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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

LAY SUMMARY

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

Cochlear Implant Outcomes in Patients With TMTC2 -Associated Sensorineural Hearing Loss and Auditory Neuropathy/Auditory Dys-Synchrony

OBJECTIVE

To investigate the outcomes of cochlear implantation in patients with TMTC2 -associated sensorineural hearing loss and auditory neuropathy/auditory dys-synchrony.

PATIENTS

Adult and pediatric cochlear implant (CI) patients followed in an academic center who tested positive for TMTC2 genetic variant rs35725509.

INTERVENTION

Cochlear implantation.

MAIN OUTCOME MEASURES

Speech perception scores in quiet.

RESULTS

Ten CI patients were identified with TMTC2 variant rs35725509 out of 157 patients who underwent genetic testing (i.e., 6.3% of patients tested). All demonstrated progressive, bilateral hearing loss with severe-to-profound audiometric thresholds preoperatively. Pre-CI and 1-year post-CI speech recognition percent correct scores were compared. Post-CI speech perception (mean 61.0%, standard deviation 31.4%) was significantly higher than pre-CI speech perception (mean 21.0%, standard deviation 27.0%) ( p = 0.002). Individually, 9 of the 10 subjects experienced significant improvements in speech perception pre- to post-CI ( p < 0.05). Electrically evoked compound action potential measures were available for five patients, and all showed normal electrically evoked compound action potential thresholds.

CONCLUSION

Patients with TMTC2 -associated sensorineural hearing loss and auditory neuropathy/auditory dys-synchrony have significantly improved speech perception outcomes with cochlear implantation and should be considered candidates for this intervention if there are no other contraindications.

Vestibular Impairment and Postural Development in Children With Bilateral Profound Hearing Loss

Importance

Children with profound hearing loss (HL) and vestibular impairment have worse cochlear implant outcomes compared with those without vestibular impairment. However, the decision for cochlear implantation is rarely based on vestibular function assessment as a complement to audiologic testing.

Objectives

To identify the prevalence of vestibular impairment according to HL origin and to assess the association between vestibular impairment and delayed posturomotor development in children with profound HL.

Design, Setting, and Participants

This cohort study was conducted in a pediatric referral center for cochlear implantation in Paris, France, using medical records data on HL origin, vestibular assessment, and ages of developmental milestone achievement. The cohort included children with profound HL (loss >90 dB HL) who completed vestibular assessment prior to cochlear implantation between January 1, 2009, and December 31, 2019. Data analyses were conducted between January and June 2023.

Main Outcomes and Measures

The primary outcome was prevalence of vestibular impairment according to HL origin. Children were classified into 3 groups according to their responses to vestibular testing: normal vestibular function (NVF), partially impaired vestibular function (PVF), and complete bilateral vestibular loss (CBVL). Generalized logit models were performed to evaluate the association between vestibular impairment and causes of HL as well as posturomotor development delay.

Results

A total of 592 children were included (308 males [52.0%]; mean [SD] age, 38 [34] months). In children with documented HL origin (n = 266), 45.1% (120) had HL with genetic origin, 50.0% of which were syndromic (mainly Usher and Waardenburg syndromes) and 50.0% were nonsyndromic (mainly associated with connexin 26). Among patients with infectious HL origin (n = 74), 70.3% (52) had cytomegalovirus (CMV) infection. Vestibular impairment was found in 44.4% (263 of 592) of the children; it was mostly symmetrical in 88.9% (526) and was CBVL in 5.7% (34) of the cases. Vestibular impairment was present in 78.3% (47) of children with genetic syndromic HL (56.7% [34] with PVF; 21.7% [13] with CBVL) and in 69.2% (36) of children with CMV infection (57.7% [30] with PVF; 11.5% [6] with CBVL). Genetic syndromic HL origin was found to be more often associated with both PVF and CBVL than other HL causes. The odds of having delays in 4 developmental milestones (head holding, sitting, standing with support, and independent walking) were higher in both PVF and CBVL (eg, head-holding odds ratios: 2.55 and 4.79) compared with NVF, and the age of achieving these milestones was higher in CBVL than PVF (eg, head holding: 7.33 vs 4.03 years; P < .001). All 4 developmental milestones were associated with the degree of vestibular impairment.

Conclusions and Relevance

This cohort study found that among children with profound HL, vestibular impairment was prevalent, varied according to HL origin, and associated with posturomotor development; while all developmental milestones were associated with vestibular impairment severity, not all HL causes were associated with vestibular impairment severity. Children with profound HL may benefit from complete vestibular assessment before cochlear implantation, which would support early and adapted management, such as physical therapy for CBVL and cochlear implantation strategy.

