Genetic and Environmental Factors in Age-Related Hearing Impairment

Genome-wide association study for age-related hearing loss in CFW mice

Age-related hearing impairment is the most common cause of hearing loss and is one of the most prevalent conditions affecting the elderly globally. It is influenced by a combination of environmental and genetic factors. The mouse and human inner ears are functionally and genetically homologous. Investigating the genetic basis of age-related hearing loss (ARHL) in an outbred mouse model may lead to a better understanding of the molecular mechanisms of this condition. We used Carworth Farms White (CFW) outbred mice, because they are genetically diverse and exhibit variation in the onset and severity of ARHL. The goal of this study was to identify genetic loci involved in regulating ARHL. Hearing at a range of frequencies was measured using Auditory Brainstem Response (ABR) thresholds in 946 male and female CFW mice at the age of 1, 6, and 10 months. We obtained genotypes at 4.18 million single nucleotide polymorphisms (SNP) using low-coverage (mean coverage 0.27x) whole-genome sequencing followed by imputation using STITCH. To determine the accuracy of the genotypes we sequenced 8 samples at >30x coverage and used calls from those samples to estimate the discordance rate, which was 0.45%. We performed genetic analysis for the ABR thresholds for each frequency at each age, and for the time of onset of deafness for each frequency. The SNP heritability ranged from 0 to 42% for different traits. Genome-wide association analysis identified several regions associated with ARHL that contained potential candidate genes, including Dnah11, Rapgef5, Cpne4, Prkag2, and Nek11. We confirmed, using functional study, that Prkag2 deficiency causes age-related hearing loss at high frequency in mice; this makes Prkag2 a candidate gene for further studies. This work helps to identify genetic risk factors for ARHL and to define novel therapeutic targets for the treatment and prevention of ARHL.

Recent advances and future challenges in gene therapy for hearing loss

Hearing loss is the most common sensory deficit experienced by humans and represents one of the largest chronic health conditions worldwide. It is expected that around 10% of the world's population will be affected by disabling hearing impairment by 2050. Hereditary hearing loss accounts for most of the known forms of congenital deafness, and over 25% of adult-onset or progressive hearing loss. Despite the identification of well over 130 genes associated with deafness, there is currently no curative treatment for inherited deafness. Recently, several pre-clinical studies in mice that exhibit key features of human deafness have shown promising hearing recovery through gene therapy involving the replacement of the defective gene with a functional one. Although the potential application of this therapeutic approach to humans is closer than ever, substantial further challenges need to be overcome, including testing the safety and longevity of the treatment, identifying critical therapeutic time windows and improving the efficiency of the treatment. Herein, we provide an overview of the recent advances in gene therapy and highlight the current hurdles that the scientific community need to overcome to ensure a safe and secure implementation of this therapeutic approach in clinical trials.

The association of food intake on the development of hearing impairment after middle age among Japanese community dwellers

OBJECTIVES

This study aimed to determine whether food intake modifies the risk of developing hearing impairment (HI) in Japanese adults in their 40s.

METHODS

Data for individuals who were in their 40s with no HI at baseline and had participated in the survey multiple times were extracted from the National Institute for Longevity Sciences, Longitudinal Study of Aging. A total of 1846 samples observed for up to 11.5 years in 421 participants were included in the analyses. The average 3-day food intake was calculated. HI is defined as a pure-tone average of the better ear at frequencies of 0.5, 1, 2, and 4 kHz greater than 25 dB. The risk of developing HI in the 18 food groups was calculated longitudinally using multivariable cumulative data analyses.

RESULTS

Even after adjusting basic confounding factors, food groups, and baseline hearing level, significant associations were found between beverage consumption and risk increments for HI (odds ratio [OR] = 2.374, 95% confidence interval [CI]:1.141-4.940) and also between mushroom intake and risk reduction (OR = 0.215, 95% CI:0.069-0.667). Other foods did not consistently show significant results when the combination of analysis variables were changed.

CONCLUSIONS

Although the effect of food on hearing is modest to the extent that the significance varies with the variables used in the analysis, the intake of beverages and mushrooms could potentially modify the risk of developing HI after middle age.

Large-scale phenotyping and characterization of age-related hearing loss in outbred CFW mice

Age-related hearing loss (ARHL), or presbycusis, is one of the most prevalent conditions affecting the global population. A substantial fraction of patients with ARHL have no identifiable mutation despite over a hundred having been discovered, suggesting unidentified monogenic or polygenic causes. In this study, we investigated the hearing function of the aging outbred CFW mice through auditory brainstem response (ABR) thresholds. Through the characterization of 1,132 ABRs, we observed significant variation in both absolute thresholds and the effect of aging. We identify eight distinct patterns of hearing loss and were able to categorize nearly all data within these eight categories. Proportions within each category varied immensely between aging timepoints. We observe a small but consistent hearing deficit in female CFW mice. The resulting phenotypic data are a necessity for ARHL association mapping at a higher resolution than has previously been achieved and provides a new resource for studying ARHL.

