with conventional hearing aids.

The molecular etiology of deafness and auditory performance in the postlingually deafened cochlear implantees

Recent advances in molecular genetic testing (MGT) have improved identification of genetic aetiology of candidates for cochlear implantation (CI). However, whether genetic information increases CI outcome predictability in post-lingual deafness remains unclear. Therefore, we evaluated the outcomes of CI with respect to genetic aetiology and clinical predictors by comparing the data of study subjects; those with an identified genetic aetiology (GD group), and those without identifiable variants (GUD group). First, we identified the genetic aetiology in 21 of 40 subjects and also observed genetic etiologic heterogeneity. The GD group demonstrated significantly greater improvement in speech perception scores over a 1-year period than did the GUD group. Further, inverse correlation between deafness duration and the 1-year improvement in speech perception scores was tighter in the GD group than in the GUD group. The weak correlation between deafness duration and CI outcomes in the GUD group might suggest the pathophysiology underlying GUD already significantly involves the cortex, leading to lesser sensitivity to further cortex issues such as deafness duration. Under our MGT protocol, the correlation between deafness duration and CI outcomes were found to rely on the presence of identifiable genetic aetiology, strongly advocating early CI in individual with proven genetic aetiologies.

Cochlear Implantation From the Perspective of Genetic Background

While cochlear implantation (CI) technology has greatly improved over the past 40 years, one aspect of CI that continues to pose difficulties is the variability of outcomes due to numerous factors involved in postimplantation performance. The electric acoustic stimulation (EAS) system has expanded indications for CI to include patients with residual hearing, and is currently becoming a standard therapy for these patients. Genetic disorders are known to be the most common cause of congenital/early-onset sensorineural hearing loss, and are also involved in a considerable proportion of cases of late-onset hearing loss. There has been a great deal of progress in the identification of deafness genes over the last two decades. Currently, more than 100 genes have been reported to be associated with non-syndromic hearing loss. Patients possessing a variety of deafness gene mutations have achieved satisfactory auditory performance after CI/EAS, suggesting that identification of the genetic background facilitates prediction of post-CI/EAS performance. When the intra-cochlear etiology is associated with a specific genetic background, there is a potential for good CI performance. Thus, it is essential to determine which region of the cochlea is affected by identifying the responsible genes. This review summarizes the genetic background of the patients receiving CI/EAS, and introduces detailed clinical data and CI/EAS outcomes in representative examples. Anat Rec, 303:563-593, 2020. © 2020 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Auditory synaptopathy, auditory neuropathy, and cochlear implantation

Cochlear implantation has become the standard-of-care for adults and children with severe to profound hearing loss. There is growing evidence that qualitative as well as quantitative deficits in the auditory nerve may affect cochlear implant (CI) outcomes. Auditory neuropathy spectrum disorder (ANSD) is characterized by dysfunctional transmission of sound from the cochlea to the brain due to defective synaptic function or neural conduction. In this review, we examine the precise mechanisms of genetic lesions causing ANSD and the effect of these lesions on CI outcomes. Reviewed data show that individuals with lesions that primarily affect the cochlear sensory system and the synapse, which are bypassed by the CI, have optimal CI outcomes. Individuals with lesions that affect the auditory nerve show poor performance with CIs, likely because neural transmission of the electrical signal from the CI is affected. We put forth a nuanced molecular classification of ANSD that has implications for preoperative counseling for patients with this disorder prior to cochlear implantation. We propose that description of ANSD patients should be based on the molecular site of lesion typically derived from genetic evaluation (synaptopathy vs. neuropathy) as this has implications for expected CI outcomes. Improvements in our understanding of genetic site of lesions and their effects on CI function should lead to better CI outcomes, not just for individuals with auditory neuropathy, but all individuals with hearing loss.

In Vivo Electrocochleography in Hybrid Cochlear Implant Users Implicates TMPRSS3 in Spiral Ganglion Function

Cochlear implantation, a surgical method to bypass cochlear hair cells and directly stimulate the spiral ganglion, is the standard treatment for severe-to-profound hearing loss. Changes in cochlear implant electrode array design and surgical approach now allow for preservation of acoustic hearing in the implanted ear. Electrocochleography (ECochG) was performed in eight hearing preservation subjects to assess hair cell and neural function and elucidate underlying genetic hearing loss. Three subjects had pathogenic variants in TMPRSS3 and five had pathogenic variants in genes known to affect the cochlear sensory partition. The mechanism by which variants in TMPRSS3 cause genetic hearing loss is unknown. We used a 500-Hz tone burst to record ECochG responses from an intracochlear electrode. Responses consist of a cochlear microphonic (hair cell) and an auditory nerve neurophonic. Cochlear microphonics did not differ between groups. Auditory nerve neurophonics were smaller, on average, in subjects with TMPRSS3 deafness. Results of this proof-of-concept study provide evidence that pathogenic variants in TMPRSS3 may impact function of the spiral ganglion. While ECochG as a clinical and research tool has been around for decades, this study illustrates a new application of ECochG in the study of genetic hearing and deafness in vivo.

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.

