Metabolic and Sensory Components of Age-Related Hearing Loss

Global trends and burden of age-related hearing loss: 32-year study

BACKGROUND

Age-related hearing loss (ARHL) is a major cause of disability and diminished quality of life in older adults. This study uses data from the 2021 Global Burden of Disease (GBD) study to assess global ARHL.

METHODS

We evaluated ARHL prevalence, DALYs (Disability-Adjusted Life Years), ASPR (Age-Standardized Prevalence Rate), and ASDR (Age-Standardized DALYs Rate). Trend analysis was conducted using Estimated Annual Percentage Change (EAPC), with projections to 2050.

RESULT

From 1990 and 2021, global ARHL prevalence cases and DALYs increased by 109 %, reaching 1.55 billion and 44.45 million, respectively. The ASPR increased from 17,106.88 to 18,070.26, while the crude prevalence rate significantly from 13,890.66 to 19,587.14. Both ASPR and ASDR demonstrated significant age-related increases, particularly for moderate and moderately severe ARHL, with EAPC values of 1.39 and 1.49 for ASDR, respectively. Among individuals aged over 85 years, the ASPR of ARHL is expected to reach 80 %. Prevalence cases peaked in the 55-69 age group, with the highest number of cases (179.43 million) observed in the 55-59 subgroup. High-middle SDI regions and East Asia exhibited the most rapid growth. By 2050, ARHL cases are projected to reach 2.31 billion, with ASPR and ASDR expected to continue rising.

CONCLUSION

ARHL has increased globally over the past three decades, largely due to population aging. The burden is most severe in middle SDI regions, East Asia, and the 55-69 age group, primarily due to their substantial population bases. Addressing this escalating challenge requires enhanced public awareness, early screening initiatives, and targeted interventions.

Relationship between TyG-related index and hearing loss in people over 45 s in China

Background

Triglycerides and fasting glycemic index are biomarkers used to assess the risk of insulin resistance and metabolic syndrome. It and its derivatives such as the TyG-BMI index are currently able to reflect the degree of insulin resistance and are closely related to a variety of metabolic diseases. The relationship between the TyG-BMI index and hearing loss remains underexplored, particularly in the context of aging and public health. This study investigates the association of the TyG index, BMI index, and TyG-BMI index with hearing loss, with a focus on their potential implications for the aging population.

Methods

Data from the China Health and Retirement Longitudinal Study (CHARLS) database were analyzed using R software. We applied multi-factor logistic regression, linear regression, restricted cubic splines, and subgroup analyses to assess the impact of the TyG index, BMI index, and TyG-BMI index on hearing loss across different age groups.

Results

The TyG index was not significantly associated with hearing loss. However, both the BMI index and the TyG-BMI index exhibited a positive correlation with hearing loss, particularly among older individuals. The results suggest that as the population ages, higher BMI and TyG-BMI indices may increase the risk of hearing impairment.

Conclusion

While the TyG index does not show a significant link to hearing loss, higher BMI and TyG-BMI indices are associated with an increased risk of hearing loss, especially in older adults. These findings highlight the importance of considering aging-related factors in public health initiatives aimed at preventing hearing loss. Further research is needed to elucidate the mechanisms underlying these associations and to develop age-inclusive strategies for addressing hearing impairment in the aging population.

Large-scale audiometric phenotyping identifies distinct genes and pathways involved in hearing loss subtypes

Age-related hearing loss affects one-third of the population over 65 years. However, the diverse pathologies underlying these heterogenous phenotypes complicate genetic studies. To overcome challenges associated with accurate phenotyping for older adults with hearing loss, we applied computational phenotyping approaches based on audiometrically measured hearing loss. This novel phenotyping strategy uncovered distinct genetic variants associated with sensory and metabolic hearing loss. Sex-stratified analyses of these sexually dimorphic hearing loss phenotypes revealed a novel locus of relevance to sensory hearing loss in males, but not females. Enrichment analyses revealed that genes involved in frontotemporal dementia were implicated in metabolic hearing loss, while genes relating to sensory processing of sound by hair cells were implicated in sensory hearing loss. Our study has enhanced our understanding of these two distinct hearing loss phenotypes, representing the first step in the development of more precise treatments for these pathologically distinct hearing loss phenotypes.