The influence of metabolic syndrome on age-related hearing loss from the perspective of mitochondrial dysfunction

With the increase in life expectancy in the global population, aging societies have emerged in many countries, including China. As a common sensory defect in the elderly population, the prevalence of age-related hearing loss and its influence on society are increasing yearly. Metabolic syndrome is currently one of the main health problems in the world. Many studies have demonstrated that metabolic syndrome and its components are correlated with a variety of age-related diseases of the peripheral sensory system, including age-related hearing loss. Both age-related hearing loss and metabolic syndrome are high-prevalence chronic diseases, and many people suffer from both at the same time. In recent years, more and more studies have found that mitochondrial dysfunction occurs in both metabolic syndrome and age-related hearing loss. Therefore, to better understand the impact of metabolic syndrome on age-related hearing loss from the perspective of mitochondrial dysfunction, we reviewed the literature related to the relationship between age-related hearing loss and metabolic syndrome and their components to discern the possible role of mitochondria in both conditions.

Visual and hearing impairment and their association with depression among middle-aged and older individuals in India: Evidence from a cross-sectional study

OBJECTIVE

The aim of the study was to determine the prevalence and associated factors of visual and hearing impairment as well as to investigate their association with depression among individuals aged 45 and above in India.

METHODS

The study utilized data from the Longitudinal Ageing Study in India (LASI) Wave 1, (2017-18). The total sample size of this study was 65,562 individuals aged 45 and above. Descriptive statistics along with bivariate and multivariable analyses were performed to fulfill the objectives.

RESULTS

The prevalence of visual impairment in the study population was 32.1 percent, whereas the prevalence of self-reported hearing impairment was 6.9 percent. In the logistic regression models, both visual impairment [Adjusted odds ratio (AOR)-1.06; 95% Confidence interval (CI):0.99-1.14] as well as hearing impairment [AOR-1.25; 95% CI:1.11-1.41] were found to be significantly associated with depression. Moreover, individuals with a single impairment were 8 percent [AOR-1.08; 95% CI: 1.01-1.16] and individuals with dual impairment were 36 percent [AOR-1.36; 95% CI:1.13-1.65] significantly more likely to have depression.

CONCLUSION

Individuals with sensory impairment were more likely to suffer from depression and the risk was significantly higher among individuals with dual impairment. Therefore, clinicians dealing with individuals with sensory impairments must be aware of the likelihood of comorbid depression in order to provide timely screening and treatment.

Hearing loss and tinnitus: association studies for complex-hearing disorders in mouse and man

Genome-wide association studies (GWAS) provide an unbiased first look at genetic loci involved in aging and noise-induced sensorineural hearing loss and tinnitus. The hearing phenotype, whether audiogram-based or self-report, is regressed against genotyped information at representative single nucleotide polymorphisms (SNPs) across the genome. Findings include the fact that both hearing loss and tinnitus are polygenic disorders, with up to thousands of genes, each of effect size of < 0.02. Smaller human GWAS' were able to use objective measures and identified a few loci; however, hundreds of thousands of participants have been required for the statistical power to identify significant variants, and GWAS is unable to assess rare variants with mean allele frequency < 1%. Animal studies are required as well because of inability to access the human cochlea. Mouse GWAS builds on linkage techniques and the known phenotypic differences in auditory function between inbred strains. With the advantage that the laboratory environment can be controlled for noise and aging, the Hybrid Mouse Diversity Panel (HDMP) combines 100 strains sequenced at high resolution. Lift-over regions between mice and humans have identified over 17,000 homologous genes. Since most significant SNPs are either intergenic or in introns, and binding sites between species are poorly preserved between species, expression quantitative trait locus information is required to bring humans and mice into agreement. Transcriptome-wide analysis studies (TWAS) can prioritize putative causal genes and tissues. Diverse species, each making a distinct contribution, carry a synergistic advantage in the quest for treatment and ultimate cure of sensorineural hearing difficulties.

Subjective Aging and Objectively Assessed Hearing Function: A Prospective Study of Older Adults

OBJECTIVES

Subjective aging is consistently related to a range of health-related outcomes, but little is known about its relationship with sensory functioning. The present prospective study tested whether subjective age and self-perceptions of aging (SPA) are associated with objective hearing function.

METHODS

Participants were 7,085 individuals aged 50-93 years (60% women, mean = 65.15, standard deviation [SD] = 8.71) from the Health and Retirement Study. Measures of subjective age, SPA, and information on demographic factors were obtained in 2008/2010. Objective hearing function was assessed 8 years later in 2016/2018. Furthermore, potential mediating variables (C-reactive protein, body mass index, physical inactivity, and chronic conditions) were assessed in 2012/2014.

