Increased Hearing Thresholds Research Articles

Hearing and Kidney: Effects of Chronic Kidney Disease on Various Auditory Parameters – Results from a Tertiary Care Hospital in India

Background: An association between chronic kidney disease (CKD) and hearing loss was first described in patients with Alport syndrome. Patients with CKD develop sensorineural hearing loss with the progression of the disease. Studies using BAER as an index of auditory function among patients with CKD showed evidence of various degrees of auditory dysfunction.
 Materials and methods: 100 adult CKD patients (stage 3 – 5 and 5D) and 50 controls were included in the study. Clinical and biochemical parameters were assessed and all the patients and controls underwent Pure Tone Audiometry (PTA) and Brainstem Auditory Evoked Response (BAER) evaluation.
 Results: When hearing thresholds were compared between the patients and controls PTA showed an increase in hearing threshold in all patient groups. This increase was more noticeable at higher frequencies (4 and 8 kHz). Compared with healthy controls, a highly significant delay was observed in CKD patients in both absolute and interpeak latencies in BAER in the present study.
 Conclusion: The present study provides a concrete evidence to the otherwise disputed relation of auditory function in CKD proving that hearing is permanently affected by ESRD at all levels of the auditory neural pathway.
 J MEDICINE JAN 2020; 21 (1) : 31-35

Tinnitus Correlates with Downregulation of Cortical Glutamate Decarboxylase 65 Expression But Not Auditory Cortical Map Reorganization.

Hearing loss is the biggest risk factor for tinnitus, and hearing-loss-related pathological changes in the auditory pathway have been hypothesized as the mechanism underlying tinnitus. However, due to the comorbidity of tinnitus and hearing loss, it has been difficult to differentiate between neural correlates of tinnitus and consequences of hearing loss. In this study, we dissociated tinnitus and hearing loss in FVB mice, which exhibit robust resistance to tinnitus following monaural noise-induced hearing loss. Furthermore, knock-down of glutamate decarboxylase 65 (GAD65) expression in auditory cortex (AI) by RNA interference gave rise to tinnitus in normal-hearing FVB mice. We found that tinnitus was significantly correlated with downregulation of GAD65 in the AI. By contrast, cortical map distortions, which have been hypothesized as a mechanism underlying tinnitus, were correlated with hearing loss but not tinnitus. Our findings suggest new strategies for the rehabilitation of tinnitus and other phantom sensation, such as phantom pain.SIGNIFICANCE STATEMENT Hearing loss is the biggest risk factor for tinnitus in humans. Most animal models of tinnitus also exhibit comorbid hearing loss, making it difficult to dissociate the mechanisms underlying tinnitus from mere consequences of hearing loss. Here we show that, although both C57BL/6 and FVB mice exhibited similar noise-induced hearing threshold increase, only C57BL/6, but not FVB, mice developed tinnitus following noise exposure. Although both strains showed frequency map reorganization following noise-induced hearing loss, only C57BL/6 mice had reduced glutamate decarboxylase 65 (GAD65) expression in the auditory cortex (AI). Knocking down GAD65 expression in the AI resulted in tinnitus in normal-hearing FVB mice. Our results suggest that reduced inhibitory neuronal function, but not sensory map reorganization, underlies noise-induced tinnitus.

Functional implications of Cav 2.3 R-type voltage-gated calcium channels in the murine auditory system - novel vistas from brainstem-evoked response audiometry.

Voltage-gated Ca2+ channels (VGCCs) are considered to play a key role in auditory perception and information processing within the murine inner ear and brainstem. In the past, Cav 1.3 L-type VGCCs gathered most attention as their ablation causes congenital deafness. However, isolated patch-clamp investigation and localization studies repetitively suggested that Cav 2.3 R-type VGCCs are also expressed in the cochlea and further components of the ascending auditory tract, pointing to a potential functional role of Cav 2.3 in hearing physiology. Thus, we performed auditory profiling of Cav 2.3+/+ controls, heterozygous Cav 2.3+/- mice and Cav 2.3 null mutants (Cav 2.3-/- ) using brainstem-evoked response audiometry. Interestingly, click-evoked auditory brainstem responses (ABRs) revealed increased hearing thresholds in Cav 2.3+/- mice from both genders, whereas no alterations were observed in Cav 2.3-/- mice. Similar observations were made for tone burst-related ABRs in both genders. However, Cav 2.3 ablation seemed to prevent mutant mice from total hearing loss particularly in the higher frequency range (36-42kHz). Amplitudegrowth function analysis revealed, i.a., significant reduction in ABR wave WI and WIII amplitude in mutant animals. In addition, alterations in WI -WIV interwave interval were observed in female Cav 2.3+/- mice whereas absolute latencies remained unchanged. In summary, our results demonstrate that Cav 2.3 VGCCs are mandatory for physiological auditory information processing in the ascending auditory tract.

