Vestibular Deficits in Deafness: Clinical Presentation, Animal Modeling, and Treatment Solutions

Advancing precision ear medicine: leveraging animal models for disease insights and therapeutic innovations

Gene therapy offers significant promise for treating inner ear disorders, but its clinical translation requires robust preclinical validation, often reliant on animal models. This review examines the role of these models in advancing gene therapeutics for inherited inner ear disorders, focusing on successes, challenges, and treatment solutions. By providing a precise understanding of disease mechanisms, these models offer a versatile preclinical platform that is essential for assessing and validating therapies. Successful gene supplementation and editing have shown potential in restoring hearing and balance functions and preventing their decline. However, challenges such as limitations in gene delivery methods, surgical access, immune responses, and discrepancies in disease manifestation between animal models and humans hinder clinical translation. Current efforts are dedicated to developing innovative strategies aimed at enhancing the efficiency of gene delivery, overcoming physical barriers such as the blood-labyrinth barrier, improving target specificity, and maximizing therapeutic efficacy while minimizing adverse immune responses. Diverse gene supplementation and editing strategies, along with evolving technologies, hold promise for maximizing therapeutic outcomes using disease relevant models. The future of inner ear gene therapeutics will hinge on personalized therapies and team science fueling interdisciplinary collaborations among researchers, clinicians, companies, and regulatory agencies to expedite the translation from bench to bedside and unlock the immense potential of precision medicine in the inner ear.

Cell tropism of adeno-associated viruses within the mouse inner ear in vivo: from embryonic to adult stages

Adeno-associated virus (AAV)-based gene therapy is emerging as a promising treatment for deafness and vestibular deficits, due to the variety of available serotypes that offer a large range of cell targeting capabilities. Nevertheless, the tropism of these AAV serotypes for sensory inner ear cells varies greatly as the cochlea matures, presenting a significant burden for successful preclinical trials. Therefore, identifying serotypes with strong tropism for cochlear and vestibular hair cells during key stages of development in mouse inner ear, the most widely used preclinical model, is essential for advancing clinical applications. We conducted a comparative analysis of the cellular tropism and hair-cell transduction rates of four AAV serotypes in the cochlea and vestibular organs during maturation. We used AAV2, AAV8, AAV9-PHP.eB, and Anc80L65 at the embryonic, neonatal, and adult stages. Our results indicate that the cell transduction rate of these four serotypes varies with age. Notably outer hair cells were mostly targeted during the embryonic stage, inner hair cells were primarily transduced principally at the mature stage, and vestibular hair cells were the most permissive at the neonatal stage. These results provide new insights for preclinical gene therapy studies for the inner ear with potential implications for therapeutic outcomes.

Association of Tinnitus with Benign Paroxysmal Positional Vertigo

Background/Objectives: The purpose of this study is to investigate the potential association between tinnitus and benign paroxysmal positional vertigo (BPPV) using large-scale population data to assess the risk of developing one condition in patients who have the other condition. Methods: Using claims data from the National Health Insurance Corporation spanning 2008 to 2021, we conducted a comprehensive analysis to estimate the risk of developing BPPV in patients with tinnitus and vice versa. This study involved 580,531 patients with tinnitus, 572,937 patients with benign paroxysmal positional vertigo, and their corresponding controls. We used propensity score matching and statistical analyses, including Cox proportional hazard models to assess the association between these conditions. Results: The incidence of BPPV in patients with tinnitus was significantly higher (12.3 per 1000 individuals per year) than that of controls (5.1 per 1000 individuals per year), with an adjusted hazard ratio of 2.474. Additionally, the incidence of tinnitus was significantly higher in patients with BPPV (11.7 per 1000 individuals per year) than in controls (5.5 per 1000 individuals per year), with an adjusted hazard ratio of 2.048. Subgroup analysis showed the risk of developing BPPV in people with tinnitus, and vice versa, was higher in young vs. old people (<39 years) and in men vs. women (p<0.0001). These findings remained significant even after adjusting for sex, age, medical benefits, disability, and health habits. Conclusions: This study provides substantial evidence for a bidirectional association between tinnitus and benign paroxysmal positional vertigo, suggesting an interconnected pathophysiology. Further research is warranted to understand the underlying mechanisms.

