Effects of aging on brainstem responses to toneburst auditory stimuli: a cross-sectional and longitudinal study in dogs

Voxelwise analysis of the central hearing pathway in senior dogs reveals changes associated with fractional lifespan

Presbycusis, or age-related hearing loss, affects both elderly humans and dogs, significantly impairing their social interactions and cognition. In humans, presbycusis involves changes in peripheral and central auditory systems, with central changes potentially occurring independently. While peripheral presbycusis in dogs is well-documented, research on central changes remains limited. Diffusion tensor imaging (DTI) is a useful tool for detecting and quantifying cerebral white matter abnormalities. This study used DTI to explore the central auditory pathway of senior dogs, aiming to enhance our understanding of canine presbycusis. Dogs beyond 75% of their expected lifespan were recruited and screened with brainstem auditory evoked response testing to select dogs without severe peripheral hearing loss. Sixteen dogs meeting the criteria were scanned using a 3 T magnetic resonance scanner. Tract-based spatial statistics was used to analyze the central auditory pathways. A significant negative correlation between fractional lifespan and fractional anisotropy was found in the acoustic radiation, suggesting age-related white matter changes in the central auditory system. These changes, observed in dogs without severe peripheral hearing loss, may contribute to central presbycusis development.

Rapid hearing threshold assessment with modified auditory brainstem response protocols in dogs

Introduction

Auditory brainstem response (ABR) is the gold standard for hearing testing in dogs. ABR is commonly used in puppies to diagnose congenital sensorineural deafness. Long test times limit the use for a more comprehensive hearing screening in veterinary practice. This study aimed to establish a super-fast hearing screening protocol in dogs.

Methods

Hearing thresholds were routinely measured with a mobile device designed for newborn hearing screening in 90 dogs. We introduced modifications of the ABR protocol, e. g., a binaural test mode, higher stimulus rates, a broadband chirp stimulus, and an algorithm for automatic peak V detection in a stepwise fashion. Hearing thresholds were then measured with fast protocols utilizing either 30 Hz click or 90 Hz broadband chirp stimuli with 80, 60, 40, 30, 20, 10, 0 and -10 dBnHL stimulation intensities. Interrater reliability, agreement between click and chirp hearing thresholds and correlations with clinical characteristics of the dogs were assessed.

Results

Using all innovations, the test time for hearing threshold assessment in both ears was reduced to 1.11 min (mean). The chirp stimulus accentuated both, peak V and the subsequent trough, which are essential features for judgement of the hearing threshold, but preceding peaks were less conspicuous. Interrater reliability and agreement between click and chirp hearing threshold was excellent. Dogs >10 years of age and dogs with abnormal hearing score or otitis score had significantly higher hearing thresholds than younger dogs (p ≤ 0.001) or dogs without abnormalities (p < 0.001).

Conclusion

The results demonstrate that modifications in ABR protocols speed-up test times significantly while the quality of the recordings for hearing threshold assessment is maintained. Modified ABR protocols enable super-fast hearing threshold assessment in veterinary practice.

Determining Hearing Thresholds in Dogs Using the Staircase Method

There is a growing interest in performing playback experiments to understand which acoustical cues trigger specific behavioral/emotional responses in dogs. However, very limited studies have focused their attention on more basic aspects of hearing such as sensitivity, i.e., the identification of minimal intensity thresholds across different frequencies. Most previous studies relied on electrophysiological methods for audiograms for dogs, but these methods are considered less accurate than assessments based on behavioral responses. To our knowledge, only one study has established hearing thresholds using a behavioral assessment on four dogs but using a method that did not allow potential improvement throughout the sessions. In the present study, we devised an assessment procedure based on a staircase method. Implying the adaptation of the assessed intensity on the dogs' performance, this approach grants several assessments around the actual hearing threshold of the animal, thereby increasing the reliability of the result. We used such a method to determine hearing thresholds at three frequencies (0.5, 4.0, and 20.0 kHz). Five dogs were tested in each frequency. The hearing thresholds were found to be 19.5 ± 2.8 dB SPL at 0.5 kHz, 14.0 ± 4.5 dB SPL at 4.0 kHz, and 8.5 ± 12.8 dB SPL at 20.0 kHz. No improvement in performance was visible across the procedure. While the thresholds at 0.5 and 4.0 kHz were in line with the previous literature, the threshold at 20 kHz was remarkably lower than expected. Dogs' ability to produce vocalization beyond 20 kHz, potentially used in short-range communication, and the selective pressure linked to intraspecific communication in social canids are discussed as potential explanations for the sensitivity to higher frequencies.