Novel insights into mechanisms and therapeutics for presbycusis

Presbycusis, also referred to as age-related hearing loss, poses a substantial burden on both individuals and society. The hallmark of presbycusis is a progressive decrease in auditory sensitivity. Irreversible hearing loss occurs due to the limited regenerative capacity of spiral neurons and peripheral cochlear hair cells (HCs). Although hearing aids and cochlear implantations (CIs) are established approaches for alleviating symptoms of presbycusis, there are currently no preventive or curative measures available. This article provides a comprehensive discussion on the research progress pertaining to the classification, molecular mechanism, genetic susceptibility, as well as the applications and prospects of diverse therapeutic interventions of presbycusis. Building upon these discussions, promising interventions like gene therapy and stem cell (SC) therapy are proposed for their potential value in restoring cochlear function; thus aiming to pave new avenues for prevention and cure of presbycusis.

Executive Function Associations With Audibility-Adjusted Speech Perception in Noise

PURPOSE

Speech recognition in noise is challenging for listeners and appears to require support from executive functions to focus attention on rapidly unfolding target speech, track misunderstanding, and sustain attention. The current study was designed to test the hypothesis that lower executive function abilities explain poorer speech recognition in noise, including among older participants with hearing loss who often exhibit diminished speech recognition in noise and cognitive abilities.

METHOD

A cross-sectional sample of 400 younger-to-older adult participants (19 to < 90 years of age) from the community-based Medical University of South CarolinaLongitudinal Cohort Study of Age-related Hearing Loss were administered tasks with executive control demands to assess individual variability in a card-sorting measure of set-shifting/performance monitoring, a dichotic listening measure of selective attention/working memory, sustained attention, and processing speed. Key word recognition in the high- and low-context speech perception-in-noise (SPIN) tests provided measures of speech recognition in noise. The SPIN scores were adjusted for audibility using the Articulation Index to characterize the impact of varied hearing sensitivity unrelated to reduced audibility on cognitive and speech recognition associations.

RESULTS

Set-shifting, dichotic listening, and processing speed each explained unique and significant variance in audibility-adjusted, low-context SPIN scores (ps < .001), including after controlling for age, pure-tone threshold average (PTA), sex, and education level. The dichotic listening and processing speed effect sizes were significantly diminished when controlling for PTA, indicating that participants with poorer hearing sensitivity were also likely to have lower executive function and lower audibility-adjusted speech recognition.

CONCLUSIONS

Poor set-shifting/performance monitoring, slow processing speed, and poor selective attention/working memory appeared to partially explain difficulties with speech recognition in noise after accounting for audibility. These results are consistent with the premise that distinct executive functions support speech recognition in noise.

Aging affects Mandarin speakers' understanding of focus sentences in quiet and noisy environments

INTRODUCTION

Older adults experiencing normal aging make up most patients seeking services at audiology clinics. While research acknowledges that the speech perception abilities of aging adults can be diminished in lower-level speech identification or discrimination, there is less concern about how aging affects higher-level speech understanding, particularly in tonal languages. This study aimed to explore the effects of aging on the comprehension of implied intentions conveyed through prosodic features in Mandarin focus sentences, both in quiet and noisy environments.

METHODS

Twenty-seven younger listeners (aged 17 to 26) and 27 older listeners (aged 58 to 77) participated in a focus comprehension task. Their task was to interpret SAVO (subject-adverbial-verb-object) sentences with five focus conditions (initial subject-focus, medial adverbial-focus, medial verb-focus, final object-focus, and neutral non-focus) across five background conditions: quiet, white noise (at 0 and -10-dB signal-to-noise ratios, SNRs), and competing speech (at 0 and -10-dB SNRs). Comprehension performances were analyzed based on accuracy rates, and underlying processing patterns were evaluated using confusion matrices.