Vestibular Assessment in Infants with Congenital or Early Onset Sensorineural Hearing Loss: Is Neonatal Vestibular Screening Required? A Scoping Review

BACKGROUND/OBJECTIVES

Children with congenital or early onset sensorineural hearing loss (SNHL) are at a greater risk of vestibular dysfunction (VD), hypothesized to occur from the close embryological relationship between the cochlear and vestibular systems. Even with increasing focus on early detection and rehabilitation through Universal Newborn Hearing Screening (UNHS) programmes in many countries, few studies have focused on the prevalence and feasibility of vestibular assessment in infant populations. The objectives of this review are to 1. identify the prevalence of VD infants with congenital or early onset (<12 months old) SNHL, 2. identify which vestibular assessment tests/protocols are conducted on this population, 3. report sensitivity and specificity values for identified vestibular assessment tests/protocols.

METHODS

Studies that included infants aged 0-12 months, with congenital or early onset SNHL of any laterality, degree, or configuration, and who underwent any method of vestibular assessment were included. The review adhered to the Joanna Briggs Institute (JBI) guidance and the PRISMA-ScR extension statement.

RESULTS

A total of 18 studies were included in the review. All articles reported that infants with congenital or early onset SNHL are at a greater risk of VD, particularly those with bilateral severe-profound SNHL. The cervical vestibular-evoked myogenic potentials (cVEMP) test was the most frequently identified vestibular assessment tool for this age demographic.

CONCLUSIONS

Results from the included articles coincide with results from literature assessing older paediatric populations. cVEMPs have been reported to be a feasible, sensitive, and specific screening tool in infants with congenital or early onset SNHL. The prevalence of VD in infants with congenital or early onset SNHL justify further investigation on the feasibility of establishing a pathway for vestibular assessment for all infants referred by UNHS programmes.

Serum Otoconin-90 and Otolin-1 Concentrations in Benign Paroxysmal Positional Vertigo

OBJECTIVE

The aim was to evaluate the value of otolith-associated protein otoconin-90 (OC90) and otolin-1 in the pathogenesis research and clinical treatment of benign paroxysmal positional vertigo (BPPV).

MATERIAL AND METHOD

The study included 50 patients with BPPV admitted to neurology and otorhinolaryngology departments and 30 healthy subjects with no history of dizziness as a control group.

RESULTS

BPPV and controls were similar in terms of gender and age. Otolin-1 concentration was significantly greater in the BPPV group than in the controls (710.44 [584.35-837.39] vs 280.45 [212.7-419.61]; p < 0.001). No statistical significance was found, although OC90 was higher in the BPPV group than in the controls. There was a strong positive correlation between otolin-1 and OC90, a moderate negative correlation between otolin-1 and vitamin D, and a strong negative correlation between OC90 and vitamin D in the BPPV patient group. Otolin-1 had high specificity and AUC values for BPPV (AUC: 0.933; 95% CI: 0.881-0.986, 79.2% sensitivity, 100% specificity with a cutoff greater than 525).

CONCLUSIONS

High serum concentrations of otolin-1 were associated with an increased risk of BPPV, but high concentrations of OC90 were not. Serum concentrations of otolin-1 can potentially be used as a biomarker for the acute onset of inner ear disorders due to the significant increase in patients with BPPV. Vitamin D has high specificity and sensitivity in patients with BPPV. It also provides evidence that BPPV patients with vitamin D deficiency may improve their symptoms with replacement therapy. More large-scale prospective studies are required to confirm these associations and clarify the exact mechanisms.