Effect of audible static on blood pressure measurement by Doppler ultrasonic sphygmomanometry in cats

OBJECTIVES

The aim of the present study was to determine whether the use of headphones to eliminate audible static during Doppler ultrasonic sphygmomanometry affects blood pressure (BP) measurement in conscious young adult (aged 1-6 years) and mature adult/senior (aged ⩾7 years) cats.

METHODS

A randomized crossover study was conducted. Healthy client-owned cats (>1 year) were enrolled. Blood pressure measurements were obtained twice, 14 days apart, with or without the use of headphones worn by a veterinarian. A fear, anxiety and stress (FAS) score (0 = relaxed; 4 = severe signs) was recorded. A linear mixed-effects model was used to compare the effect of wearing headphones on BP measurement.

RESULTS

In total, 18 young adult and 14 mature adult and senior cats with a median age of 5 years (range 1-14 years) were enrolled. Of the cats, 47% (15/32) had an average BP measurement that was at least 10 mmHg higher when using headphones compared with when not using headphones, of which a majority (11/15, 73%) were young adult cats. The average BP measurement was not different when using headphones compared with when not using headphones (mean difference -7 mmHg; 95% confidence interval -14 to 0.6; P = 0.07). When compared within age groups, the average BP measurement taken when using headphones (125 ± 15 mmHg) was lower compared with the measurement taken when not using headphones (137 ± 17 mmHg) in young adult cats (P = 0.02).

CONCLUSIONS AND RELEVANCE

The reduction in the average BP measurement with the use of headphones suggests this method may be helpful in reducing situational hypertension, particularly in young adult cats. Our findings also highlight the importance of consistent use of headphones when comparing serial measurements in a cat.

Sound Localization Ability in Dogs

The minimum audible angle (MAA), defined as the smallest detectable difference between the azimuths of two identical sources of sound, is a standard measure of spatial auditory acuity in animals. Few studies have explored the MAA of dogs, using methods that do not allow potential improvement throughout the assessment, and with a very small number of dog(s) assessed. To overcome these limits, we adopted a staircase method on 10 dogs, using a two-forced choice procedure with two sound sources, testing angles of separation from 60° to 1°. The staircase method permits the level of difficulty for each dog to be continuously adapted and allows for the observation of improvement over time. The dogs’ average MAA was 7.6°, although with a large interindividual variability, ranging from 1.3° to 13.2°. A global improvement was observed across the procedure, substantiated by a gradual lowering of the MAA and of choice latency across sessions. The results indicate that the staircase method is feasible and reliable in the assessment of auditory spatial localization in dogs, highlighting the importance of using an appropriate method in a sensory discrimination task, so as to allow improvement over time. The results also reveal that the MAA of dogs is more variable than previously reported, potentially reaching values lower than 2°. Although no clear patterns of association emerged between MAA and dogs’ characteristics such as ear shape, head shape or age, the results suggest the value of conducting larger-scale studies to determine whether these or other factors influence sound localization abilities in dogs.

Relationship between hearing, cognitive function, and quality of life in aging companion dogs

Background

Elderly people with presbycusis are at higher risk for dementia and depression than the general population. There is no information regarding consequences of presbycusis in dogs.

Objective

Evaluate the relationship between cognitive function, quality of life, and hearing loss in aging companion dogs.

Animals

Thirty‐nine elderly companion dogs.

Methods

Prospective study. Hearing was evaluated using brainstem auditory evoked response (BAER) testing. Dogs were grouped by hearing ability. Owners completed the canine dementia scale (CADES) and canine owner‐reported quality of life (CORQ) questionnaire. Cognitive testing was performed, and cognitive testing outcomes, CADES and CORQ scores and age were compared between hearing groups.

Results

Nineteen dogs could hear at 50 dB, 12 at 70 dB, and 8 at 90 dB with mean ages (months) of 141 ± 14, 160 ± 16, and 172 ± 15 for each group respectively (P = .0002). Vitality and companionship CORQ scores were significantly lower as hearing deteriorated (6.6‐5.4, 50‐90 dB group, P = .03 and 6.9‐6.2, 50‐90 dB group, P = .02, respectively). Cognitive classification by CADES was abnormal in all 90 dB group dogs and normal in 3/12 70 dB group and 11/19 50 dB group dogs (P = .0004). Performance on inhibitory control, detour and sustained gaze tasks decreased significantly with hearing loss (P = .001, P = .008, P = .002, respectively). In multivariate analysis, higher CADES score was associated with worse hearing (P = .01).

