Prevalence, heritability and genetic correlations of congenital sensorineural deafness and pigmentation phenotypes in the Border Collie

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.

De-novo and genome-wide meta-analyses identify a risk haplotype for congenital sensorineural deafness in Dalmatian dogs

Congenital sensorineural deafness (CSD) has been reported to affect up to 30% of Dalmatian dogs world-wide and while unilaterally deaf dogs can live a close to normal life, dogs suffering bilateral deafness are frequently euthanized. Extreme-white coat patterning as encoded by the gene Melanocyte Inducing Transcription Factor (MITF) has long been postulated as the major risk factor for CSD in the Dalmatian breed. While attempts to identify causative risk variants associated with CSD have been numerous, no genome-wide association study has positively identified MITF as a risk locus for either bilateral or unilateral deafness in the Dalmatian breed to date. In this study, we identified an association with CSD on CFA20 in the vicinity of MITF within Australian Dalmatian dogs. Although not genome-wide significant, the association signal was validated by reanalysing publicly available data and merging the wider data resource with the local data to improve statistical power. The merged data, representing three major global populations of Dalmatian dogs, enabled us to identify a single, well-defined genome-wide significant risk haplotype for CSD. The haplotype was formed by three genome-wide significant associated markers (BICF2G630233852T>C, BICF2G630233861T>C, BICF2G630233888G>A) on CFA20 with 62% of bilaterally deaf dogs homozygous for the risk haplotype (CCA), while 30% of bilaterally deaf and 45% of hearing dogs carried one copy of the risk haplotype. Animals homozygous or heterozygous for the low-risk haplotype were less likely to be unilaterally deaf. While the association between the risk haplotype and deafness is incomplete, animals homozygous for the risk haplotype were 10-times more likely to be bilaterally deaf. Although the underlying causative variants are yet to be discovered, results from this study can now assist with reducing deafness in Dalmatian dogs.

Canine coat pigmentation genetics: a review

Our understanding of canine coat colour genetics and the associated health implications is developing rapidly. To date, there are 15 genes with known roles in canine coat colour phenotypes. Many coat phenotypes result from complex and/or epistatic genetic interactions among variants within and between loci, some of which remain unidentified. Some genes involved in canine pigmentation have been linked to aural, visual and neurological impairments. Consequently, coat pigmentation in the domestic dog retains considerable ethical and economic interest. In this paper we discuss coat colour phenotypes in the domestic dog, the genes and variants responsible for these phenotypes and any proven coat colour-associated health effects.

Deafness in Australian Cattle Dogs associated to QTL on chromosome 20 in genome-wide association study analyses

Pigment-associated deafness is a common hereditary condition in a range of dog breeds. The aim of this study was to perform a genome-wide association analysis to investigate the genetic architecture of deafness in Australian Cattle Dogs. Genotypes for 104 757 polymorphisms in 216 dogs were available for analyses after quality control. A genomic relationship matrix was used in the mixed model analyses to account for polygenic effects, as we tested each polymorphism for its association with deafness, in a case/control experimental design. Three approaches were used to code the genotypes and test for additive, recessive and dominant SNP effects. The genome-wide association study analyses identified a clear association peak on CFA20, with the most significant SNPs on this chromosome (1.29 × 10^-4 ) in the vicinity of MITF. Variants in MITF have been associated with white pigmentation in dogs and with deafness in humans and other species, supporting the premise that canine deafness is associated with variants in or near this gene. A recessive inheritance for the peak in CFA20 is possible given the significant results in the recessive model; however, the estimated heritability was low (4.54 × 10^-5 ). Further validation, identification of variants and testing in other dog breeds are needed.