The Analysis of A Frequent TMPRSS3 Allele Containing P.V116M and P.V291L in A Cis Configuration among Deaf Koreans

We performed targeted re-sequencing to identify the genetic etiology of early-onset postlingual deafness and encountered a frequent TMPRSS3 allele harboring two variants in a cis configuration. We aimed to evaluate the pathogenicity of the allele. Among 88 cochlear implantees with autosomal recessive non-syndromic hearing loss, subjects with GJB2 and SLC26A4 mutations were excluded. Thirty-one probands manifesting early-onset postlingual deafness were sorted. Through targeted re-sequencing, we detected two families with a TMPRSS3 mutant allele containing p.V116M and p.V291L in a cis configuration, p.[p.V116M; p.V291L]. A minor allele frequency was calculated and proteolytic activity was measured. A p.[p.V116M; p.V291L] allele demonstrated a significantly higher frequency compared to normal controls and merited attention due to its high frequency (4.84%, 3/62). The first family showed a novel deleterious splice site variant—c.783-1G>A—in a trans allele, while the other showed homozygosity. The progression to deafness was noted within the first decade, suggesting DFNB10. The proteolytic activity was significantly reduced, confirming the severe pathogenicity. This frequent mutant allele significantly contributes to early-onset postlingual deafness in Koreans. For clinical implication and proper auditory rehabilitation, it is important to pay attention to this allele with a severe pathogenic potential.

Identification of a rare COCH mutation by whole-exome sequencing : Implications for personalized therapeutic rehabilitation in an Austrian family with non-syndromic autosomal dominant late-onset hearing loss

Background

Non-syndromic autosomal dominant hearing impairment is characteristically postlingual in onset. Genetic diagnostics are essential for genetic counselling, disease prognosis and understanding of the molecular mechanisms of disease. To date, 36 causative genes have been identified, many in only individual families. Gene selection for genetic screening by traditional methods and genetic diagnosis in autosomal dominant patients has therefore been fraught with difficulty. Whole-exome sequencing provides a powerful tool to analyze all protein-coding genomic regions in parallel, thus allowing the comprehensive screening of all known genes and associated alterations.

Methods

In this study, a previously undiagnosed late-onset progressive autosomal dominant hearing loss in an Austrian family was investigated by means of whole-exome sequencing. Results were confirmed by Sanger sequencing.

Results

A previously described c.151C>T missense (p.Pro51Ser) mutation in the LCCL (limulus factor C, cochlin, late gestation lung protein Lgl1) domain of the cochlin gene (COCH) was identified as causative and segregated with disease in five members of the family. Molecular diagnostics led to the decision to perform cochlear implantation in an index patient who subsequently showed excellent postoperative auditory performance. The c.151C>T mutation was not found in 18 screened Austrian families with autosomal dominant hearing loss but was represented alongside other known pathogenic mutant COCH alleles in the Genome Aggregation Database (gnomAD) in European populations. A combined allele frequency of 0.000128 implies an orphan disease frequency for COCH-induced hearing loss of 1:3900 in Europe.

Conclusions

Exome sequencing successfully resolved the genetic diagnosis in a family suffering from autosomal dominant hearing impairment and allowed prediction of purported auditory outcome after cochlear implantation in an index patient. Personalized treatment approaches based on the molecular mechanisms of disease may become increasingly important in the future.

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.

Laser-capture micro dissection combined with next-generation sequencing analysis of cell type-specific deafness gene expression in the mouse cochlea

Cochlear implantation (CI), which directly stimulates the cochlear nerves, is the most effective and widely used medical intervention for patients with severe to profound sensorineural hearing loss. The etiology of the hearing loss is speculated to have a major influence of CI outcomes, particularly in cases resulting from mutations in genes preferentially expressed in the spiral ganglion region. To elucidate precise gene expression levels in each part of the cochlea, we performed laser-capture micro dissection in combination with next-generation sequencing analysis and determined the expression levels of all known deafness-associated genes in the organ of Corti, spiral ganglion, lateral wall, and spiral limbs. The results were generally consistent with previous reports based on immunocytochemistry or in situ hybridization. As a notable result, the genes associated with many kinds of syndromic hearing loss (such as Clpp, Hars2, Hsd17b4, Lars2 for Perrault syndrome, Polr1c and Polr1d for Treacher Collins syndrome, Ndp for Norrie Disease, Kal for Kallmann syndrome, Edn3 and Snai2 for Waardenburg Syndrome, Col4a3 for Alport syndrome, Sema3e for CHARGE syndrome, Col9a1 for Sticker syndrome, Cdh23, Cib2, Clrn1, Pcdh15, Ush1c, Ush2a, Whrn for Usher syndrome and Wfs1 for Wolfram syndrome) showed higher levels of expression in the spiral ganglion than in other parts of the cochlea. This dataset will provide a base for more detailed analysis in order to clarify gene functions in the cochlea as well as predict CI outcomes based on gene expression data.

Navigating genetic diagnostics in patients with hearing loss

PURPOSE OF REVIEW

In the age of targeted genomic enrichment and massively parallel sequencing, there is no more efficient genetic testing method for the diagnosis of hereditary hearing loss. More clinical tests are on the market, which can make choosing good tests difficult.

RECENT FINDINGS

More and larger comprehensive genetic studies in patients with hearing loss have been published recently. They remind us of the importance of looking for both single nucleotide variation and copy number variation in all genes implicated in nonsyndromic hearing loss. They also inform us of how a patient's history and phenotype provide essential information in the interpretation of genetic data.

SUMMARY

Choosing the most comprehensive genetic test improves the chances of a genetic diagnosis and thereby impacts clinical care.

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.