RESULTS

Younger listeners consistently excelled across focus conditions in quiet settings, but their scores declined in white noise at the SNR of -10-dB. Older adults exhibited variability in scores across focus conditions but not in background conditions. They scored lower than their younger counterparts, with the highest scores observed in the comprehension of sentences featuring a medial adverbial-focus. Analysis of confusion matrices revealed that younger adults seldom mistook focus conditions, whereas older adults tended to comprehend the other focused items as medial adverbials.

CONCLUSIONS

Older listeners' performance reflects their over-reliance on top-down language knowledge, while their bottom-up acoustic processing decreases when interpreting Mandarin focus sentences. These findings provide evidence of active cognitive processing in prosody comprehension among aging adults and offer insights for diagnosing and intervening with speech disorders in clinical settings.

Polygenic Risk Score-Based Association Analysis Identifies Genetic Comorbidities Associated with Age-Related Hearing Difficulty in Two Independent Samples

PURPOSE

Age-related hearing loss is the most common form of permanent hearing loss that is associated with various health traits, including Alzheimer's disease, cognitive decline, and depression. The present study aims to identify genetic comorbidities of age-related hearing loss. Past genome-wide association studies identified multiple genomic loci involved in common adult-onset health traits. Polygenic risk scores (PRS) could summarize the polygenic inheritance and quantify the genetic susceptibility of complex traits independent of trait expression. The present study conducted a PRS-based association analysis of age-related hearing difficulty in the UK Biobank sample (N = 425,240), followed by a replication analysis using hearing thresholds (HTs) and distortion-product otoacoustic emissions (DPOAEs) in 242 young adults with self-reported normal hearing. We hypothesized that young adults with genetic comorbidities associated with age-related hearing difficulty would exhibit subclinical decline in HTs and DPOAEs in both ears.

METHODS

A total of 111,243 participants reported age-related hearing difficulty in the UK Biobank sample (> 40 years). The PRS models were derived from the polygenic risk score catalog to obtain 2627 PRS predictors across the health spectrum. HTs (0.25-16 kHz) and DPOAEs (1-16 kHz, L1/L2 = 65/55 dB SPL, F2/F1 = 1.22) were measured on 242 young adults. Saliva-derived DNA samples were subjected to low-pass whole genome sequencing, followed by genome-wide imputation and PRS calculation. The logistic regression analyses were performed to identify PRS predictors of age-related hearing difficulty in the UK Biobank cohort. The linear mixed model analyses were performed to identify PRS predictors of HTs and DPOAEs.

RESULTS

The PRS-based association analysis identified 977 PRS predictors across the health spectrum associated with age-related hearing difficulty. Hearing difficulty and hearing aid use PRS predictors revealed the strongest association with the age-related hearing difficulty phenotype. Youth with a higher genetic predisposition to hearing difficulty revealed a subclinical elevation in HTs and a decline in DPOAEs in both ears. PRS predictors associated with age-related hearing difficulty were enriched for mental health, lifestyle, metabolic, sleep, reproductive, digestive, respiratory, hematopoietic, and immune traits. Fifty PRS predictors belonging to various trait categories were replicated for HTs and DPOAEs in both ears.

CONCLUSION

The study identified genetic comorbidities associated with age-related hearing loss across the health spectrum. Youth with a high genetic predisposition to age-related hearing difficulty and other related complex traits could exhibit sub-clinical decline in HTs and DPOAEs decades before clinically meaningful age-related hearing loss is observed. We posit that effective communication of genetic risk, promoting a healthy lifestyle, and reducing exposure to environmental risk factors at younger ages could help prevent or delay the onset of age-related hearing difficulty at older ages.