RESULTS

In regression analyses that accounted for demographic factors, older subjective age and negative SPA were associated with lower hearing acuity 8 years later. In addition, 1 SD older subjective age and negative SPA were related to a 9% and 7% higher likelihood of hearing impairment. Mediation analyses revealed that physical inactivity and chronic conditions partially mediated subjective age and SPA associations with hearing acuity. There was little evidence that the link between subjective aging and hearing was moderated by hearing aids and partial support for a moderating role of age.

DISCUSSION

This study provides new evidence that subjective aging is prospectively related to hearing function. Individuals with older subjective age or negative SPA have unfavorable behavioral and clinical profiles that explain part of their lower hearing function. Individuals' experience with their aging process is a marker of risk for impaired hearing.

Age-Related Changes in the Cochlea and Vestibule: Shared Patterns and Processes

Both age-related hearing loss (ARHL) and age-related loss in vestibular function (ARVL) are prevalent conditions with deleterious consequences on the health and quality of life. Age-related changes in the inner ear are key contributors to both conditions. The auditory and vestibular systems rely on a shared sensory organ - the inner ear - and, like other sensory organs, the inner ear is susceptible to the effects of aging. Despite involvement of the same sensory structure, ARHL and ARVL are often considered separately. Insight essential for the development of improved diagnostics and treatments for both ARHL and ARVL can be gained by careful examination of their shared and unique pathophysiology in the auditory and vestibular end organs of the inner ear. To this end, this review begins by comparing the prevalence patterns of ARHL and ARVL. Next, the normal and age-related changes in the structure and function of the auditory and vestibular end organs are compared. Then, the contributions of various molecular mechanisms, notably inflammaging, oxidative stress, and genetic factors, are evaluated as possible common culprits that interrelate pathophysiology in the cochlea and vestibular end organs as part of ARHL and ARVL. A careful comparison of these changes reveals that the patterns of pathophysiology show similarities but also differences both between the cochlea and vestibular end organs and among the vestibular end organs. Future progress will depend on the development and application of new research strategies and the integrated investigation of ARHL and ARVL using both clinical and animal models.

Hearing Function: Identification of New Candidate Genes Further Explaining the Complexity of This Sensory Ability

To date, the knowledge of the genetic determinants behind the modulation of hearing ability is relatively limited. To investigate this trait, we performed Genome-Wide Association Study (GWAS) meta-analysis using genotype and audiometric data (hearing thresholds at 0.25, 0.5, 1, 2, 4, and 8 kHz, and pure-tone averages of thresholds at low, medium, and high frequencies) collected in nine cohorts from Europe, South-Eastern USA, Caucasus, and Central Asia, for an overall number of ~9000 subjects. Three hundred seventy-five genes across all nine analyses were tagged by single nucleotide polymorphisms (SNPs) reaching a suggestive p-value (p < 10⁻⁵). Amongst these, 15 were successfully replicated using a gene-based approach in the independent Italian Salus in the Apulia cohort (n = 1774) at the nominal significance threshold (p < 0.05). In addition, the expression level of the replicated genes was assessed in published human and mouse inner ear datasets. Considering expression patterns in humans and mice, eleven genes were considered particularly promising candidates for the hearing function: BNIP3L, ELP5, MAP3K20, MATN2, MTMR7, MYO1E, PCNT, R3HDM1, SLC9A9, TGFB2, and YTHDC2. These findings represent a further contribution to our understanding of the genetic basis of hearing function and its related diseases.

Association between NR3C1 gene polymorphisms and age-related hearing impairment in Qingdao Chinese elderly

BACKGROUND

Age-related hearing impairment (ARHI) has attracted increasing attention recently. It is caused by genetic and environmental factors. A number of ARHI-related genes have been found. This study aimed to detect the potential association between NR3C1 gene polymorphisms and ARHI by means of weighted allele score.

METHODS

A total of 861 participants from Qingdao city were selected by means of cluster random sampling. We statistically evaluated the characteristics of individuals and used the Mann-Whitney U test or chi-square test for comparison. The publicly available expression quantitative trait locus (eQTL) was queried on the website of the Genotype-Tissue Expression (GTEx). We used the weighted allele score and logistic regression analysis to explore the association between NR3C1 gene polymorphisms and ARHI. Finally, the prediction model was constructed by logistic regression and receiver operating characteristic (ROC) curve.

RESULTS

All individuals over 60 years of age were enrolled in this study. The allele of rs61757411, rs41423247 and rs6877893 were significantly different between the ARHI group and the normal hearing group (P < 0.01). Though eQTL analysis, rs6877893 and rs33388 might affect the occurrence of ARHI by affecting the expression of NR3C1 gene in artery aorta. Then we performed two models: one without adding any covariates into model and the other adjusting for demographic characteristic, smoking and drinking, diet and exercise, and physical conditions. In the multivariate-adjusted model 2, the odds ratio with 95% confidence interval for weighted allele score (NR3C1) was 0.841 (0.710-0.995, P = 0.043). The area under the ROC curve was 0.755, indicating that the model had good predictability.