Prevalence and risk factors of self-reported hearing loss, tinnitus, and dizziness in a population-based sample from rural northeastern Germany

A close anatomical and physiological relationship is known between the senses of hearing and balance, while an additional pathophysiological interaction is supposed. The mechanisms underlying this association are not yet fully understood, especially in individuals without a known specific otologic disorder. In particular, only scarce information on the combined occurrence of audiovestibular sensory impairment is available so far. Therefore, this study aims to provide further insight into the prevalence and co-prevalence of the audiovestibular symptoms hearing loss, tinnitus and dizziness. Additionally, the influence of potential risk factors from lifestyle habits as well as cardiovascular and metabolic conditions on the development of those symptoms is studied. Data was analyzed from 8134 individuals from the population-based Study of Health in Pomerania (SHIP). SHIP pursues a broad and comprehensive examination program in chronologically separated cohorts with longitudinal follow-up. Cohorts are sampled from Western Pomerania, a rural region of north-eastern Germany. The study population represents a cross-sectional analysis from the cohorts SHIP-START (recruited 1997-2001) and SHIP-TREND (recruited 2008-2012), sampled for baseline investigations (SHIP-START-0 and SHIP-TREND-0) at the age of 20-79 years. Audiovestibular symptoms as outcome variables were assessed by structured questionnaires. Additionally, individuals were comprehensively characterized regarding modifiable lifestyle factors as well as cardiovascular and metabolic disorders, allowing the assessment of their role as exposure variables. We calculated a weighted prevalence of 14.2% for hearing loss, 9.7% for tinnitus, and 13.5% for dizziness in the population. Prevalence increased with age and differed among the sexes. A considerable share of 28.0% of the investigated individuals reported more than one symptom at once. The prevalence of hearing loss as well as tinnitus increased between the two cohorts. A moderate positive correlation was found between the occurrence of hearing loss and tinnitus (phi-coefficient 0.318). In multivariable regression analyses, education was identified as a significant protective factor while only smoking was significantly associated with all three symptoms. Furthermore, several cardiovascular risk factors contributed to both hearing loss and dizziness. In conclusion, audiovestibular symptoms are highly prevalent in the investigated population. A considerable but complex influence of risk factors points towards a relation with neuronal as well as cardiovascular disease processes. To clarify the underlying mechanisms, the interaction between the senses of hearing and balance as well as the mode of action of the risk factors should be evaluated in more detail in the future.

Evaluating the impact of COVID-19 on vertigo and hearing impairment: A post-recovery analysis

The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, has manifested with respiratory symptoms and a spectrum of extra-pulmonary complications. Emerging evidence suggests potential impacts on the auditory and vestibular systems, but the extent and nature of these effects in recovered individuals remain unclear. This study aimed to investigate the prevalence and severity of vertigo and hearing impairment in individuals who have recovered from COVID-19 and to identify potential risk factors associated with these sensory symptoms. A cohort of 250 recovered COVID-19 patients was assessed. Standardized questionnaires, including the Dizziness Handicap Inventory and the Vertigo Symptom Scale, were used to evaluate vertigo. Hearing assessment was conducted using pure-tone audiometry, speech audiometry, tympanometry, and oto-acoustic emissions testing. Logistic regression analysis was performed to assess the association between COVID-19 severity and the occurrence of sensory symptoms, controlling for confounding variables such as age and comorbidities. Of the participants, 10% reported vertigo, varying severity. Hearing assessments revealed that most participants had normal hearing, with an average speech discrimination score of 94.6. Logistic regression analysis indicated a significant association between severe COVID-19 and an increased likelihood of vertigo (OR 2.11, 95% CI 1.02-4.35, P = .043) and hearing impairment (OR 3.29, 95% CI 1.60-6.78, P = .002). This study suggests a significant association between COVID-19 severity and vertigo and hearing impairment prevalence. The findings underscore the importance of sensory symptom assessment in the post-recovery phase of COVID-19, highlighting the need for comprehensive healthcare approaches to manage long-term sequelae.