Effects of frequency and duration of sound stimuli on hearing threshold increments among hearing-impaired individuals in Taiwan

This study investigated the effects of hearing type (with or without earphones) and sound stimulus exposure duration (90 s, 105 s, and 120 s) on increments in the hearing threshold with sound stimulation at various frequencies (125 Hz, 1,000 Hz, and 6,000 Hz), using an ascending run, in 48 hearing-impaired individuals. A 2 (hearing type) × 3 (sound stimulus exposure duration) × 3 (frequency of stimulus noise) repeated-measures design and an ascending method of limits was used in the experiment. Increments of the hearing threshold of the participants were analyzed using three-way repeated-measures analysis of variance. We found that the increase in hearing threshold was significant when participants wore earphones than when they did not. The hearing threshold increment was higher when the duration of sound exposure was 120 s and 105 s than when it was 90 s; moreover, the increment in the hearing threshold for a sound exposure duration of 105 s was less than that for 120 s. The frequency of the sound stimulus also affected increments in the hearing threshold: 1000 Hz was associated with a larger hearing threshold increment than were 125 Hz and 6000 Hz; however, there was no difference in the hearing threshold between 125 Hz and 6000 Hz stimuli. Our findings have implications for design of products for the hearing-impaired, for example, the design of card-sensing sounds and siren sounds, which are related to safety issues.

The Sub-acute Effect of Lead Exposure on the Auditory Brainstem Response in Male Rats

Background: Lead is a major environmental pollutant and can adversely affect humans and animals. There are conflicting data about the ototoxic effect of lead. This study experimentally examined the association between blood lead levels (BLL) and the subsequent hearing impairment in male rats. Methods: Twenty-two male rats were randomly categorized into experimental (exposed to lead acetate, 4 mg/kg by gavage) and control groups. We evaluated the groups by click and tone audiometric burst tests, comparing the data before and 30 days after exposure to lead acetate (4mg/kg). Also, blood samples were collected from the rats and analyzed for lead levels by graphite furnace atomic absorption spectrometry. Results: The study findings demonstrated remarkable increase in hearing threshold in the lead-exposed group, compared to the controls (p<0.0001). Also, the blood lead levels revealed a significant association of lead acetate with the hearing loss in rats. Conclusion: This study revealed that exposure to lead acetate can be damaging to hearing. However, future research is recommended to clarify the mechanism of action of lead toxicity on the auditory function at varying blood lead concentrations.

Stem Cell Based Drug Delivery for Protection of Auditory Neurons in a Guinea Pig Model of Cochlear Implantation.

Background: The success of a cochlear implant (CI), which is the standard therapy for patients suffering from severe to profound sensorineural hearing loss, depends on the number and excitability of spiral ganglion neurons (SGNs). Brain-derived neurotrophic factor (BDNF) has a protective effect on SGNs but should be applied chronically to guarantee their lifelong survival. Long-term administration of BDNF could be achieved using genetically modified mesenchymal stem cells (MSCs), but these cells should be protected – by ultra-high viscous (UHV-) alginate (‘alginate-MSCs’) – from the recipient immune system and from uncontrolled migration.Methods: Brain-derived neurotrophic factor-producing MSCs were encapsulated in UHV-alginate. Four experimental groups were investigated using guinea pigs as an animal model. Three of them were systemically deafened and (unilaterally) received one of the following: (I) a CI; (II) an alginate-MSC-coated CI; (III) an injection of alginate-embedded MSCs into the scala tympani followed by CI insertion and alginate polymerization. Group IV was normal hearing, with CI insertion in both ears and a unilateral injection of alginate-MSCs. Using acoustically evoked auditory brainstem response measurements, hearing thresholds were determined before implantation and before sacrificing the animals. Electrode impedance was measured weekly. Four weeks after implantation, the animals were sacrificed and the SGN density and degree of fibrosis were evaluated.Results: The MSCs survived being implanted for 4 weeks in vivo. Neither the alginate-MSC injection nor the coating affected electrode impedance or fibrosis. CI insertion with and without previous alginate injection in normal-hearing animals resulted in increased hearing thresholds within the high-frequency range. Low-frequency hearing loss was additionally observed in the alginate-injected and implanted cochleae, but not in those treated only with a CI. In deafened animals, the alginate-MSC coating of the CI significantly prevented SGN from degeneration, but the injection of alginate-MSCs did not.Conclusion: Brain-derived neurotrophic factor-producing MSCs encapsulated in UHV-alginate prevent SGNs from degeneration in the form of coating on the CI surface, but not in the form of an injection. No increase in fibrosis or impedance was detected. Further research and development aimed at verifying long-term mechanical and biological properties of coated electrodes in vitro and in vivo, in combination with chronic electrical stimulation, is needed before the current concept can be tested in clinical trials.

