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Veterinary Clinics of North America: Small Animal Practice- Special Issue: Pediatrics - July, 1999Congenital Deafness and Its RecognitionGeorge M. Strain, PhDProfessor of Neuroscience, Veterinary Physiology, Pharmacology and Toxicology,School of Veterinary Medicine; and Associate Vice Chancellor, Office ofResearch and Graduate Studies, Louisiana State University, Baton Rouge,Louisiana, 70803This work was supported by Grant No. 1R15DC01128-01 from the NationalInstitutes of Health and by a grant from the American Kennel Club. George M. Strain, PhDComparative Biomedical SciencesSchool of Veterinary MedicineLouisiana State UniversityBaton Rouge, LA 70803(225) 578-9758(225) 578-9895 (fax)strain@lsu.eduSynopsisCongenital deafness in dogs and cats is primarily of the hereditary sensorineuralform associated with white pigmentation genes, although acquired forms ofdeafness are possible. Highest prevalence is seen in white cats, especiallythose with blue eyes, and the Dalmatian, with many other dog breeds affectedto some extent. This deafness results from degeneration of the cochlearblood supply at age 3 to 4 weeks, presumably resulting from suppressionof melanocytes by the white (cat) or merle or piebald (dog) genes. Mechanismof inheritance is not understood for most breeds. Such animals should notbe bred and may present liabilities for their owners. Objective diagnosisof deafness, especially when unilateral, relies on the brain stem auditoryevoked response, an electrodiagnostic test where electrical activity inresponse to a click stimulus is recorded from the scalp using needle electrodesand a special purpose computer. Client counseling guidelines are presented.Sensory function in neonatal dogs and cats is primarily tactile, olfactoryand gustatory. The visual and auditory senses, although partially functionalat birth, exhibit significant postnatal development: in the dog, the eyesdo not open until a puppy is 8 to 10 days of age, the ear canals do notopen until it is 12 to 13 days of age, and mature system function up throughthe cortex is not present until it is 3 months of age or older.18,22Similar delays are seen in the cat. As a result, disorders of these systemsfrequently escape early detection.Deafness can be described as (1) congenital or late onset, (2) hereditaryor acquired, and (3) conductive or sensorineural.14,15 The mostcommonly occurring deafness forms in dogs and cats are congenital hereditarysensorineural deafness, late onset acquired sensorineural deafness, andlate onset acquired conductive deafness. Distinguishing between hereditaryand acquired deafness is generally not possible without breeding trials,although an assumption of hereditary deafness can be made in breeds witha high prevalence of deafness. The most common form of deafness in youngdogs and cats is congenital hereditary sensorineural deafness, with acquiredconductive and acquired sensorineural appearing on rare occasions.PATHOPHYSIOLOGY OF DEAFNESSPerception of sound first requires transmission through the outer andmiddle ears to the cochlea for transduction by neural hair cells. Perceptionresults from (1) transmission of transduced auditory information from thecochlea by the eighth cranial nerve to the dorsal and ventral cochlear nuclei,the inferior colliculus, the medial geniculate nucleus of the thalamus,and the primary and secondary cortical auditory areas on the temporal lobe;and (2) attention to the arriving information. Commingling of ipsilateraland contralateral auditory information occurs at multiple steps in the ascentup the auditory pathway. As a result, unilateral hearing loss rarely resultsfrom lesions or disease affecting auditory structures above the eighth nerve.Central deafness (unilateral or bilateral) in the absence of severe neurologicdisease is clinically unknown in veterinary medicine and is not consideredfurther here.Conduction DeafnessConduction deafness results from blockage of sound transmission to thecochlea as a consequence of occlusion of the ear canal or middle ear cavity,or from developmental defects. Occlusion may result from excess cerumenproduction, from otitis externa or media, or from foreign objects. Developmentaldefects, which are uncommon, may include atresia of the tympanum or ossicles,fusion of the ossicles, or collapse of the ear canal from cartilaginousweakness or incomplete development. Conduction deafness may be partial orcomplete and may be reduced by intervention in some cases. Clearance bythe body of the mucopurulent discharge and detritus from otitis media mayrequire weeks to months after termination of the infection; hence, recoveryof auditory function is delayed. Hereditary forms of conduction deafnesshave not been identified in domestic species, but the appearance of sucha disorder from a spontaneous genetic defect is possible.Congenital Acquired Sensorineural DeafnessCongenital acquired sensorineural deafness, which is uncommon, can resultfrom in utero or perinatal exposure to ototoxic compounds such as maternaltreatment with aminoglycoside antibiotics,21 in utero or perinatalotitis or meningitis, anoxia, or even