Conclusions and Clinical Importance

Presbycusis negatively alters owner‐pet interactions and is associated with poor executive performance and owner‐assessed dementia severity.

Normative wideband acoustic immittance patterns for middle ear evaluation in dogs

The objective of this study was to investigate the clinical use of wideband acoustic immittance (WAI) reflectance for middle ear assessment in dogs. Otoscopy and brainstem auditory evoked response testing was performed on all dogs prior to the WAI assessment. Following calibration, dogs were comfortably restrained while the probe was placed into the ear canal to obtain recordings. Testing was repeated for replicability. Repeatable WAI reflectance patterns were observed in 24 dogs, characterized by low-reflectance resonant peaks at approximately 1500-1800 Hz and 3000-4000 Hz. Observed patterns suggest WAI may be a practical means of assessing middle ear function in dogs.

Early onset adult deafness in the Rhodesian Ridgeback dog is associated with an in-frame deletion in the EPS8L2 gene

Domestic dogs exhibit diverse types of both congenital and non-congenital hearing losses. Rhodesian Ridgebacks can suffer from a progressive hearing loss in the early stage of their life, a condition known as early onset adult deafness (EOAD), where they lose their hearing ability within 1–2 years after birth. In order to investigate the genetic basis of this hereditary hearing disorder, we performed a genome-wide association study (GWAS) by using a sample of 23 affected and 162 control Rhodesian Ridgebacks. We identified a genomic region on canine chromosome 18 (CFA18) that is strongly associated with EOAD, and our subsequent targeted Sanger sequencing analysis identified a 12-bp inframe deletion in EPS8L2 (CFA18:25,868,739–25,868,751 in the UMICH_Zoey_3.1/canFam5 reference genome build). Additional genotyping confirmed a strong association between the 12-bp deletion and EOAD, where all affected dogs were homozygous for the deletion, while none of the control dogs was a deletion homozygote. A segregation pattern of this deletion in a 2-generation nuclear family indicated an autosomal recessive mode of inheritance. Since EPS8L2 plays a critical role in the maintenance and integrity of the inner ear hair cells in humans and other mammals, the inframe deletion found in this study represents a strong candidate causal mutation for EOAD in Rhodesian Ridgebacks. Genetic and clinical similarities between childhood deafness in humans and EOAD in Rhodesian Ridgebacks emphasizes the potential value of this dog breed in translational research in hereditary hearing disorders.

Age-related positivity effect on behavioural responses of dogs to human vocalisations

Age-related changes in the brain can alter how emotions are processed. In humans, valence specific changes in attention and memory were reported with increasing age, i.e. older people are less attentive toward and experience fewer negative emotions, while processing of positive emotions remains intact. Little is yet known about this "positivity effect" in non-human animals. We tested young (n = 21, 1-5 years) and old (n = 19, >10 years) family dogs with positive (laugh), negative (cry), and neutral (hiccup, cough) human vocalisations and investigated age-related differences in their behavioural reactions. Only dogs with intact hearing were analysed and the selected sound samples were balanced regarding mean and fundamental frequencies between valence categories. Compared to young dogs, old individuals reacted slower only to the negative sounds and there was no significant difference in the duration of the reactions between groups. The selective response of the aged dogs to the sound stimuli suggests that the results cannot be explained by general cognitive and/or perceptual decline. and supports the presence of an age-related positivity effect in dogs, too. Similarities in emotional processing between humans and dogs may imply analogous changes in subcortical emotional processing in the canine brain during ageing.

Dog-assisted therapy in the dental clinic. Part B. Hazards and assessment of potential risks to the health and safety of the dental therapy dog

Background

A dental therapy dog may help anxious patients in the dental clinic overcome their fear and facilitate the completion of necessary dental care. Dental clinic activities are associated with hazards that may pose potential risks to the health and safety of the dental therapy dog.

Objectives

To describe potential hazards associated with risks to health and safety to therapy dogs in dental clinics and to present suggestions for risk minimisation by adopting best practices in dental clinic settings.