Cav3.2 T-Type Calcium Channels Are Physiologically Mandatory for the Auditory System

Voltage-gated Ca2+ channels (VGCCs) play key roles in auditory perception and information processing within the inner ear and brainstem. Pharmacological inhibition of low voltage-activated (LVA) T-type Ca2+ channels is related to both age- and noise induced hearing loss in experimental animals and may represent a promising approach to the treatment of auditory impairment of various etiologies. Within the LVA Ca2+ channel subgroup, Cav3.2 is the most prominently expressed T-type channel entity in the cochlea and auditory brainstem. Thus, we performed a complete gender specific click and tone burst based auditory brainstem response (ABR) analysis of Cav3.2+/- and Cav3.2-/- mice, including i.a. temporal progression in hearing loss, amplitude growth function and wave latency analysis as well as a cochlear qPCR based evaluation of other VGCCs transcripts. Our results, based on a self-programmed automated wavelet approach, demonstrate that both heterozygous and Cav3.2 null mutant mice exhibit age-dependent increases in hearing thresholds at 5 months of age. In addition, complex alterations in WI-IV amplitudes and latencies were detected that were not attributable to alterations in the expression of other VGCCs in the auditory tract. Our results clearly demonstrate the important physiological role of Cav3.2 VGCCs in the spatiotemporal organization of auditory processing in young adult mice and suggest potential pharmacological targets for interventions in the future.

Hearing as an Independent Predictor of Postural Balance in 1075 Patients Evaluated for Dizziness

To evaluate the association between hearing and postural balance. Retrospective cross-sectional study. Tertiary care otolaryngology clinic. Patients examined for suspected vestibular disorder were included in this study. The outcome variable was postural sway measured by static posturography during quiet standing with eyes closed. The predictor variable was pure-tone average hearing threshold on the best hearing ear at 0.5, 1, 2, and 3 kHz. Covariates were age, sex, and vestibular disease or vestibular asymmetry assessed by bithermal caloric irrigation. In total, 1075 patients were included. Increased hearing threshold was a strong predictor of increased postural sway (path length) after correcting for age and sex. A 10-dB increase in hearing loss on the best hearing ear predicted a mean 6.0% increase in path length (confidence interval, 2.9%-9.3%, P < .001). Of the covariates, increasing age (P < .001) and male sex (P = .009) were significant predictors of increased postural sway. The effect of increased hearing threshold was also significant after adjusting for vestibular disease. Increased hearing threshold was an independent predictor of increased postural instability, and this effect was strongest for the best hearing ear. Unilateral vestibular disease did not seem to explain this association between hearing and postural balance. Reduced hearing is associated with impaired balance, and interventions to prevent falls should be considered for patients at risk.

Association between cadmium exposure and hearing impairment: a population-based study in Korean adults

BackgroundThe present study aimed to evaluate the clinical association between cadmium exposure and hearing impairment among the Korean population.MethodsThis retrospective cross-sectional study used the data obtained from the Korean National Health and Nutrition Examination Survey were used for our study. Finally, 3,228 participants were included in our study, which were then divided into quartiles based on their blood cadmium levels: first quartile (1Q), second quartile (2Q), third quartile (3Q), and fourth quartile (4Q) groups. The hearing thresholds were measured using an automatic audiometer at 0.5, 1, 2, 3, 4, and 6 kHz. Hearing loss (HL) was defined as >25 dB average hearing threshold (AHT).ResultsAll the groups had 807 participants each. The area under the receiver operating characteristic curves of cadmium level for HL were 0.634 (95% confidence interval [CI], 0.621–0.646). The participants in the 4Q group had higher Low/Mid-Freq, High-Freq, and AHT values than those in the other groups in the multivariate analysis after adjusting for confounding factors. The logistic regression showed that the OR for HL per 1 µg/L increase in cadmium was 1.25 (95% CI, 1.09–1.44; p=0.002) on the multivariate analysis. Moreover, the multivariate logistic regression analyses revealed that the participants in the 4Q group exhibited a 1.59-, 1.38-, and 1.41-fold higher odds for HL than those in the 1Q, 2Q, and 3Q groups, respectively. ConclusionHigh cadmium level quartile was associated with increased hearing thresholds and HL among the Korean adult population.