CONCLUSIONS

Our study suggests that NR3C1 gene polymorphisms was significantly associated with ARHI.

A Genome-Wide Association Study of Age-Related Hearing Impairment in Middle- and Old-Aged Chinese Twins

Background

Age-related hearing impairment (ARHI) is considered an unpreventable disorder. We aimed to detect specific genetic variants that are potentially related to ARHI via genome-wide association study (GWAS).

Methods

A sample of 131 dizygotic twins was genotyped for single-nucleotide polymorphism- (SNP-) based GWAS. Gene-based test was performed using VEGAS2. Pathway enrichment analysis was conducted by PASCAL.

Results

The twins are with a median age of 49 years, of which 128 were females and 134 were males. rs6633657 was the only SNP that reached the genome-wide significance level for better ear hearing level (BEHL) at 2.0 kHz (P = 1.19 × 10^-8). Totally, 9, 10, 42, 7, 17, and 5 SNPs were suggestive evidence level for (P < 1 × 10^-5) BEHLs at 0.5, 1.0, 2.0, 4.0, and 8.0 kHz and pure tone average (PTA), respectively. Several promising genetic regions in chromosomes (near the C20orf196, AQPEP, UBQLN3, OR51B5, OR51I2, OR52D1, GLTP, GIT2, and PARK2) nominally associated with ARHI were identified. Gene-based analysis revealed 165, 173, 77, 178, 170, and 145 genes nominally associated with BEHLs at 0.5, 1.0, 2.0, 4.0, and 8.0 kHz and PTA, respectively (P < 0.05). For BEHLs at 0.5, 1.0, and 2.0 kHz, the main enriched pathways were phosphatidylinositol signaling system, regulation of ornithine decarboxylase, eukaryotic translation initiation factor (EIF) pathway, amine compound solute carrier (SLC) transporters, synthesis of phosphoinositides (PIPS) at the plasma membrane, and phosphatidylinositols (PI) metabolism.

Conclusions

The genetic variations reported herein are significantly involved in functional genes and regulatory domains that mediate ARHI pathogenesis. These findings provide clues for the further unraveling of the molecular physiology of hearing functions and identifying novel diagnostic biomarkers and therapeutic targets of ARHI.

Association of beta blocker use and hearing ability in adults: a cross-sectional study

OBJECTIVES

To investigate the potential association between beta blocker use and hearing ability in adults and to discern whether this effect is dose-dependent.

DESIGN

Cross-sectional analyses. Multiple linear regression was performed with hearing ability as the dependent variable and beta blocker use as the independent variable. The independent variable was classified into three dose categories for secondary analysis. Adjustments were made for age, gender, educational level, and tobacco smoking status.

STUDY SAMPLE

1636 adults, 75 of whom reported being on beta blockers, from the internet-based Netherlands Longitudinal Study on Hearing (NL-SH).

RESULTS

No significant association was found between beta blocker use and hearing ability in noise. In the adjusted regressions, beta blocker use changed the speech reception threshold in noise (SRT) by -0.04 dB signal-to-noise ratio (SNR) (95%CI [-0.67 to 0.58], p = 0.890). Medium dose beta blocker use changed SRT by -0.42 dB SNR (95%CI [-1.38 to 0.71], p = 0.433), while a high dose changed it by -0.26 dB SNR (95%CI [-1.74 to 1.4], p = 0.767).

CONCLUSIONS

No evidence was found for beta blocker-induced changes in hearing ability. Future studies on this topic should favour case-control and cohort study designs, while focussing on a hypertensive population to minimise confounding by indication.

The Influence of Aging, Hearing, and Tinnitus on the Morphology of Cortical Gray Matter, Amygdala, and Hippocampus