Materials and method

Literature searches in Medline, http://Clinicaltrials.gov, and Google Scholar for qualitative and quantitative assessments of occupational hazards and risks in dental clinics, in combination with a review of the reference list of the included studies. Identified hazards and risks were analysed relative to their relevance for the health and welfare of a therapy dog present in a dental clinic setting.

Results

Workplace hazards in the dental clinic that apply to both humans and therapy dogs are allergies, sharps injury, eye injury, stress, rhinitis, hearing impairment, and other hazards. Additional concerns associated with risks for the dental therapy dog are situations involving erratic patient behaviour and threats if the patient is an undisclosed disease carrier. Risks to the health and safety of the dental therapy dog in the clinics are present but are low if the dental clinical staff and dog handlers comply with best practices.

Conclusions

Best practice includes awareness amongst the clinic staff and the dog handler of all potential hazards in the dental clinic and on how to reduce these hazards as well as adverse events that may scare the dental therapy dog. The dental therapy dog team must be specially trained to work in a dental clinic. Each treatment session has to be exclusively tailored to that specific appointment and the individual patient.

Hearing disorders in cats

Practical relevance: Auditory function is a sense that is central to life for cats - being important in situational awareness of potential predators, pursuit of prey, and for communication with conspecifics, humans and other species. Deafness in cats is most frequently the result of a genetic disorder, strongly associated with white fur and blue eyes, but may also result from acquired causes such as advancing age, ototoxic drugs, infection, environmental noise and physical trauma. Deafness can be sensorineural, where there is loss of cochlear hair cells, or conductive, where sound is muffled on its way to the inner ear. Clinical challenges: Establishing whether a cat is deaf can be difficult as behavioral testing of hearing is subjective and does not reliably detect unilateral deafness. Brainstem auditory evoked response testing is an objective measure but is limited in its availability. Currently, sensorineural deafness is irreversible because no treatments are available to restore lost hair cells. Conductive hearing loss can usually be treated, although full hearing recovery following otitis media may take weeks as the body clears the middle ear of debris. Evidence base: The author draws on the published literature and his extensive research on clinical aspects and molecular genetics of deafness, principally in companion animals, to review types and forms of deafness in cats. He also discusses current diagnostic approaches and provides brief advice for managing cats with hearing loss.

Distortion product otoacoustic emissions in young adult and geriatric cats

Recordings of distortion product otoacoustic emissions (DPOAEs) were taken from 15 geriatric cats (mean age ± standard deviation, SD, 13.6 ± 2.7 years; range 10.2-19.4 years) and 12 young adult control cats (mean ± SD 4.6 ± 0.5 years; range 3.4-5 years) to identify frequency-specific age-related changes in cochlear responses. Recordings were performed for primary frequencies from 2 to 12 kHz in 2 kHz increments. Cats were considered to be geriatric > 11.9 ± 1.9 years of age. Brainstem auditory evoked response (BAER) recordings were also made for subjective comparison with DPOAE responses. No differences in DPOAE response amplitudes were observed at any tested frequency in geriatric cats compared to control cats, reflecting an apparent absence of loss of cochlear outer hair cells along the length of the cochlea. No linear regression relationships were found for DPOAE response amplitude versus age in geriatric cats, despite the progressive nature of age-related hearing loss in other species. The absence of reductions in response at any of the tested frequencies in cats within the age span where cats are considered to be geriatric indicates that age-related hearing loss, if it does develop in cats, begins later in the life span of cats than in dogs or human beings.

Role of antioxidants in prevention of age-related hearing loss: a review of literature

Age-related hearing loss (ARHL), also known as presbycusis, is one of the most prevalent chronic degenerative conditions. It is characterized by a decline in auditory function. ARHL is caused by the interaction of multiple factors, including cochlear aging, environment, genetic predisposition, and health comorbidities. The primary pathology of ARHL includes the hair cells loss, stria vascularis atrophy, and loss of spiral ganglion neurons as well as the changes in central auditory pathways. The research to date suggests that oxidative stress and mitochondrial DNA deletion (mtDNA) play a major role in pathophysiology of ARHL. Therefore, similar to other otological conditions, several studies have also showed that antioxidants can slow ARHL, but some also indicate that antioxidant therapy is not a magic elixir that will prevent or treat hearing loss associated with aging completely, but why? All available clinical trials, including animal and human studies, in English language that examined the protective effects of antioxidants against ARHL were reviewed. Materials were obtained by searching ELSEVIER, PubMed, Scopus, Web of knowledge, Google Scholar databases, Clinical trials, and Cochrane database of systematic reviews. Although ARHL has been shown to be slowed by supplementation with antioxidants, particularly in laboratory animals, a few studies have investigated the effect of interventions against ARHL in humans. High-quality clinical trials are needed to investigate if ARHL can be delayed or prevented in humans. However, it seems that targeting several cell-death pathways is better than targeting the only oxidative stress pathway.