Functional Age-Related Changes Within the Human Auditory System Studied by Audiometric Examination.

Age related hearing loss (presbycusis) is one of the most common sensory deficits in the aging population. The main subjective ailment in the elderly is the deterioration of speech understanding, especially in a noisy environment, which cannot solely be explained by increased hearing thresholds. The examination methods used in presbycusis are primarily focused on the peripheral pathologies (e.g., hearing sensitivity measured by hearing thresholds), with only a limited capacity to detect the central lesion. In our study, auditory tests focused on central auditory abilities were used in addition to classical examination tests, with the aim to compare auditory abilities between an elderly group (elderly, mean age 70.4 years) and young controls (young, mean age 24.4 years) with clinically normal auditory thresholds, and to clarify the interactions between peripheral and central auditory impairments. Despite the fact that the elderly were selected to show natural age-related deterioration of hearing (auditory thresholds did not exceed 20 dB HL for main speech frequencies) and with clinically normal speech reception thresholds (SRTs), the detailed examination of their auditory functions revealed deteriorated processing of temporal parameters [gap detection threshold (GDT), interaural time difference (ITD) detection] which was partially responsible for the altered perception of distorted speech (speech in babble noise, gated speech). An analysis of interactions between peripheral and central auditory abilities, showed a stronger influence of peripheral function than temporal processing ability on speech perception in silence in the elderly with normal cognitive function. However, in a more natural environment mimicked by the addition of background noise, the role of temporal processing increased rapidly.

Effects of impulse noise from small arms on the organ of hearing when anti-noise devices are used

Relevance. The basis of modern rationing of noise and assessing its safety is the principle of equal energy: regardless of the source, effects are equal. However, this approach is not valid for impulse noise reaching the external auditory canal through the means of individual hearing protection. This issue needs further research.Intention. To assess effects of impulse noise when anti-noise devices are used on the auditory sensitivity and safety of military personnel.Methods. Effects of impulse noise of equal energy without anti-noise devices and reaching the external auditory canal through the means of protection was carried out in two groups of volunteers aged 18–23 years without contraindications for working under noise conditions. Shooters from the 1st group (12 persons) fired from an AK74M assault rifle (150 shots) in a free acoustic field. Shooters from the 2nd group (13 persons) used 6M2 noise protection headsets when shooting (330 shots).Results and discussion. The equivalent level of impulse noise affecting the hearing organ of the shooters from both study groups amounted to 99.4 dBA. Impulse noise filtering through a 6M2 noise protection headset led to a shift in the noise spectrum to the low-frequency region, therefore the maximum increase in hearing thresholds was noted not at high (as without anti-noise devices), but at low frequencies – 250 and 500 Hz. At the same time, the hearing thresholds restored after shooting without anti-noise devices within a day, and after shooting with noise protection headsets – in two hours.Conclusion. It was established that the impulse noise from small arms of the same equivalent level when reaching the external auditory canal through the anti-noise headphones is less dangerous in terms of hearing restoration than after direct exposure.

The association between obesity, diet quality and hearing loss in older adults.

Background: With the aging population, the prevalence of age-related hearing loss will increase substantially. Prevention requires more knowledge on modifiable risk factors. Obesity and diet quality have been suggested to play a role in the etiology of age-related hearing loss. We aimed to investigate independent associations of body composition and diet quality with age-related hearing loss.Methods: We performed cross-sectional and longitudinal analyses (follow-up: 4.4 years) in the population-based Rotterdam Study. At baseline (2006-2014), 2,906 participants underwent assessment of body composition, diet, and hearing. Of these 2,906 participants, 636 had hearing assessment at follow-up (2014-2016). Association of body composition and of diet quality with hearing loss were examined using multivariable linear regression models.Results: Cross-sectionally, higher body mass index and fat mass index were associated with increased hearing thresholds. These associations did not remain statistically significant at follow-up. We found no associations between overall diet quality and hearing thresholds.Conclusions: This study shows that a higher body mass index, and in particular a higher fat mass index, is related to age-related hearing loss. However, whether maintaining a healthy body composition may actually reduce the effects of age-related hearing loss in the aging population requires further longitudinal population-based research.