Age related hearing loss (presbycusis) is a natural process represented by elevated auditory thresholds and decreased speech intelligibility, especially in noisy conditions. Tinnitus is a phantom sound that also potentially leads to cortical changes, with its highest occurrence coinciding with the clinical onset of presbycusis. The aim of our project was to identify age, hearing loss and tinnitus related structural changes, within the auditory system and associated structures. Groups of subjects with presbycusis and tinnitus (22 subjects), with only presbycusis (24 subjects), young tinnitus patients with normal hearing (10 subjects) and young controls (17 subjects), underwent an audiological examination to characterize hearing loss and tinnitus. In addition, MRI (3T MR system, analysis in Freesurfer software) scans were used to identify changes in the cortical and subcortical structures. The following areas of the brain were analyzed: Heschl gyrus (HG), planum temporale (PT), primary visual cortex (V1), gyrus parahippocampus (PH), anterior insula (Ins), amygdala (Amg), and hippocampus (HP). A statistical analysis was performed in R framework using linear mixed-effects models with explanatory variables: age, tinnitus, laterality and hearing. In all of the cortical structures, the gray matter thickness decreased significantly with aging without having an effect on laterality (differences between the left and right hemispheres). The decrease in the gray matter thickness was faster in the HG, PT and Ins in comparison with the PH and V1. Aging did not influence the surface of the cortical areas, however there were differences between the surface size of the reported regions in the left and right hemispheres. Hearing loss caused only a borderline decrease of the cortical surface in the HG. Tinnitus was accompanied by a borderline decrease of the Ins surface and led to an increase in the volume of Amy and HP. In summary, aging is accompanied by a decrease in the cortical gray matter thickness; hearing loss only has a limited effect on the structure of the investigated cortical areas and tinnitus causes structural changes which are predominantly within the limbic system and insula, with the structure of the auditory system only being minimally affected.

Synergistic effect of smoking on age-related hearing loss in patients with diabetes

This study investigated the synergistic effects of risk factors on age-related hearing loss (ARHL) using nationwide cross-sectional data of 33,552 individuals from the 2010‒2013 Korea National Health and Nutrition Examination Survey. Patients with ARHL were selected based on their pure-tone audiometry results. Previously reported risk factors for ARHL were analyzed using logistic regression and propensity score-matching, and synergistic effects between risk factors were analyzed using propensity score-matching. Of the 12,570 individuals aged 40-79 years, 2002 (15.9%) met the criteria for ARHL. Male sex, exposure to occupational noise, and diabetes showed a significant relationship with ARHL (p < 0.05) in both the logistic regression and propensity score-matching analyses. Smoking and diabetes showed the strongest significant synergistic effect on ARHL (odds ratio [OR] 1.963, 95% confidence interval [CI] 1.285‒2.998; p = 0.002). In the subgroup analysis based on smoking status, current smokers with diabetes had a significant relationship with ARHL (OR 1.883, CI 1.191‒2.975; p = 0.009), whereas ex-smokers with diabetes did not (OR 1.250; CI 0.880‒1.775; p = 0.246). This implies that current smokers with diabetes may benefit from the cessation of smoking. In conclusion, patients with diabetes should strictly avoid or cease smoking to prevent the progression of ARHL.

Biological insights from multi-omic analysis of 31 genomic risk loci for adult hearing difficulty

Age-related hearing impairment (ARHI), one of the most common medical conditions, is strongly heritable, yet its genetic causes remain largely unknown. We conducted a meta-analysis of GWAS summary statistics from multiple hearing-related traits in the UK Biobank (n = up to 330,759) and identified 31 genome-wide significant risk loci for self-reported hearing difficulty (p < 5x10-8), of which eight have not been reported previously in the peer-reviewed literature. We investigated the regulatory and cell specific expression for these loci by generating mRNA-seq, ATAC-seq, and single-cell RNA-seq from cells in the mouse cochlea. Risk-associated genes were most strongly enriched for expression in cochlear epithelial cells, as well as for genes related to sensory perception and known Mendelian deafness genes, supporting their relevance to auditory function. Regions of the human genome homologous to open chromatin in epithelial cells from the mouse were strongly enriched for heritable risk for hearing difficulty, even after adjusting for baseline effects of evolutionary conservation and cell-type non-specific regulatory regions. Epigenomic and statistical fine-mapping most strongly supported 50 putative risk genes. Of these, 39 were expressed robustly in mouse cochlea and 16 were enriched specifically in sensory hair cells. These results reveal new risk loci and risk genes for hearing difficulty and suggest an important role for altered gene regulation in the cochlear sensory epithelium.

Identification of a novel mutation in CRYM in a Chinese family with hearing loss using whole-exome sequencing

Previous studies have identified ~50 genes that contribute to non-syndromic autosomal dominant sensorineural deafness (DFNA). However, in numerous families with hearing loss, the specific gene mutation remains to be identified. In the present study, the clinical characteristics and gene mutations were analyzed in a Chinese pedigree with hereditary hearing loss. The clinical characteristics of the family members were assessed and a detailed audiology function examination was performed. Whole-exome sequencing (WES) was performed to identify the gene mutation responsible for the hearing loss. Sanger sequencing was used to verify the candidate mutation detected in the family. The family consisted of 31 members, seven of whom were diagnosed with sensorineural deafness of varying degrees. No mutation was identified by the general deafness gene chip. However, a novel heterozygous mutation in exon 3 (c.152C>T; Pro51Leu) of the gene crystallin µ (CRYM) was identified by WES. This result was further verified by Sanger sequencing. Co-segregation of genotypes and phenotypes suggested that this novel mutation was instrumental for the hearing loss/DFNA. In conclusion, the present study identified a novel pathogenic mutation, NM_001888.5(CRYM): c.152C>T(Pro51Leu), associated with DFNA. This mutation has not been reported previously and further functional studies are warranted.