Brainstem auditory-evoked potential in Boxer dogs

Brainstem auditory-evoked potential (BAEP) has been widely used for different purposes in veterinary practice and is commonly used to identify inherited deafness and presbycusis. In this study, 43 Boxer dogs were evaluated using the BAEP. Deafness was diagnosed in 3 dogs (2 bilateral and 1 unilateral) allowing the remaining 40 Boxers to be included for normative data analysis including an evaluation on the influence of age on the BAEP. The animals were divided into 2 groups of 20 Boxers each based on age. The mean age was 4.54 years (range, 1-8) in group I, and 9.83 years (range, 8.5-12) in group II. The mean latency for I, III, and V waves were 1.14 (±0.07), 2.64 (±0.11), and 3.48 (±0.10) ms in group I, and 1.20 (±0.12), 2.73 (±0.15), and 3.58 (±0.22) ms in group II, respectively. The mean inter-peak latencies for the I-III, III-V and I-V intervals were 1.50 (±0.15), 0.84 (±0.15), and 2.34 (±0.11) ms in group I, and 1.53 (±0.16), 0.85 (±0.15), and 2.38 (±0.19) ms in group II, respectively. Latencies of waves I and III were significant different between group I and II. For the I-III, III-V and I-V intervals, no significant differences were observed between the 2 groups. As far as we know, this is the first normative study of BAEP obtained from Boxer dogs.

An analysis of the inheritance pattern of an adult-onset hearing loss in Border Collie dogs

Background

During routine diagnostic BAER testing of dogs of various breeds for private owners at the Western College of Veterinary Medicine in Saskatoon, it became evident that some individual dogs developed hearing loss as adults. Although inherited congenital deafness has been widely reported in dogs, this type of deafness had not.

Findings

Special clinics were set up to screen working Border Collies at herding competitions. To determine the typical age that geriatric deafness might be expected, retired dogs were also recruited. Five of the 10 Border Collies 12 years of age or older had hearing loss (1 bilaterally deaf and 4 had reduced hearing). The adult onset deafness which exhibited in three families, did not usually occur until 5 years of age, too young to be geriatric deafness. This adult onset deafness fits an autosomal dominant pattern of inheritance. Several of these dogs had been BAER tested at younger ages with no sign of deafness. The deaf dogs were not associated with either gender. A survey was developed which was completed by the dog owners, that indicated that the hearing loss was gradual, not sudden. In addition, some family studies were conducted.

Conclusions

Dogs at 5 years of age were often in the prime of their herding careers and then did not respond appropriately to distant commands. This type of deafness is important to dog owners but is also a potential medical model for some forms of hearing loss in humans. This report also suggests that geriatric hearing loss is common in dogs older than 12 years.

Electronic supplementary material

The online version of this article (doi:10.1186/2052-6687-1-6) contains supplementary material, which is available to authorized users.

Brainstem auditory evoked potential testing in Dalmatian dogs in Brazil

The brain stem auditory-evoked potential (BAEP) is an electrophysiologic test that detects and records the electrical activity in the auditory system from cochlea to midbrain, generated after an acoustic stimulus applied to the external ear. The aim of this study is to obtain normative data for BAEP in Dalmatian dogs in order to apply this to the evaluation of deafness and other neurologic disorders. BAEP were recorded from 30 Dalmatian dogs for a normative Brazilian study. Mean latencies for waves I, III, and V were 1.14 (±0.09), 2.62 (±0.10), and 3.46 (±0.14) ms, respectively. Mean inter-peak latencies for I-III, III-V, and I-V intervals were 1.48 (±0.17), 0.84 (±0.12), and 2.31 (±0.18) ms, respectively. Unilateral abnormalities were found in 16.7% of animals and bilateral deafness was seen in one dog. The normative data obtained in this paper is compatible with other published data. As far as we know this is the first report of deafness occurrence in Dalmatian dogs in Brazil.