Single-cell transcriptomic atlas reveals increased regeneration in diseased human inner ear balance organs

Mammalian inner ear hair cell loss leads to permanent hearing and balance dysfunction. In contrast to the cochlea, vestibular hair cells of the murine utricle have some regenerative capacity. Whether human utricular hair cells regenerate in vivo remains unknown. Here we procured live, mature utricles from organ donors and vestibular schwannoma patients, and present a validated single-cell transcriptomic atlas at unprecedented resolution. We describe markers of 13 sensory and non-sensory cell types, with partial overlap and correlation between transcriptomes of human and mouse hair cells and supporting cells. We further uncover transcriptomes unique to hair cell precursors, which are unexpectedly 14-fold more abundant in vestibular schwannoma utricles, demonstrating the existence of ongoing regeneration in humans. Lastly, supporting cell-to-hair cell trajectory analysis revealed 5 distinct patterns of dynamic gene expression and associated pathways, including Wnt and IGF-1 signaling. Our dataset constitutes a foundational resource, accessible via a web-based interface, serving to advance knowledge of the normal and diseased human inner ear.

Clarin-2 gene supplementation durably preserves hearing in a model of progressive hearing loss

Hearing loss is a major health concern affecting millions of people worldwide with currently limited treatment options. In clarin-2-deficient Clrn2-/- mice, used here as a model of progressive hearing loss, we report synaptic auditory abnormalities in addition to the previously demonstrated defects of hair bundle structure and mechanoelectrical transduction. We sought an in-depth evaluation of viral-mediated gene delivery as a therapy for these hearing-impaired mice. Supplementation with either the murine Clrn2 or human CLRN2 genes preserved normal hearing in treated Clrn2-/- mice. Conversely, mutated forms of CLRN2, identified in patients with post-lingual moderate to severe hearing loss, failed to prevent hearing loss. The ectopic expression of clarin-2 successfully prevented the loss of stereocilia, maintained normal mechanoelectrical transduction, preserved inner hair cell synaptic function, and ensured near-normal hearing thresholds over time. Maximal hearing preservation was observed when Clrn2 was delivered prior to the loss of transducing stereocilia. Our findings demonstrate that gene therapy is effective for the treatment of post-lingual hearing impairment and age-related deafness associated with CLRN2 patient mutations.

RIPOR2: A new gene of non-syndromic cochleovestibular dysfunction, discrepancy between human pathology and animal models

Cochleovestibular dysfunctions are rare conditions misrecognized. A homozygous pathogenic variation c.1561C > T (p.Arg521*) in RIPOR2 (RHO family interacting cell polarization regulator 2) has been identified by WES in Tunisian siblings suffering from congenital bilateral profound hearing and vestibular dysfunctions. In contrast to the vestibular areflexia observed in our patients, deaf Ripor2 KO mouse model and our zebrafish model have normal vestibular function.

mTORC2 regulates auditory hair cell structure and function

mTOR broadly controls cell growth, but little is known about the role of mTOR complex 2 (mTORC2) in the inner ear. To investigate the role of mTORC2 in sensory hair cells (HCs), we generated HC-specific Rictor knockout (HC-RicKO) mice. HC-RicKO mice exhibited early-onset, progressive, and profound hearing loss. Increased DPOAE thresholds indicated outer HC dysfunction. HCs are lost, but this occurs after hearing loss. Ultrastructural analysis revealed stunted and absent stereocilia in outer HCs. In inner HCs, the number of synapses was significantly decreased and the remaining synapses displayed a disrupted actin cytoskeleton and disorganized Ca2+ channels. Thus, the mTORC2 signaling pathway plays an important role in regulating auditory HC structure and function via regulation of the actin cytoskeleton. These results provide molecular insights on a central regulator of cochlear HCs and thus hearing.

Normative values for the video Head Impulse Test in children without otoneurologic symptoms and their evolution across childhood by gender

PURPOSE

The video Head Impulse Test is routinely used to assess semicircular canal function in adults, but to date, pediatric reference values are scarce. This study aimed to explore the vestibulo-ocular reflex (VOR) in healthy children at different development stages and to compare the obtained gain values with reference to those in an adult population.