trauma. Breeders with animals belongingto breeds with a high prevalence of hereditary sensorineural deafness maysuggest acquired causes of deafness rather than confront the breeding andother implications of the presence of a hereditary disorder. Sensorineuraldeafness, whether hereditary or acquired, is the consequence of cochlearhair cell loss through primary or secondary mechanisms (see below).Congenital Hereditary Sensorineural DeafnessCongenital hereditary sensorineural deafness is usually seen in dog andcat breeds with white pigmentation. In the small number of canine breedswhere it is not associated with white pigmentation (Doberman and other dogbreeds not carrying piebald or merle genes),23 deafness resultsfrom the type of hair cell loss that is a primary event with unknown cause.In breeds of dogs carrying the piebald or merle genes and breeds of catscarrying the white gene, the hair cell loss is secondary to degenerationof the cochlear blood supply. Figure 1 shows a crosssection of one turn of the cochlea, demonstrating the separation of thecochlea into three parallel ducts: the scala vestibuli, the scala media(or cochlear duct), and the scala tympani which joins at the apex of thecochlea with the scala vestibuli. The outer margin of the scala media iscovered by a vascular bed, the stria vascularis. The stria is responsiblefor secretion of endocochlear fluid and maintenance of its high K+concentration which is essential to sound transduction by the sensory haircells. In pigment-associated hereditary deafness, this vascular bed degenerates,resulting in secondary loss of hair cells and deafness. The cause for thestrial degeneration is unknown, but histologic studies have demonstratedan absence of strial melanocytes, whose presence or postnatal developmentis suppressed by the piebald or merle genes. The function of melanocytesin the stria is unknown, but they appear to be critical to maintenance ofelevated K+ levels in the scala media and survival of the stria.Whether hair cell death is from primary or secondary mechanisms, the lossis permanent, as mammals are unable to regenerate cochlear neuronal tissue.In the Dalmatian, postnatal auditory function development has been shownto proceed normally up until 3 weeks of age, at which point the strial degenerationproduces rapid loss of hair cell function.6 A similar time courseis likely in other breeds of dogs and cats with pigment-associated deafness,but it has not been studied. Likewise, the time course of congenital deafnessin canine breeds not associated with white pigmentation has not been documented,but it is likely that deafness is present at birth or shortly thereafter.As a consequence of the documented 3 to 4 weeks of age at which time deafnessappears, hearing testing, as described below, is typically not performeduntil an animal reaches at least 5 weeks of age.A wide variety of breeds of dogs have been reported to have congenitaldeafness (see Table 1); not all of these cases ofdeafness have been shown to result from hereditary causes. The breeds forwhich the prevalence is known to be high are highlighted in bold, althoughsimilar high rates may occur in other breeds that do not yet routinely receivetesting. Prevalence rates measured by the author are shown in Table2 for the canine breeds most often presented for hearing testing services.The highest rates are seen in Dalmatians, of which 30% are deaf in one orboth ears; rates in other strongly affected breeds range from 8% to 20%.Typically, there are two to three unilaterally deaf animals for every bilaterallydeaf animal. In breeds with white versus non-white phenotypes (Bull Terrier,English Cocker Spaniel), there is a clear increased prevalence in the whitephenotype. Prevalence rates for pure feline breeds have not been measured,but are highest for the breeds carrying the white gene (Table3), especially in cats with blue eyes. Deafness in 256 mixed breed whitecats was reported as 12% unilateral and 38% bilateral, for a total of 50%of cats being affected (reviewed in Delack3). The prevalenceof deafness increases as the number of blue eyes increases from zero totwo, but not all blue-eyed white cats are deaf. Deafness prevalence (unilateraland bilateral) in mixed breed white cats was 17%, 40%, and 85% for zero,one, or two blue eyes, respectively.9GENETICS OF DEAFNESSPigment-associated deafness has been reported since the last century,1,5,8-10,12but the hereditary mechanisms are not yet fully understood. The merle gene,which is responsible for the pattern of dark and light hair in breeds suchas the Collie and Shetland Sheepdog, is a simple autosomal dominant gene.7Dogs that are homozygous for the merle gene are usually deaf and frequentlysolid white, blind, and sterile. Heterozygotes have an increasing tendencyto be deaf as the percent of white in the coat increases. Although the merlegeneis a dominant gene, the deafness associated with it is not inheritedas a simple dominant (or recessive) disorder.The piebald and extreme piebald genes, which are responsible for whitehair in nonmerle breeds of dogs, are simple autosomal recessive genes.7As a result, in breeds with major white areas on the