The Stria Vascularis: Renewed Attention on a Key Player in Age-Related Hearing Loss

Age-related hearing loss (HL), or presbycusis, is a complex and heterogeneous condition, affecting a significant portion of older adults and involving various interacting mechanisms. Metabolic presbycusis, a type of age-related HL, is characterized by the dysfunction of the stria vascularis, which is crucial for maintaining the endocochlear potential necessary for hearing. Although attention on metabolic presbycusis has waned in recent years, research continues to identify strial pathology as a key factor in age-related HL. This narrative review integrates past and recent research, bridging findings from animal models and human studies, to examine the contributions of the stria vascularis to age-related HL. It provides a brief overview of the structure and function of the stria vascularis and then examines mechanisms contributing to age-related strial dysfunction, including altered ion transport, changes in pigmentation, inflammatory responses, and vascular atrophy. Importantly, this review outlines the contribution of metabolic mechanisms to age-related HL, highlighting areas for future research. It emphasizes the complex interdependence of metabolic and sensorineural mechanisms in the pathology of age-related HL and highlights the importance of animal models in understanding the underlying mechanisms. The comprehensive and mechanistic investigation of all factors contributing to age-related HL, including cochlear metabolic dysfunction, remains crucial to identifying the underlying mechanisms and developing personalized, protective, and restorative treatments.

Age-Related Deficits in Binaural Hearing: Contribution of Peripheral and Central Effects

Pure-tone audiograms often poorly predict elderly humans' ability to communicate in everyday complex acoustic scenes. Binaural processing is crucial for discriminating sound sources in such complex acoustic scenes. The compromised perception of communication signals presented above hearing threshold has been linked to both peripheral and central age-related changes in the auditory system. Investigating young and old Mongolian gerbils of both sexes, an established model for human hearing, we demonstrate age-related supra-threshold deficits in binaural hearing using behavioral, electrophysiological, anatomical, and imaging methods. Binaural processing ability was measured as the binaural masking level difference (BMLD), an established measure in human psychophysics. We tested gerbils behaviorally with "virtual headphones," recorded single-unit responses in the auditory midbrain and evaluated gross midbrain and cortical responses using positron emission tomography (PET) imaging. Furthermore, we obtained additional measures of auditory function based on auditory brainstem responses, auditory-nerve synapse counts, and evidence for central inhibitory processing revealed by PET. BMLD deteriorates already in middle-aged animals having normal audiometric thresholds and is even worse in old animals with hearing loss. The magnitude of auditory brainstem response measures related to auditory-nerve function and binaural processing in the auditory brainstem also deteriorate. Furthermore, central GABAergic inhibition is affected by age. Because the number of synapses in the apical turn of the inner ear was not reduced in middle-aged animals, we conclude that peripheral synaptopathy contributes little to binaural processing deficits. Exploratory analyses suggest increased hearing thresholds, altered binaural processing in the brainstem and changed central GABAergic inhibition as potential contributors.

Age-related changes in the zebrafish and killifish inner ear and lateral line

Age-related hearing loss (ARHL) is a debilitating disorder for millions worldwide. While there are multiple underlying causes of ARHL, one common factor is loss of sensory hair cells. In mammals, new hair cells are not produced postnatally and do not regenerate after damage, leading to permanent hearing impairment. By contrast, fish produce hair cells throughout life and robustly regenerate these cells after toxic insult. Despite these regenerative abilities, zebrafish show features of ARHL. Here, we show that aged zebrafish of both sexes exhibited significant hair cell loss and decreased cell proliferation in all inner ear epithelia (saccule, lagena, utricle). Ears from aged zebrafish had increased expression of pro-inflammatory genes and significantly more macrophages than ears from young adult animals. Aged zebrafish also had fewer lateral line hair cells and less cell proliferation than young animals, although lateral line hair cells still robustly regenerated following damage. Unlike zebrafish, African turquoise killifish (an emerging aging model) only showed hair cell loss in the saccule of aged males, but both sexes exhibit age-related changes in the lateral line. Our work demonstrates that zebrafish exhibit key features of auditory aging, including hair cell loss and increased inflammation. Further, our finding that aged zebrafish have fewer lateral line hair cells yet retain regenerative capacity, suggests a decoupling of homeostatic hair cell addition from regeneration following acute trauma. Finally, zebrafish and killifish show species-specific strategies for lateral line homeostasis that may inform further comparative research on aging in mechanosensory systems.