Use of a hearing loss grading system and an owner-based hearing questionnaire to assess hearing loss in pet dogs with chronic otitis externa or otitis media

BACKGROUND

Hearing loss is important when assessing the suitability of dogs with otitis externa/media for medical or surgical therapy.

HYPOTHESIS/OBJECTIVES

To assess an owner-completed questionnaire as an indicator of hearing loss and a canine hearing loss scoring system in chronic canine otitis.

ANIMALS

One hundred hospital population dogs referred for chronic otitis investigation.

METHODS

Owners completed a questionnaire to assess their dog's response to common household noises. The presence of otitis externa or media was determined and brainstem auditory-evoked response measurements were performed on each dog. The minimal hearing threshold (MHT) in decibels normal hearing level (dB NHL) was recorded and categorized according to the human World Health Organization grading system into five grades from 0 to 4 with cut-off values of ≤25 dB NHL, 26-40 dB NHL, 41-60 dB NHL, 60-80 dB NHL and ≥81 dB NHL.

RESULTS

The questionnaire correctly determined normal hearing in grade 0 cases, but did not reliably detect unilateral or grade 1 bilateral hearing loss. For dogs with bilateral hearing loss ≥ grade 2, questionnaire sensitivity was 83% [24 of 29, 95% confidence interval, (CI) 64-94%] and specificity was 94% (67 of 71, 95% CI 86-98%). Higher grades of hearing loss were significantly associated with the presence of otitis media (P < 0.01).

CONCLUSIONS AND CLINICAL IMPORTANCE

The questionnaire may be a useful in-practice screening tool in chronic canine otitis for moderate to severe bilateral hearing deficits (MHT ≥41 dB NHL). The hearing loss grading system may help clinicians make therapeutic decisions. Chronic otitis media may be associated with higher grades of hearing loss.

Estudo normativo e avaliação da influência da idade no potencial evocado auditivo em cães sem raça definida

O objetivo deste trabalho foi realizar estudo normativo dos potenciais evocados auditivos obtidos de 34 cães sem raça definida e avaliar a influência da idade nos resultados obtidos. Os animais foram divididos em dois grupos de diferentes faixas etárias e o potencial evocado auditivo foi realizado com um estímulo de 85dB. O grupo 1 incluiu 16 cães com idades entre um e oito anos e o grupo 2, 18 animais com idades acima de oito anos. O comprimento e o diâmetro da cabeça foram mensurados e não houve diferença estatística entre os dois grupos. No grupo 1, as médias das latências das ondas I, III e V foram: 1,13; 2,64 e 3,45ms; e dos intervalos I-III, III-V e I-V foram 1,51; 0,81 e 2,32ms, respectivamente. No grupo 2, as médias das latências das ondas I, III e V foram 1,15; 2,62 e 3,55ms; e dos intervalos I-III, III-V e I-V foram 1,47; 0,93 e 2,40ms, respectivamente. As latências observadas neste estudo foram semelhantes a estudos prévios realizados por outros autores. Nos grupos etários analisados e nas condições preestabelecidas deste estudo, a idade influenciou a latência da onda V e, consequentemente, modificou os intervalos III-V e I-V, portanto deve-se considerar essa variante na interpretação dos resultados do BAEP em cães.

Canine deafness

Conductive deafness, caused by outer or middle ear obstruction, may be corrected, whereas sensorineural deafness cannot. Most deafness in dogs is congenital sensorineural hereditary deafness, associated with the genes for white pigment: piebald or merle. The genetic cause has not yet been identified. Dogs with blue eyes have a greater likelihood of hereditary deafness than brown-eyed dogs. Other common forms of sensorineural deafness include presbycusis, ototoxicity, noise-induced hearing loss, otitis interna, and anesthesia. Definitive diagnosis of deafness requires brainstem auditory evoked response testing.