Navigating the Usher Syndrome Genetic Landscape: An Evaluation of the Associations between Specific Genes and Quality Categories of Cochlear Implant Outcomes

Usher syndrome (US) is a clinically and genetically heterogeneous disorder that involves three main features: sensorineural hearing loss, retinitis pigmentosa (RP), and vestibular impairment. With a prevalence of 4-17/100,000, it is the most common cause of deaf-blindness worldwide. Genetic research has provided crucial insights into the complexity of US. Among nine confirmed causative genes, MYO7A and USH2A are major players in US types 1 and 2, respectively, whereas CRLN1 is the sole confirmed gene associated with type 3. Variants in these genes also contribute to isolated forms of hearing loss and RP, indicating intersecting molecular pathways. While hearing loss can be adequately managed with hearing aids or cochlear implants (CIs), approved RP treatment modalities are lacking. Gene replacement and editing, antisense oligonucleotides, and small-molecule drugs hold promise for halting RP progression and restoring vision, enhancing patients' quality of life. Massively parallel sequencing has identified gene variants (e.g., in PCDH15) that influence CI results. Accordingly, preoperative genetic examination appears valuable for predicting CI success. To explore genetic mutations in CI recipients and establish correlations between implant outcomes and involved genes, we comprehensively reviewed the literature to gather data covering a broad spectrum of CI outcomes across all known US-causative genes. Implant outcomes were categorized as excellent or very good, good, poor or fair, and very poor. Our review of 95 cochlear-implant patients with US, along with their CI outcomes, revealed the importance of presurgical genetic testing to elucidate potential challenges and provide tailored counseling to improve auditory outcomes. The multifaceted nature of US demands a comprehensive understanding and innovative interventions. Genetic insights drive therapeutic advancements, offering potential remedies for the retinal component of US. The synergy between genetics and therapeutics holds promise for individuals with US and may enhance their sensory experiences through customized interventions.

Usher syndrome: Genetic diagnosis and current therapeutic approaches

Usher Syndrome (USH) is the most common deaf-blind syndrome, affecting approximately 1 in 6000 people in the deaf population. This genetic condition is characterized by a combination of hearing loss (HL), retinitis pigmentosa, and, in some cases, vestibular areflexia. Among the subtypes of USH, USH type 1 is considered the most severe form, presenting profound bilateral congenital deafness, vestibular areflexia, and early onset RP. USH type 2 is the most common form, exhibiting congenital moderate to severe HL for low frequencies and severe to profound HL for high frequencies. Conversely, type 3 is the rarest, initially manifesting mild symptoms during childhood that become more prominent in the first decades of life. The dual impact of USH on both visual and auditory senses significantly impairs patients’ quality of life, restricting their daily activities and interactions with society. To date, 9 genes have been confirmed so far for USH: MYO7A, USH1C, CDH23, PCDH15, USH1G, USH2A, ADGRV1, WHRN and CLRN1. These genes are inherited in an autosomal recessive manner and encode proteins expressed in the inner ear and retina, leading to functional loss. Although non-genetic methods can assist in patient triage and disease extension evaluation, genetic and molecular tests play a pivotal role in providing genetic counseling, enabling appropriate gene therapy, and facilitating timely cochlear implantation (CI). The CRISPR/Cas9 system and viral-based gene replacement therapy have recently emerged as highly promising techniques for treating USH. Regarding drug therapy, PTC-124 and Nb54 have been identified as promising drug interventions for genetic HL in USH. Simultaneously, CI has proven to be critical in the restoration of hearing. This review aims to summarize the genetic and molecular diagnosis of USH and highlight the importance of early diagnosis in guiding appropriate treatment strategies and improving patient prognosis.

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."

Usher Syndrome

Usher syndrome (USH) is the most common genetic condition responsible for combined loss of hearing and vision. Balance disorders and bilateral vestibular areflexia are also observed in some cases. The syndrome was first described by Albrecht von Graefe in 1858, but later named by Charles Usher, who presented a large number of cases with hearing loss and retinopathy in 1914. USH has been grouped into three main clinical types: 1, 2, and 3, which are caused by mutations in different genes and are further divided into different subtypes. To date, nine causative genes have been identified and confirmed as responsible for the syndrome when mutated: MYO7A, USH1C, CDH23, PCDH15, and USH1G (SANS) for Usher type 1; USH2A, ADGRV1, and WHRN for Usher type 2; CLRN1 for Usher type 3. USH is inherited in an autosomal recessive pattern. Digenic, bi-allelic, and polygenic forms have also been reported, in addition to dominant or nonsyndromic forms of genetic mutations. This narrative review reports the causative forms, diagnosis, prognosis, epidemiology, rehabilitation, research, and new treatments of USH.

Usher Syndrome in the Inner Ear: Etiologies and Advances in Gene Therapy

Hearing loss is the most common sensory disorder with ~466 million people worldwide affected, representing about 5% of the population. A substantial portion of hearing loss is genetic. Hearing loss can either be non-syndromic, if hearing loss is the only clinical manifestation, or syndromic, if the hearing loss is accompanied by a collage of other clinical manifestations. Usher syndrome is a syndromic form of genetic hearing loss that is accompanied by impaired vision associated with retinitis pigmentosa and, in many cases, vestibular dysfunction. It is the most common cause of deaf-blindness. Currently cochlear implantation or hearing aids are the only treatments for Usher-related hearing loss. However, gene therapy has shown promise in treating Usher-related retinitis pigmentosa. Here we review how the etiologies of Usher-related hearing loss make it a good candidate for gene therapy and discuss how various forms of gene therapy could be applied to Usher-related hearing loss.