Effect of Combined Exposure to Noise and Vibration on Hearing.

Aim:This study was conducted to examine the effect(s) of combined exposure to whole-body vibration (WBV) and noise in railway workers.Methods:In this historical cohort study, train drivers with combined exposure to WBV and impermissible noise as the case group (n = 85) and shunters with just exposure to impermissible noise as the control group (n = 30) were recruited. The hearing threshold at the conventional audiometric frequencies was measured in both the groups, and the standard threshold shift (STS) and hearing threshold shift at higher frequencies were calculated. Data were analyzed by SPSS version 20 using t-test, Chi-square, and paired t-test.Results:There was no significant difference between the groups for age of participants as well as work duration and body mass index. Increased hearing threshold was most frequently observed at 3000, 4000, and 6000 Hz. STS and hearing threshold shift at high frequencies were observed at 6.0% and 3.3%, and 8.2% and 26.7% in train drivers and shunters in the left ear, respectively, but these were not statistically significant.Conclusion:Despite the unauthorized exposure to noise and WBV of train drivers, the STS and hearing threshold shift at higher frequencies were not more prevalent compared with the shunters who were exposed only to impermissible noise levels; hence, no association was found between noise and vibration in this study.

Longitudinal changes in hearing threshold levels for noise-exposed military personnel.

Military personnel are exposed to variable and sometimes very high noise in their professional environment. The aim of this study is to evaluate through a longitudinal study if our hearing conservation program has to be adapted to consider specific interventions for subgroups of our military population still subject to a higher risk of hearing loss. We conducted a retrospective longitudinal study in 2015-2016 to describe the evolution of hearing threshold levels of military personnel as measured during periodic audiometric screening over a period of 6years (2009-2014) after the implementation of our hearing conservation program. A linear mixed model explored the relationship of pure-tone average (PTA) on 3, 4 and 6KHz with probability of noise exposure, gender, age at baseline, time since baseline, hearing loss at baseline and ear. For 18,672 military individuals, our results show a small but statistically significant increase of 0.08dB per year in PTA on 3, 4 and 6KHz over the 6-year period that is consistently decelerating as a function of time. An additional annual increase of hearing thresholds due to higher age and moderate and high probability of exposure to noise was also found. No major adaptation of our hearing conservation program is required but efforts should be strengthened to better evaluate and counsel older individuals and subjects exposed to noise regarding avoidance of noise and correct use of personal hearing protection.

Loss of the Cochlear Amplifier Prestin Reduces Temporal Processing Efficacy in the Central Auditory System.

Active mechanical amplification of sound occurs in cochlear outer hair cells (OHCs) that change their length with oscillations of their membrane potential. Such length changes are the proposed cellular source of the cochlear amplifier, and prestin is the motor protein responsible for OHC electromotility. Previous findings have shown that mice lacking prestin displayed a loss of OHC electromotility, subsequent loss of distortion-product otoacoustic emissions, and a 40–60 dB increase in hearing thresholds. In this study we were interested in studying the functional consequences of the complete loss of cochlear amplification on neural coding of frequency selectivity, tuning, and temporal processing in the auditory midbrain. We recorded near-field auditory evoked potentials and multi-unit activity from the inferior colliculus (IC) of prestin (−/−) null and prestin (+/+) wild-type control mice and determined frequency response areas (FRAs), tuning sharpness, and gap detection to tone bursts and silent gaps embedded in broadband noise. We were interested in determining if the moderate to severe sensorineural hearing loss associated with the loss of motor protein prestin would also impair auditory midbrain temporal-processing measures, or if compensatory mechanisms within the brainstem could compensate for the loss of prestin. In prestin knockout mice we observed that there are severe impairments in midbrain tuning, thresholds, excitatory drive, and gap detection suggesting that brainstem and midbrain processing could not overcome the auditory processing deficits afforded by the loss of OHC electromotility mediated by the prestin protein.

Inner Ear Connexin Channels: Roles in Development and Maintenance of Cochlear Function.