Diagnostic and therapeutic applications of genomic medicine in progressive, late-onset, nonsyndromic sensorineural hearing loss

The progressive, late-onset, nonsyndromic, sensorineural hearing loss (PNSHL) is the most common cause of sensory impairment globally, with presbycusis affecting greater than a third of individuals over the age of 65. The etiology underlying PNSHL include presbycusis, noise-induced hearing loss, drug ototoxicity, and delayed-onset autosomal dominant hearing loss (AD PNSHL). The objective of this article is to discuss the potential diagnostic and therapeutic applications of genomic medicine in PNSHL. Genomic factors contribute greatly to PNSHL. The heritability of presbycusis ranges from 25 to 75%. Current therapies for PNSHL range from sound amplification to cochlear implantation (CI). PNSHL is an excellent candidate for genomic medicine approaches as it is common, has well-described pathophysiology, has a wide time window for treatment, and is amenable to local gene therapy by currently utilized procedural approaches. AD PNSHL is especially suited to genomic medicine approaches that can disrupt the expression of an aberrant protein product. Gene therapy is emerging as a potential therapeutic strategy for the treatment of PNSHL. Viral gene delivery approaches have demonstrated promising results in human clinical trials for two inherited causes of blindness and are being used for PNSHL in animal models and a human trial. Non-viral gene therapy approaches are useful in situations where a transient biologic effect is needed or for delivery of genome editing reagents (such as CRISPR/Cas9) into the inner ear. Many gene therapy modalities that have proven efficacious in animal trials have potential to delay or prevent PNSHL in humans. The development of new treatment modalities for PNSHL will lead to improved quality of life of many affected individuals and their families.

Hearing Impairment in Old Age

BACKGROUND

Hearing impairment associated with old age (presbycusis) is becoming more common because the population is aging.

METHODS

This review is based on publications retrieved by a selective search in Medline and Google Scholar, including individual studies, meta-analyses, guidelines, Cochrane reviews, and other reviews.

RESULTS

The cardinal symptom of presbycusis is impaired communication due to bilateral hearing impairment. Patients may be unaware of the problem for a long time because of its insidious progression. Evidence suggests that untreated hearing impair- ment in old age can have extensive adverse effects on the patient's mental, physical, and social well-being. Early detection is possible with the aid of simple diagnostic tests or suitable questionnaires. In most cases, bilateral hearing aids are an effective treatment. Surgery is rarely indicated. For patients with uni- or bilateral deafness, a cochlear implant is the treatment of choice. These treatments can improve many patients' quality of life.

CONCLUSION

The small amount of evidence that is currently available suggests that presbycusis is underdiagnosed and under- treated in Germany. Early detection by physicians of all specialties, followed in each case by a specialized differential diagnostic evaluation, is a desirable goal.

Self-reported hearing loss questions provide a good measure for genetic studies: a polygenic risk score analysis from UK Biobank

Age-related hearing impairment (ARHI) is very common in older adults and has major impact on quality of life. The heritability of ARHI has been estimated to be around 50%. The present study aimed to estimate heritability and environmental contributions to liability of ARHI and the extent to which a polygenic risk score (PRS) derived from a recent genome-wide association study of questionnaire items regarding hearing loss using the UK Biobank is predictive of hearing loss in other samples. We examined (1) a sample from TwinsUK who have had hearing ability measured by pure-tone audiogram and the speech-to-noise ratio test as well as questionnaire measures that are comparable with the UK Biobank questionnaire items and (2) European and non-European samples from the UK Biobank which were not part of the original GWAS. Results indicated that the questionnaire items were over 50% heritable in TwinsUK and comparable with the objective hearing measures. In addition, we found very high genetic correlation (0.30-0.84) between the questionnaire responses and objective hearing measures in the TwinsUK sample. Finally, PRS computed from weighted UK Biobank GWAS results were predictive of both questionnaire and objective measures of hearing loss in the TwinsUK sample, as well as questionnaire-measured hearing loss in Europeans but not non-European subpopulations. These results demonstrate the utility of questionnaire-based methods in genetic association studies of hearing loss in adults and highlight the differences in genetic predisposition to ARHI by ethnic background.