body, the animals arehomozygous. An example is the Dalmatian, all of which are breed are homozygousfor the extreme piebald gene. The underlying coat color of black (dominant)or liver (recessive) is covered with white by the extreme piebald gene,and spots are produced through the white by the dominant ticking gene. Thelightness or heaviness of the spotting is thus controlled by the tickinggene and not the extreme piebald gene, and it is not a factor in the prevalenceof deafness.19 Based on studies of the Dalmatian, deafness inbreeds carrying the piebald genes is neither simple recessive nor dominant.Breeding of bilaterally hearing parents routinely produces deaf offspring;thus, the mechanism is not simple dominant. Breeding of two bilaterallydeaf parents produces both deaf and hearing offspring; the latter wouldnot occur if the defect were simple recessive and both parents were homozygous.There is no evidence for X-linked or mitochondrial hereditary mechanisms.As a consequence, inheritance of deafness associated with the piebald genesmust be polygenic or must involve incomplete expression or penetrance, orsome combination. Molecular genetic studies of deafness disorders in humansand mice suggest that this deafness may result from a defect in a gene responsiblefor regulation of the piebald genes such as one of the homeobox class ofgenes. Evidence for this comes from further findings in Dalmatians. A patchin Dalmatians is a large black or liver area present at birth when the puppyis otherwise solid white; patches are disallowed in the Dalmatian breedstandard. The patch appears to result from weak expression of the extremepiebald gene, resulting in a failure to cover the underlying coat color;patched Dalmatians are statistically less likely to be deaf than unpatchedanimals.19 When the extreme pieblad gene is strongly expressed,brown pigment is suppressed in the iris, resulting in blue eyes (and frequentlyan absence of pigment in the tapetum lucidum), and melanocytes are suppressedin the cochlear stria vascularis, resulting in deafness. Blue-eyed Dalmatiansare statistically more likely to be deaf than brown-eyed animals.19The blue eye is permitted in the breed standard in the United States butnot in Canada, Mexico, or Europe. The prevalence of deafness is lower inEurope (combined unilateral and bilateral deafness is 21% in the UnitedKingdom and 18% in Holland compared to 30% in the United States), and breedingaway from blue eyes was shown to reduce deafness in Norway.4It is not known if differences exist for deafness associated with the twodifferent piebald genes.Deafness in the Doberman Pinscher, which is accompanied by transientvestibular dysfunction, is transmitted by a simple recessive mechanism.23Pigment-associated congenital hereditary sensorineural deafness in thecat is linked to the white gene, which is dominant over color and is unrelatedto albinism.13 On occasion these cats will have a head spot andusually have one or two blue eyes. Although the white gene is dominant,not all carriers are deaf; thus, deafness is not simply inherited.BEHAVIORAL INDICATORS OF DEAFNESSNewborn puppies and kittens with undeveloped auditory and visual functionuse other sensory cues for their feeding, elimination, and locomotion behaviors.As auditory development proceeds, they can detect loud noises, despite theunopened ear canal. Breeders relying on this for home testing may find themselvesto have been in error at a later date. Behavioral testing of hearing afteropening of the canal relies on detection of a response to sound stimuliin the absence of other detectable sensory signals. These noises shouldbe produced outside of the visual fields, avoiding visual cues, vibratorycues, touch, and air movements. Behavioral testing has limited value; animalresponses rapidly adapt even when hearing is present, stressed animals withintact hearing may fail to respond, and unilateral deafness cannot be detected.In unilaterally deaf animals, the only behavioral sign of deafness is adifficulty in localizing the source of a sound, and many animals adapt tothat also. Behavioral deafness detection with young animals in the homeis difficult, as the deaf young cue off the behavior of their littermates.A puppy or kitten that does not awaken in response to a loud noise is almostcertainly bilaterally deaf, but the unilaterally deaf cannot be detectedwith any reliability. As a consequence, behavioral hearing assessment ofanimals in the clinic or home is of limited reliability, and electrodiagnostictests are used for objective assessment.ELECTRODIAGNOSIS OF DEAFNESSThe most widely used electrodiagnostic test of hearing is the brain stemauditory evoked response (BAER), also known as the brain stem auditory evokedpotential (BAEP) or the auditory brain stem response (ABR). This test wasfirst used in veterinary research applications in the 1970s, and in clinicalveterinary applications in the early 1980s. The BAER detects electricalactivity in the cochlea and auditory pathways in the brain in much the sameway that an electrocardiogram detects electrical activity in the heart.17The response waveform consists of a series of peaks labeled with Roman