Congenital sensorineural deafness in Australian Cattle dogs in the UK: Prevalence and association with phenotype

The Australian Cattle dog (ACD) is one of many breeds predisposed to congenital sensorineural deafness (CSD). The objective of this study was to estimate CSD prevalence and investigate any association with phenotype in the ACD in the UK. The database of the authors' institution was searched for ACD puppies undergoing brainstem auditory evoked response (BAER) testing for CSD screening (1999-2019). Inclusion criteria were BAER performed at 4-10 weeks of age, testing of complete litters and available phenotypic data. The age, sex, coat and iris colour, presence and location of face and body patches, hearing status and BAER- determined parental hearing status of each puppy were recorded. A multivariable mixed-effects logistic regression model was used to calculate odds ratios and 95% confidence intervals to determine whether any of these variables were significantly associated with CSD, while adjusting for clustering at litter level. Inclusion criteria were met for 524 puppies. Hearing was bilaterally normal in 464 puppies (88.6%). The prevalence of unilateral and bilateral CSD was 9.7% and 1.7%, respectively. On the basis of multivariable analysis, the presence of a pigmented face patch was the only phenotypic variable significantly associated with CSD, and was linked to a reduced risk of the condition. The prevalence was similar to that reported in an Australian population of ACDs. The key findings from this study were that overall CSD prevalence in the ACD population in the UK was 11.4%, and puppies with a face patch were at reduced risk of the condition.

Decline in prevalence of congenital sensorineural deafness in Dalmatian dogs in the United Kingdom

Background

Congenital sensorineural deafness (CSD) is the most common type of deafness in Dalmatian dogs.

Objectives

To use results of CSD screening in Dalmatian dogs in the United Kingdom in genetic analysis and to determine any changes in the prevalence of CSD in this breed over time.

Animals

A total of 8955 Dalmatian puppies undergoing hearing function screening using brainstem auditory evoked response (BAER) between July 1992 and February 2019.

Methods

Results of BAER testing and pigmentation phenotypic data were linked to the UK Kennel Club Dalmatian pedigree database. Mixed model analysis was used to estimate variance parameters.

Results

The overall prevalence of CSD was 17.8% (13.4%, unilateral; 4.4%, bilateral). Heritability of CSD was approximately 0.3 (across models) and significantly >0. Genetic correlations between CSD and blue irises (+0.6) and pigmented head patch (−0.86) were large in magnitude and significantly different form 0. Significant improving phenotypic and genetic trends were identified, likely as the result of selection against deafness, equivalent to avoiding breeding with the 4% to 5% of animals with the highest genetic risk of CSD.

Conclusions and Clinical Importance

A decrease in the prevalence and genetic risk of CSD implies breeders have been selecting for hearing dogs. Selective breeding based on estimated breeding values (EBVs) can help further decrease the prevalence of CSD in Dalmatians in the future.

Congenital sensorineural deafness in English setters in the United Kingdom: prevalence and association with phenotype and sex

BACKGROUND

The English setter (ES) is predisposed to congenital sensorineural deafness (CSD). CSD prevalence and association with phenotype in the UK ES population are previously unreported.

METHODS

The database of the authors' institution was searched for ES puppies undergoing brainstem auditory evoked response (BAER) testing for CSD screening (2000-2018). Inclusion criteria were BAER performed at 5-10 weeks of age, testing of complete litters and available phenotypic data. The age, sex, presence of patches at birth, coat colour, iris colour, hearing status and BAER-determined parental hearing status of each puppy were recorded. Multivariable binary logistic regression was performed to determine the significance of these variables as predictors for the likelihood of puppies being unilaterally or bilaterally deaf.

RESULTS

Inclusion criteria were met for 447 puppies. Hearing was bilaterally normal in 427 (95.5 per cent) puppies. The prevalence of unilateral and bilateral CSD was 3.6 per cent and 0.9 per cent, respectively. Females were 3.3 times more likely to be deaf than males, and puppies with both parents of unknown hearing status were 4.6 times more likely to be deaf than those with at least one normal parent.

CONCLUSION

The prevalence of CSD was 4.5 per cent, with female puppies and those with two parents of unknown hearing status at greatest risk.

Prevalence of neurological disorders in French bulldog: a retrospective study of 343 cases (2002-2016)

Background

French Bulldog (FB) has significantly gained in popularity over the last few years, and seems to be frequently affected by various neurological conditions. The purpose of this retrospective study was to report the prevalences of neurological diseases in a large population of FB, presented with neurological signs between 2002 and 2016, and for which a definitive diagnosis was established. A secondary objective was to identify epidemiological characteristics regarding specific diseases in this singular breed.