Predicting Atrophy of the Cochlear Stria Vascularis from the Shape of the Threshold Audiogram

Several lines of evidence have suggested that steeply sloping audiometric losses are caused by hair cell degeneration, while flat audiometric losses are caused by strial atrophy, but this concept has never been rigorously tested in human specimens. Here, we systematically compare audiograms and cochlear histopathology in 160 human cases from the archival collection of celloidin-embedded temporal bones at the Massachusetts Eye and Ear. The dataset included 106 cases from a prior study of normal-aging ears, and an additional 54 cases selected by combing the database for flat audiograms. Audiogram shapes were classified algorithmically into five groups according to the relation between flatness (i.e., SD of hearing levels across all frequencies) and low-frequency pure-tone average (i.e., mean at 0.25, 0.5, and 1.0 kHz). Outer and inner hair cell losses, neural degeneration, and strial atrophy were all quantified as a function of cochlear location in each case. Results showed that strial atrophy was worse in the apical than the basal half of the cochlea and was worse in females than in males. The degree of strial atrophy was uncorrelated with audiogram flatness. Apical atrophy was correlated with low-frequency thresholds and basal atrophy with high-frequency thresholds, and the former correlation was higher. However, a multivariable regression with all histopathological measures as predictors and audiometric thresholds as the outcome showed that strial atrophy was a significant predictor of threshold shift only in the low-frequency region, and, even there, the contribution of outer hair cell damage was larger.SIGNIFICANCE STATEMENT Cochlear pathology can only be assessed postmortem; thus, human cochlear histopathology is critical to our understanding of the mechanisms of hearing loss. Dogma holds that relative damage to sensory cells, which transduce mechanical vibration into electrical signals, versus the stria vascularis, the cellular battery that powers transduction, can be inferred by the shape of the audiogram, that is, down-sloping (hair cell damage) versus flat (strial atrophy). Here we quantified hair cell and strial atrophy in 160 human specimens to show that it is the degree of low-frequency hearing loss, rather than the audiogram slope, that predicts strial atrophy. Results are critical to the design of clinical trials for hearing-loss therapeutics, as current drugs target only hair cell, not strial, regeneration.

Reversal of an existing hearing loss by gene activation in Spns2 mutant mice

Hearing loss is highly heterogeneous, but one common form involves a failure to maintain the local ionic environment of the sensory hair cells reflected in a reduced endocochlear potential. We used a genetic approach to ask whether this type of pathology can be reversed, using the Spns2tm1a mouse mutant known to show this defect. By activating Spns2 gene transcription at different ages after the onset of hearing loss, we found that an existing auditory impairment can be reversed to give close to normal thresholds for an auditory brainstem response (ABR), at least at low to mid stimulus frequencies. Delaying the activation of Spns2 led to less effective recovery of ABR thresholds, suggesting that there is a critical period for intervention. Early activation of Spns2 not only led to improvement in auditory function but also to protection of sensory hair cells from secondary degeneration. The genetic approach we have used to establish that this type of hearing loss is in principle reversible could be extended to many other diseases using available mouse resources.

Metabolic decline in an insect ear: correlative or causative for age-related auditory decline?