Genetics of age-related hearing loss

Age-related hearing loss (ARHL) has recently been confirmed as a common complex trait, that is, it is heritable with many genetic variants each contributing a small amount of risk, as well as environmental determinants. Historically, attempts to identify the genetic variants underlying the ARHL have been of limited success, relying on the selection of candidate genes based on the limited knowledge of the pathophysiology of the condition, and linkage studies in samples comprising related individuals. More recently genome-wide association studies have been performed, but these require very large samples having consistent and reliable phenotyping for hearing loss (HL), and early attempts suffered from lack of reliable replication of their findings. Replicated variants shown associated with ARHL include those lying in genes GRM7, ISG20, TRIOBP, ILDR1, and EYA4. The availability of large biobanks and the development of collaborative consortia have led to a breakthrough over the last couple of years, and many new genetic variants associated with ARHL are becoming available, through the analysis publicly available bioresources and electronic health records. These findings along with immunohistochemistry and mouse models of HL look set to help disentangle the genetic architecture of ARHL, and highlight the need for standardization of phenotyping methods to facilitate data sharing and collaboration across research networks.

Increased oxidative stress, inflammation, and glutamate: Potential preventive and therapeutic targets for hearing disorders

Hearing disorders constitute one of the major health concerns in the USA. Decades of basic and clinical studies have identified numerous ototoxic agents and investigated their modes of action on the inner ear, utilizing tissue culture as well as animal and human models. Current preventive and therapeutic approaches are considered unsatisfactory. Therefore, additional modalities should be developed. Many studies suggest that increased levels of oxidative stress, chronic inflammation, and glutamate play an important role in the initiation and progression of damage to the inner ear leading to hearing impairments. To prevent these cellular deficits, antioxidants, anti-inflammatory agents, and antagonists of glutamate receptor have been used individually or in combination with limited success. It is essential, therefore, to simultaneously enhance the levels of antioxidant enzymes by activating the Nrf2 (a nuclear transcriptional factor) pathway, dietary and endogenous antioxidant compounds, and B12-vitamins in order to reduce the levels of oxidative stress, chronic inflammation, and glutamate at the same time. This review presents evidence to show that increased levels of these cellular metabolites, biochemical or factors are involved in the pathogenesis of cochlea leading to hearing impairments. It presents scientific rationale for the use of a mixture of micronutrients that may decrease the levels of oxidative damage, chronic inflammation, and glutamate at the same time. The benefits for using oral administration of proposed micronutrient mixture in humans are presented. Animal and limited human studies indirectly suggest that orally administered micronutrients can accumulate in the inner ear. Therefore, this route of administration may be useful in prevention, and in combination with standard care, in improved management of hearing problems following exposure to well-recognized and studied ototoxic agents, such as noise, cisplatin, aminoglycoside antibiotics, and advanced age.

Personality and Hearing Acuity: Evidence From the Health and Retirement Study and the English Longitudinal Study of Ageing

OBJECTIVE

Several determinants of age-related hearing impairment have been identified, but little is known about the predictive value of psychological factors. The present study examined whether five-factor model personality traits are prospectively associated with hearing acuity in middle-aged and older adults.

METHODS

Participants were adults aged 50 to 97 years (N > 10,000) drawn from the Health and Retirement Study (2012-2016) and the English Longitudinal Study of Ageing (2010-2014). In each sample, personality, demographic factors, health-related behaviors, body mass index, and memory function were assessed at baseline, and objective hearing acuity was measured 4 years later.

RESULTS

In both samples, higher conscientiousness and openness were associated with better hearing acuity and lower risk of impairment, whereas neuroticism was associated with a higher risk of hearing impairment. In the Health and Retirement Study and English Longitudinal Study of Ageing, respectively, 1 standard deviation (1-SD) higher conscientiousness, 1-SD higher openness, and 1-SD lower neuroticism were related to 13% to 10%, 8% to 6%, and 10% to 13% lower likelihoods of hearing impairment, respectively. In both samples, additional analyses revealed that physical activity and memory mediated the association between personality and hearing.

CONCLUSIONS

The present study provides robust evidence for an association between personality traits and hearing function. The findings broaden knowledge on risk and mitigating factors for age-related hearing impairment, which has implications for the quality of life of middle-aged and older adults.

Relationship between pure-tone audiogram findings and speech perception among older Japanese persons

OBJECTIVE

To clarify how the pure-tone threshold (PTT) on the PTA predicts speech perception (SP) in elderly Japanese persons.

METHODS

Data on PTT and SP were cross-sectionally analyzed in Japanese persons (656 ears in 353 patients, aged ≥65 years). Correlations of SP and average PTT in all tested frequencies were evaluated by Pearson's correlation coefficient and simple linear regression. After adjusting for sex, laterality of ears, and age, the relationship of average and frequency-specific PTT with impaired SP ≤50% was estimated by logistic regression models.

RESULTS

SP correlated well (r = -0.699) with the average PTT of all tested frequencies. On the other hand, the correlation between patient age and SP was weak, especially among ≤85-year-old persons (r = -0.092). Linear regression showed that the average PTT corresponding to SP of 50% was 76.4 dB nHL. Odds ratios for impaired SP were highest for PTT at 2000 Hz. Odds ratios were higher for middle (500, 1000, 2000 Hz) and high frequencies (4000, 8000 Hz) than low frequencies (125, 250 Hz).