Connexin 26 and connexin 30 are the prevailing isoforms in the epithelial and connective tissue gap junction systems of the developing and mature cochlea. The most frequently encountered variants of the genes that encode these connexins, which are transcriptionally coregulated, determine complete loss of protein function and are the predominant cause of prelingual hereditary deafness. Reducing connexin 26 expression by Cre/loxP recombination in the inner ear of adult mice results in a decreased endocochlear potential, increased hearing thresholds, and loss of >90% of outer hair cells, indicating that this connexin is essential for maintenance of cochlear function. In the developing cochlea, connexins are necessary for intercellular calcium signaling activity. Ribbon synapses and basolateral membrane currents fail to mature in inner hair cells of mice that are born with reduced connexin expression, even though hair cells do not express any connexin. In contrast, pannexin 1, an alternative mediator of intercellular signaling, is dispensable for hearing acquisition and auditory function.

Evaluation of Hearing in Children with Metabolic Syndrome.

The frequency of metabolic syndrome is increasing in both children and adults. In addition to metabolic complications such as obesity, hypertension, cardiovascular diseases, insulin resistance, and type 2 diabetes, metabolic syndrome may affect all systems of the body. The aim of the present study was to investigate the effect of metabolic syndrome on hearing in childhood. A prospective, controlled study was performed on 38 obese children diagnosed with metabolic syndrome and 34 healthy children. Anthropometric measurements and biochemical studies were performed. All individuals underwent pure-tone audiometry, tympanogram, and transient evoked otoacoustic emission (TEOAE) tests. The hearing thresholds of the patients were compared with healthy volunteers. There was no significant difference in terms of age and gender between the groups (p>0.05). There was no significant difference in mean hearing levels between the groups. When frequencies were compared, significantly increased hearing threshold levels were determined at low frequencies in children with metabolic syndrome. Analysis of the TEOAE results elicited no statistically significant variation in terms of signal-to-noise ratio values, signal amplitudes, or test reproducibility values between the study groups. Identification of the potential hearing losses early by means of detailed hearing examinations in children with metabolic syndrome is important. To the best of our knowledge, this is the first study to examine the effect of metabolic syndrome on hearing in this age group.

Risk Factors for increased hearing threshold in workers exposed to continuous and intermittent noise in the heavy equipment industry in North Jakarta

Noise exposure can cause hearing disorders. Both intensity and type of noise contribute to hearing impairment. Different noise types can have different auditory effects. This study aimed to compare changes in hearing thresholds between workers exposed to continuous and intermittent noise. This study employed heavy equipment industry workers at the fabrication and assembly department. Data collected from questionnaires and medical records included age, marital status, cumulative time worked, blood sugar level, blood pressure, smoking habit, hobbies, and results of an audiometric examination. Of total 167 workers, 15 (9%) showed increase in hearing threshold. Of these 15, 13 (86.7%) and 2 (13.3%) had been exposed to continuous and intermittent noise, respectively. Workers aged over 40 years had more than fourfold risk of having an increased hearing threshold. Those who had worked for more than 3.9 years were at high risk of having an increased hearing threshold. Those who were exposed to continuous noise had nearly fivefold risk of having an increased hearing threshold as compared to those exposed to intermittent noise. Workers who are aged over 40 years, have worked in the industry for numerous years, or have been exposed to continuous noise are at increased risk for hearing loss.

Effects of Occupational Metal Exposure on the Auditory System

Effects of Occupational Metal Exposure on the Auditory System

Fibroblast growth factor 12 is expressed in spiral and vestibular ganglia and necessary for auditory and equilibrium function

We investigated fibroblast growth factor 12 (FGF12) as a transcript enriched in the inner ear by searching published cDNA library databases. FGF12 is a fibroblast growth factor homologous factor, a subset of the FGF superfamily. To date, its localisation and function in the inner ear have not been determined. Here, we show that FGF12 mRNA is localised in spiral ganglion neurons (SGNs) and the vestibular ganglion. We also show that FGF12 protein is localised in SGNs, the vestibular ganglion, and nerve fibres extending beneath hair cells. Moreover, we investigated FGF12 function in auditory and vestibular systems using Fgf12-knockout (FGF12-KO) mice generated with CRISPR/Cas9 technology. Our results show that the inner ear morphology of FGF12-KO mice is not significantly different compared with wild-type mice. However, FGF12-KO mice exhibited an increased hearing threshold, as measured by the auditory brainstem response, as well as deficits in rotarod and balance beam performance tests. These results suggest that FGF12 is necessary for normal auditory and equilibrium function.