One leading hypothesis for why we lose our hearing as we age is a decrease in ear metabolism. However, direct measurements of metabolism across a lifespan in any auditory system are lacking. Even if metabolism does decrease with age, a question remains: is a metabolic decrease a cause of age-related auditory decline or simply correlative? We use an insect, the desert locust Schistocerca gregaria, as a physiologically versatile model to understand how cellular metabolism correlates with age and impacts on age-related auditory decline. We found that auditory organ metabolism decreases with age as measured fluorometrically. Next, we measured the individual auditory organ's metabolic rate and its sound-evoked nerve activity and found no correlation. We found no age-related change in auditory nerve activity, using hook electrode recordings, and in the electrophysiological properties of auditory neurons, using patch-clamp electrophysiology, but transduction channel activity decreased. To further test for a causative role of the metabolic rate in auditory decline, we manipulated metabolism of the auditory organ through diet and cold-rearing but found no difference in sound-evoked nerve activity. We found that although metabolism correlates with age-related auditory decline, it is not causative. Finally, we performed RNA-Seq on the auditory organs of young and old locusts, and whilst we found enrichment for Gene Ontology terms associated with metabolism, we also found enrichment for a number of additional aging GO terms. We hypothesize that age-related hearing loss is dominated by accumulative damage in multiple cell types and multiple processes which outweighs its metabolic decline.

Probability Distributions for Associations Between Cognitive Screening and Pure-tone Thresholds in Older Adults

OBJECTIVES

Lower general cognitive function is frequently reported in older adults with elevated pure-tone thresholds. Here, we examined reason(s) for this association, including whether this relationship is dependent on the frequency range or extent of hearing loss and cognitive screening performance.

DESIGN

Linear regression was used to examine associations between better-ear pure-tone thresholds and Mini-Mental Status Exam (MMSE) performance in a cross-sectional sample of relatively healthy older adults (N = 508; 68% women, 60-89+ years; M age = 72). Quantile regression was also used to identify the ranges of 0.5 and 4.0 kHz thresholds and MMSE scores where these variables exhibited significant associations.

RESULTS

MMSE scores and pure-tone thresholds exhibited small but significant associations, particularly for better-ear 0.5 kHz thresholds. This hearing threshold and cognitive screening association was present among participants with better hearing, including the oldest older adults. There was limited evidence for mediating health condition effects on this association. An item analysis of the MMSE revealed that the MMSE and pure-tone threshold associations were largely due to the delayed recall item of the MMSE.

CONCLUSIONS

Together, the small effect results are consistent with the extant literature and suggest that there are multiple reasons for modest pure-tone threshold and cognitive screening performance associations.

Accurate phenotypic classification and exome sequencing allow identification of novel genes and variants associated with adult-onset hearing loss

Adult-onset progressive hearing loss is a common, complex disease with a strong genetic component. Although to date over 150 genes have been identified as contributing to human hearing loss, many more remain to be discovered, as does most of the underlying genetic diversity. Many different variants have been found to underlie adult-onset hearing loss, but they tend to be rare variants with a high impact upon the gene product. It is likely that combinations of more common, lower impact variants also play a role in the prevalence of the disease. Here we present our exome study of hearing loss in a cohort of 532 older adult volunteers with extensive phenotypic data, including 99 older adults with normal hearing, an important control set. Firstly, we carried out an outlier analysis to identify genes with a high variant load in older adults with hearing loss compared to those with normal hearing. Secondly, we used audiometric threshold data to identify individual variants which appear to contribute to different threshold values. We followed up these analyses in a second cohort. Using these approaches, we identified genes and variants linked to better hearing as well as those linked to worse hearing. These analyses identified some known deafness genes, demonstrating proof of principle of our approach. However, most of the candidate genes are novel associations with hearing loss. While the results support the suggestion that genes responsible for severe deafness may also be involved in milder hearing loss, they also suggest that there are many more genes involved in hearing which remain to be identified. Our candidate gene lists may provide useful starting points for improved diagnosis and drug development.