Results

During the study period, 533 FBs were presented for neurological signs, representing 18.7% of all admitted FBs (N = 2846). In total, 343 FBs with definitive diagnosis were included in this descriptive epidemiological study. Hansen type I intervertebral disk herniation (IVDH) was by far the most common neurological disorder (45.5% of all cases). The IVDH location was cervical in 39.8%, and thoracolumbar in 60.2% of cases. The median ages for cervical and thoracolumbar IVDH were 4.2 and 4 years, respectively. C3-C4 was the most commonly affected disk (57.8% of cervical IDVH) all locations combined. Spinal arachnoid diverticulum (SAD) was detected in 25 FBs, representing the second most common myelopathy (11.3%). A concurrent spinal abnormality was identified in 64.0% of SAD cases. Brain tumours represented 36.8% of encephalopathies, with glioma (confirmed or suspected) being the most common. Meningoencephalitis of unknown origin (MUO) represented 25.0% of brain disorders, females less than 5.5 years being more likely to be affected. Aside from central nervous system conditions, otitis interna associated with peripheral vestibular signs and bilateral congenital deafness (associated with white coat) were also common.

Conclusions

The findings of this study suggest that FB seems to be prone to several neurological diseases. IVDH is clearly predominant in FB and cervical location seems more represented than in other breeds. FBs affected by IVDH tend to be younger than previously described, either for both cervical and thoracolumbar locations. Thoracic SAD was the second most common myelopathy, with a concurrent spinal anomaly identified in two thirds of the cases. MUO was more likely to affect young to middle-aged females. These findings could be of interest for owners, breeders, practicing veterinarians and insurance companies.

Prevalence, heritability and genetic correlations of congenital sensorineural deafness and coat pigmentation phenotype in the English bull terrier

Background

Congenital sensorineural deafness (CSD) is the most common type of deafness in dogs and it occurs in numerous canine breeds including the English bull terrier. This study estimates prevalence, heritability and genetic correlations of CSD and coat pigmentation phenotypes in the English bull terrier in England.

Results

Hearing status was assessed by brainstem auditory evoked response in 1060 English bull terrier puppies tested at 30–78 (mean 43.60) days of age as complete litters. Gender, coat and iris colour and parental hearing status were recorded.

The prevalence of CSD in all 1060 puppies was 10.19 % with 8.21 % unilaterally deaf and 1.98 % bilaterally deaf. The coat was predominately coloured in 49.15 % puppies and white with or without a patch in 50.85 % puppies. The majority (96.29 %) of deaf puppies had a white coat (with or without a patch); 19.29 % of the puppies with a white coat (with or without a patch) were deaf.

Heritability and genetic correlations were estimated using residual maximum likelihood. Heritability of hearing status as a trichotomous trait (bilaterally normal/unilaterally deaf/bilaterally deaf) was estimated at 0.15 to 0.16 and was significantly different to zero (P < 0.01). Heritability of coat pigmentation phenotype (all white/white with patches/coloured) was 0.49 (standard error 0.077). Genetic correlation of CSD with coat pigmentation phenotype was estimated at −0.36 to −0.37 (CSD associated with all white coat), but was not significantly larger than zero (P > 0.05). Analysis of CSD in all white and white patched puppies only estimated the heritability of CSD as 0.25 and was significantly greater than zero (P < 0.01), and the heritability of coat colour (all white/white with patches) as 0.20 (standard error 0.096). The genetic correlation was estimated at −0.53 to −0.54 (CSD associated with all white coat) but was just above the statistical threshold determining significant difference to zero (P = 0.06).

Conclusions

These results indicate that CSD occurs predominantly in white English bull terriers and there is genetic variation in CSD beyond that associated with coat colour.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0777-6) contains supplementary material, which is available to authorized users.