METHODS

This prospective, single-center study recruited 187 children from among patients without otoneurological diseases, healthy relatives of these patients, and staff families from a tertiary hospital. Patients were divided into three groups by age: 3-6 years, 7-10 years, and 11-16 years. The vestibulo-ocular reflex was assessed by video Head Impulse Test, using a device with a high-speed infrared camera and accelerometer (EyeSeeCam®; Interacoustics, Denmark).

RESULTS

We found a lower vestibulo-ocular reflex gain of both horizontal canals in the 3-6-year-old group when compared with the other age groups. No increasing trend was found in the horizontal canals from age 7-10 years to age 11-16 years, and no differences were found by sex.

CONCLUSION

Gain values in the horizontal canals increased with age until children reached age 7-10 years and matched the normal values for adults.

Paediatric vestibular assessment in French cochlear implant centres: Challenges and improvement areas

OBJECTIVE

Survey of paediatric vestibular activity in all 30 French paediatric cochlear implant (CI) centres to identify challenges and areas of improvement.

METHOD

All 30 French CI centres answered a 29-question questionnaire about their paediatric vestibular activity, equipment, and management in different clinical situations (e.g. vestibular assessment before a cochlear implantation or in cases of vertigo) at different ages.

RESULTS

Eighteen CI centres had dedicated paediatric vestibular clinics and 12 did not. Minimum age required for vestibular testing was 3 years in eight centres. Four vestibular tests stood out: caloric tests, video Head Impulse Test (vHIT), rotating chair, vestibular evoked myogenic potentials (VEMP). Depending on the centre's experience, the use of vestibular tests in clinical routine was very heterogeneous. Expert centres mostly used vHIT and cervical VEMP (in bone conduction) for assessments before the first cochlear implantation in 1-year-old children. Dizziness assessment in 4-year children was based on the use of vHIT, cervical VEMP on bone conduction, rotatory test, and caloric test. Ocular VEMP was rarely used.

CONCLUSIONS

Paediatric vestibular assessment requires specific expertise compared to adults. Due to a lack of specialised human resources, some centres may be unable to follow French paediatric CI guidelines. International recommendations could help standardise paediatric vestibular management and public health policies should be discussed to improve training and access for children.

Hearing Status and Static Postural Control of Collegiate Athletes

CONTEXT

Because of the close proximity of the cochlea, vestibular apparatus, and shared neurovascular structures, the static postural control of athletes who are deaf or hard of hearing (D/HoH) may be different from that of athletes who are hearing. Limited research is available to quantify differences between these athletes.

OBJECTIVE

To determine the effect of hearing status and stance condition on the static postural control of athletes.

DESIGN

Cross-sectional study.

SETTING

Athletic training facilities.

PATIENTS OR OTHER PARTICIPANTS

Fifty-five collegiate varsity athletes who were D/HoH (age = 20.62 ± 1.80 years, height = 1.73 ± 0.08 m, mass = 80.34 ± 18.92 kg) and 100 university club athletes who were hearing (age = 20.11 ± 1.59 years, height = 1.76 ± 0.09 m, mass = 77.66 ± 14.37 kg).

MAIN OUTCOME MEASURE(S)

Participants completed the Modified Clinical Test of Sensory Interaction and Balance on a triaxial force plate. Anteroposterior and mediolateral (ML) center-of-pressure (CoP) velocity, anteroposterior and ML CoP amplitude root mean square, and 95% ellipse sway area were calculated.

RESULTS

Athletes who were D/HoH had a larger CoP velocity, larger ML root mean square, and larger sway area than those who were hearing (P values < .01). A significant main effect of stance condition was observed for all postural control variables (P values < .01).

CONCLUSIONS

During the Modified Clinical Test of Sensory Interaction and Balance, athletes who were D/HoH demonstrated a larger sway area compared with athletes who were hearing. Therefore, individualized baseline assessments of static postural control may be warranted for athletes who are D/HoH as opposed to comparisons with existing normative data.