Inner-hair-cell induced hearing loss: A biophysical modeling perspective

In recent years, experimental studies have demonstrated that malfunction of the inner-hair cells and their synapse to the auditory nerve is a significant hearing loss (HL) contributor. This study presents a detailed biophysical model of the inner-hair cells embedded in an end-to-end computational model of the auditory pathway with an acoustic signal as an input and prediction of human audiometric thresholds as an output. The contribution of the outer hair cells is included in the mechanical model of the cochlea. Different types of HL were simulated by changing mechanical and biochemical parameters of the inner and outer hair cells. The predicted thresholds yielded common audiograms of hearing impairment. Outer hair cell damage could only introduce threshold shifts at mid-high frequencies up to 40 dB. Inner hair cell damage affects low and high frequencies differently. All types of inner hair cell deficits yielded a maximum of 40 dB HL at low frequencies. Only a significant reduction in the number of cilia of the inner-hair cells yielded HL of up to 120 dB HL at high frequencies. Sloping audiograms can be explained by a combination of gradual change in the number of cilia of inner and outer hair cells along the cochlear partition from apex to base.

Metabolic and Sensory Components of Age-Related Hearing Loss: Associations With Distortion- and Reflection-Based Otoacoustic Emissions

Age-related hearing loss is difficult to study in humans because multiple genetic and environmental risk factors may contribute to pathology and cochlear function declines in older adults. These pathologies, including degeneration of the stria vascularis, are hypothesized to affect outer hair cells responsible for active cochlear amplification of low-level sounds. Otoacoustic emission (OAE) measures are used to quantify the energy added to the traveling wave in cochlear amplification, which typically weakens with increased pure-tone thresholds and for older individuals. Thus, the current study evaluated two OAE measures for individuals with different components of age-related hearing loss. We examined two retrospective adult lifespan datasets (18 to 89+ years of age) from independent sites (Medical University of South Carolina and Boys Town National Research Hospital), which included demographics, noise history questionnaires, distortion-product otoacoustic emissions (DPOAE), and cochlear reflectance (CR). Metabolic and sensory estimates of age-related hearing loss were derived from the audiograms in each dataset, and then tested for associations with DPOAE and CR. The results showed that metabolic estimates increased for older participants and were associated with lower overall DPOAE and CR magnitudes across frequency (i.e., lower fitted intercepts). Sensory estimates were significantly higher for males, who reported more positive noise histories compared to females and were associated with steeper negative across-frequency slopes for DPOAEs. Although significant associations were observed between OAE configurations, DPOAEs appeared uniquely sensitive to metabolic estimates. The current findings suggest that distortion-based measures may provide greater sensitivity than reflection-based measures to the components of age-related hearing loss.

Investigating the characteristics of genes and variants associated with self-reported hearing difficulty in older adults in the UK Biobank

BACKGROUND

Age-related hearing loss is a common, heterogeneous disease with a strong genetic component. More than 100 loci have been reported to be involved in human hearing impairment to date, but most of the genes underlying human adult-onset hearing loss remain unknown. Most genetic studies have focussed on very rare variants (such as family studies and patient cohort screens) or very common variants (genome-wide association studies). However, the contribution of variants present in the human population at intermediate frequencies is hard to quantify using these methods, and as a result, the landscape of variation associated with adult-onset hearing loss remains largely unknown.

RESULTS

Here we present a study based on exome sequencing and self-reported hearing difficulty in the UK Biobank, a large-scale biomedical database. We have carried out variant load analyses using different minor allele frequency and impact filters, and compared the resulting gene lists to a manually curated list of nearly 700 genes known to be involved in hearing in humans and/or mice. An allele frequency cutoff of 0.1, combined with a high predicted variant impact, was found to be the most effective filter setting for our analysis. We also found that separating the participants by sex produced markedly different gene lists. The gene lists obtained were investigated using gene ontology annotation, functional prioritisation and expression analysis, and this identified good candidates for further study.

CONCLUSIONS

Our results suggest that relatively common as well as rare variants with a high predicted impact contribute to age-related hearing impairment and that the genetic contributions to adult hearing difficulty may differ between the sexes. Our manually curated list of deafness genes is a useful resource for candidate gene prioritisation in hearing loss.