CONCLUSION

The PTT on the pure-tone audiogram (PTA) is a good predictor of SP by speech audiometry among older persons, which could provide clinically important information for hearing aid fitting and cochlear implantation.

Genetic and Environmental Influences on Correlations Between Hearing and Cognitive Functions in Middle and Older Chinese Twins

The genetic and environmental impacts on correlations between hearing and cognitive functions have not been well studied. Cognitive function was evaluated by the Montreal Cognitive Assessment (MoCA). Hearing function was assessed by audiometric pure-tone hearing thresholds at different frequencies, including 0.5 kHz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, and 12.5 kHz, with the lower hearing thresholds indicating better hearing function. Cognitive and hearing functions were measured on 379 complete twin pairs (240 monozygotic and 139 dizygotic pairs) with a median age of 50 years (range: 40-80 years). Bivariate twin models were fitted to quantify the genetic and environmental components of the correlations between hearing and cognitive functions. The analysis showed significantly high genetic correlation between 2 kHz of hearing and cognition (r G = -1.00, 95% CI [-1.00, -0.46]) and moderate genetic correlation between 4 kHz of hearing and cognition (r G = -0.62, 95% CI [-1.00, -0.14]). We found no significant genetic correlations between low as well as high frequencies of hearing and cognition. Low to moderate common and unique environmental correlations were shown between low frequencies of hearing and cognition (-0.13 to -0.39) and the common environmental correlation between 8 kHz, one of the high frequencies of hearing, and cognition (-0.22). The middle frequencies of hearing and cognitive functions may have a shared genetic basis. Low frequencies of hearing and cognition may share similar common and unique environmental factors. At 8 kHz, the high frequency of hearing and cognition may share similar common environment. This twin study detected a significant genetic and environmental basis in the phenotype correlation between cognition and hearing, which differed across frequencies.

Dyslipidemia as a Potential Moderator of the Association between Hearing Loss and Depressive Symptoms

OBJECTIVES

Knowledge about moderation of the association between hearing loss and depression is scant. We investigated dyslipidemia as a potential moderator of the association between hearing/hearing loss and depressive symptoms.

DESIGN

Cross-sectional study.

SETTING

General population-based cohort in France (SU.VI.MAX 2; 2007-2009).

PARTICIPANTS

N= 4,307 adults (mean age = 61.5 ± 6.1 y; 59.6% women).

MEASUREMENTS

A score ≥ 16 on the Center for Epidemiologic Studies Depression Scale defined presence of depressive symptoms. Mean hearing level for each ear was defined as the pure-tone average of the following thresholds: 0.5, 1.0, 2.0 and 4.0 kHz; the value for the better hearing ear was retained for analysis. Hearing loss was defined as inability to hear at thresholds ≥ 25 dB in both ears. A subjective measure of perceived hearing loss was also used. Serum triglyceride, total-, LDL- and HDL-cholesterol concentrations were assessed in fasting blood samples and established cutoffs were used in multivariable logistic regression models. The interaction between hearing/hearing loss (independent variables) and each of the four lipid parameters was tested.

RESULTS

Even though the interaction tests regarding LDL-, HDL- cholesterol, and triglyceride status were statistically significant, the subgroup analyses revealed few significant and somewhat unexpected findings. In fact, among individuals with low LDL-cholesterol, unlike their counterparts with high LDL-cholesterol, there was an inverse association between hearing level in the better hearing ear and depressive symptoms (OR= 0.94; 95% CI: 0.89-0.99). Regarding the subjective measure of hearing, a few of the dyslipidemia-moderated associations were statistically significant, albeit not all in the predicted direction.

CONCLUSIONS

The findings provide some support for moderation of the association between hearing/hearing loss and depressive symptoms by dyslipidemia, with important lipid-specific and hearing measure-specific differences. The results could serve as impetus for future investigations in order to identify and target population subgroups with increased vulnerability to depression in the context of both sensory disability and aging.

Characterization of ATPase Activity of P2RX2 Cation Channel

P2X purinergic receptors are plasma membrane ATP-dependent cation channels that are broadly distributed in the mammalian tissues. P2RX2 is a modulator of auditory sensory hair cell mechanotransduction and plays an important role in hair cell tolerance to noise. In this study, we demonstrate for the first time in vitro and in cochlear neuroepithelium, that P2RX2 possesses the ATPase activity. We observed that the P2RX2 V60L human deafness mutation alters its ability to bind ATP, while the G353R has no effect on ATP binding or hydrolysis. A non-hydrolysable ATP assay using HEK293 cells suggests that ATP hydrolysis plays a significant role in the opening and gating of the P2RX2 ion channel. Moreover, the results of structural modeling of the molecule was in agreement with our experimental observations. These novel findings suggest the intrinsic ATPase activity of P2RX2 and provide molecular insights into the channel opening.