Variation in genes related to cochlear biology is strongly associated with adult-onset deafness in border collies

Domestic dogs can suffer from hearing losses that can have profound impacts on working ability and quality of life. We have identified a type of adult-onset hearing loss in Border Collies that appears to have a genetic cause, with an earlier age of onset (3–5 years) than typically expected for aging dogs (8–10 years). Studying this complex trait within pure breeds of dog may greatly increase our ability to identify genomic regions associated with risk of hearing impairment in dogs and in humans. We performed a genome-wide association study (GWAS) to detect loci underlying adult-onset deafness in a sample of 20 affected and 28 control Border Collies. We identified a region on canine chromosome 6 that demonstrates extended support for association surrounding SNP Chr6.25819273 (p-value = 1.09×10⁻¹³). To further localize disease-associated variants, targeted next-generation sequencing (NGS) of one affected and two unaffected dogs was performed. Through additional validation based on targeted genotyping of additional cases (n = 23 total) and controls (n = 101 total) and an independent replication cohort of 16 cases and 265 controls, we identified variants in USP31 that were strongly associated with adult-onset deafness in Border Collies, suggesting the involvement of the NF-κB pathway. We found additional support for involvement of RBBP6, which is critical for cochlear development. These findings highlight the utility of GWAS–guided fine-mapping of genetic loci using targeted NGS to study hereditary disorders of the domestic dog that may be analogous to human disorders.

The domestic dog offers a unique opportunity to study complex disorders similar to those seen in humans, but within the context of the much simpler genetic backgrounds of pure breeds, which represent closed populations. We performed a whole-genome search for genetic risk factors of adult-onset deafness in the Border Collie, a breed of herding dog that relies on acute hearing to perceive and respond to commands while working. Adult-onset deafness in Border Collies typically begins in early adulthood and is similar to age-related hearing loss in humans. This earlier onset has particular impact on the utility of working Border Collies and the livelihoods of their owners, and it appears to have a genetic cause. We identified three genetic variants that were strongly associated with adult-onset deafness in a sample of 405 Border Collies. These variants are located in two genes that have previously been linked to deafness, one involved in ear development and another that appears to mitigate tissue damage in the ear. These results provide new insight regarding genetic risk factors for age-related hearing loss in both dogs and humans.

Effect of middle ear effusion on the brain-stem auditory evoked response of Cavalier King Charles Spaniels

Brain-stem auditory evoked responses (BAER) were assessed in 23 Cavalier King Charles Spaniels with and without middle ear effusion at sound intensities ranging from 10 to 100 dB nHL. Significant differences were found between the median BAER threshold for ears where effusions were present (60 dB nHL), compared to those without (30 dB nHL) (P=0.001). The slopes of latency-intensity functions from both groups did not differ, but the y-axis intercept when the x value was zero was greater in dogs with effusions (P=0.009), consistent with conductive hearing loss. Analysis of latency-intensity functions suggested the degree of hearing loss due to middle ear effusion was 21 dB (95% confidence between 10 and 33 dB). Waves I-V inter-wave latency at 90 dB nHL was not significantly different between the two groups. These findings demonstrate that middle ear effusion is associated with a conductive hearing loss of 10-33 dB in affected dogs despite the fact that all animals studied were considered to have normal hearing by their owners.

Effects of aging on inner ear morphology in dogs in relation to brainstem responses to toneburst auditory stimuli

BACKGROUND

Age-related hearing loss (ARHL) is the most common form of hearing loss in humans and is increasingly recognized in dogs.

HYPOTHESIS

Cochlear lesions in dogs with ARHL are similar to those in humans and the severity of the histological changes is reflected in tone audiograms.

ANIMALS

Ten geriatric dogs (mean age: 12.7 years) and three 9-month-old dogs serving as controls for histological analysis.

METHODS

Observational study. Auditory thresholds were determined by recording brainstem responses (BERA) to toneburst auditory stimuli (1, 2, 4, 8, 12, 16, 24, and 32 kHz). After euthanasia and perfusion fixation, the temporal bones were harvested and processed for histological examination of the cochleas. The numbers of outer hair cells (OHCs) and inner hair cells (IHCs) were counted and the spiral ganglion cell (SGC) packing density and stria vascularis cross-sectional area (SVCA) were determined.

RESULTS

A combination of cochlear lesions was found in all geriatric dogs. There were significant reductions (P .001) in OHC (42%, 95% confidence interval [CI]; 24-64%) and IHC counts (21%, 95% CI; 62-90%) and SGC packing densities (323, 95% CI; 216-290) in the basal turn, SVCA was smaller in all turns. The greatest reduction in auditory sensitivity was at 8-32 kHz.

CONCLUSIONS AND CLINICAL IMPORTANCE

ARHL in this specific population of geriatric dogs was comparable histologically to the mixed type of ARHL in humans. The predominance of histological changes in the basal cochlear turn was consistent with the large threshold shifts observed in the middle- to high-frequency region.