The Genetics of Deafness in Domestic Animals

Although deafness can be acquired throughout an animal's life from a variety of causes, hereditary deafness, especially congenital hereditary deafness, is a significant problem in several species. Extensive reviews exist of the genetics of deafness in humans and mice, but not for deafness in domestic animals. Hereditary deafness in many species and breeds is associated with loci for white pigmentation, where the cochlear pathology is cochleo-saccular. In other cases, there is no pigmentation association and the cochlear pathology is neuroepithelial. Late onset hereditary deafness has recently been identified in dogs and may be present but not yet recognized in other species. Few genes responsible for deafness have been identified in animals, but progress has been made for identifying genes responsible for the associated pigmentation phenotypes. Across species, the genes identified with deafness or white pigmentation patterns include MITF, PMEL, KIT, EDNRB, CDH23, TYR, and TRPM1 in dog, cat, horse, cow, pig, sheep, ferret, mink, camelid, and rabbit. Multiple causative genes are present in some species. Significant work remains in many cases to identify specific chromosomal deafness genes so that DNA testing can be used to identify carriers of the mutated genes and thereby reduce deafness prevalence.

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.

Approaches to canine health surveillance

Effective canine health surveillance systems can be used to monitor disease in the general population, prioritise disorders for strategic control and focus clinical research, and to evaluate the success of these measures. The key attributes for optimal data collection systems that support canine disease surveillance are representativeness of the general population, validity of disorder data and sustainability. Limitations in these areas present as selection bias, misclassification bias and discontinuation of the system respectively. Canine health data sources are reviewed to identify their strengths and weaknesses for supporting effective canine health surveillance. Insurance data benefit from large and well-defined denominator populations but are limited by selection bias relating to the clinical events claimed and animals covered. Veterinary referral clinical data offer good reliability for diagnoses but are limited by referral bias for the disorders and animals included. Primary-care practice data have the advantage of excellent representation of the general dog population and recording at the point of care by veterinary professionals but may encounter misclassification problems and technical difficulties related to management and analysis of large datasets. Questionnaire surveys offer speed and low cost but may suffer from low response rates, poor data validation, recall bias and ill-defined denominator population information. Canine health scheme data benefit from well-characterised disorder and animal data but reflect selection bias during the voluntary submissions process. Formal UK passive surveillance systems are limited by chronic under-reporting and selection bias. It is concluded that active collection systems using secondary health data provide the optimal resource for canine health surveillance.

Prevalence of congenital hereditary sensorineural deafness in Australian Cattle Dogs and associations with coat characteristics and sex

Background

Congenital hereditary sensorineural deafness (CHSD) occurs in many dog breeds, including Australian Cattle Dogs. In some breeds, CHSD is associated with a lack of cochlear melanocytes in the stria vascularis, certain coat characteristics, and potentially, abnormalities in neuroepithelial pigment production. This study investigates phenotypic markers for CHSD in 899 Australian Cattle Dogs.

Results

Auditory function was tested in 899 Australian Cattle Dogs in family groups using brainstem auditory evoked response testing. Coat colour and patterns, facial and body markings, gender and parental hearing status were recorded.

Deafness prevalence among all 899 dogs was 10.8% with 7.5% unilaterally deaf, and 3.3% bilaterally deaf, and amongst pups from completely tested litters (n = 696) was 11.1%, with 7.5% unilaterally deaf, and 3.6% bilaterally deaf.

Univariable and multivariable analyses revealed a negative association between deafness and bilateral facial masks (odds ratio 0.2; P ≤ 0.001). Using multivariable logistic animal modelling, the risk of deafness was lower in dogs with pigmented body spots (odds ratio 0.4; P = 0.050).

No significant associations were found between deafness and coat colour.

Within unilaterally deaf dogs with unilateral facial masks, no association was observed between the side of deafness and side of mask. The side of unilateral deafness was not significantly clustered amongst unilaterally deaf dogs from the same litter. Females were at increased risk of deafness (odds ratio from a logistic animal model 1.9; P = 0.034) after adjusting for any confounding by mask type and pigmented body spots.

Conclusions

Australian Cattle Dogs suffer from CHSD, and this disease is more common in dogs with mask-free faces, and in those without pigmented body patches. In unilaterally deaf dogs with unilateral masks, the lack of observed association between side of deafness and side of mask suggests that if CHSD is due to defects in molecular pigment pathways, the molecular control of embryonic melanoblast migration from ectoderm to skin differs from control of migration from ectoderm to cochlea. In Australian Cattle Dogs, CHSD may be more common in females.

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.