numerals:peak I is produced by the cochlea and auditory nerve, and later peaks areproduced within the brain. The response from an ear that is deaf is an essentiallyflat line. In the sample recordings in Figure 2,the Dalmatian puppy in tracing A could hear in the tested ear, althoughthe Dalmatian puppy in tracing B was deaf in the tested ear, with an essentiallyflat response. Because the response amplitude is quite small, it is necessaryto average the responses to multiple stimuli (clicks) to unmask them fromthe other unrelated electrical activity that is also present on the scalp(e.g., electroencephalographic activity, muscle activity).The response is collected with a special computer through small subdermalneedle electrodes: one is placed in front of each ear, one is placed atthe top of the head, and a ground electrode is placed either between andbehind the eyes or on the neck. It is rare for a dog to show any evidenceof pain from the placement of the electrodes - if anything the dog objectsto the gentle restraint and the presence of wires hanging in front of itsface. A stimulus click (air-conducted) produced by the computer is directedinto the ear with a foam insert earphone. Each ear is tested individually,and the test usually is complete in 10 to15 minutes. Sedation or anesthesiais unnecessary unless the dog becomes extremely agitated, which can usuallybe avoided with patient and gentle handling. Sedation or anesthesia doesnot materially affect the BAER.The click stimulus used contains most of the audible frequencies of thedog and cat, with the exception of the very highest perceived frequencies.Accordingly, the BAER is a frequency nonspecific test that is more usefulfor detecting the presence or total absence of auditory function withoutquantifying hearing loss in decibels. Assessment of the normalcy of a responseis based on identification of the presence of Peak I within a narrow expectedtime frame (which varies based on the equipment used) and the presence ofthe expected pattern of peaks. With progressive hearing loss, there is areduction in the amplitude of the BAER peaks and an increase in peak latencies;thus, a subjective assessment of partial hearing loss can be made but notquantified, and differing degrees of loss in different frequency rangescannot be determined. Diagnosis of partial hearing loss based on the BAERis done only with great caution, as a number of technical factors can affectpeak amplitude and latency in subjects with normal hearing.17Fortunately, partial hearing loss is rare in puppies or kittens.The BAER demonstrates maturational changes.22 Because thegreater portion of the BAER originates in the brain stem, there is lesspostnatal development than is seen in tests of other sensory modalities;however, postnatal development is greater in altricial species like thedog and cat than in precocial species like the horse and cow. Full maturationof the BAER occurs by 40 days in the dog and the cat. The BAER can be recordedin response to loud stimuli prior to the opening of the ear canal, but thisis not of use as it predates the age at which deafness is manifested.In some circumstances, it is useful to be able to differentiate betweensensorineural and conductive deafness, as this can affect breeding decisionsand whether a young animal is placed in a show home or a pet home. Whena BAER indicates deafness in an animal in which conduction deafness mightbe suspected (i.e., long-eared breed, recent ear infection), the test isrepeated with a mechanical transducer that transmits the stimulus clickas a vibration through bone rather than through air conduction.20Because the cochlea is imbedded in bone, the bone-conducted BAER bypassesthe outer and middle ears, the sites of conduction blockade, and directlyactivates the cochlea. The response appearance is the same as an air-conductedBAER, but the peaks occur at a shorter latency due to the shorter path traversedby the stimulus (Figure 2).A limited availability of BAER testing sites blocks some potential usersfrom access, but the number of test locations is increasing beyond the originalveterinary school sites. The equipment cost of approximately $20,000 andan absence of formal veterinary training programs outside of neurology residencieshave impeded ready access. A listing of available national and internationalsites is maintained at the author's Web site,16 which is alsoa resource of additional information on deafness.CLIENT COUNSELING ISSUESAdvice to clients faced with a deaf puppy or kitten varries based onbreed, animal age, home environment, unilateral versus bilateral deafness,and other factors. Bilaterally deaf animals present a variety of liabilitiesand emotional land mines, more so for dogs than for cats. Deaf animals areat risk of injury or death from undetected dangers such as motor vehicles.When startled, they may reflexly bite, which is a special concern aroundinfants and toddlers. Anxious or aggressive personalities may develop indeaf dogs from constantly being subjected to startle, and familiar familymembers and friends may be attacked without warning or cause. Not all deafdogs develop these problems, and no data exist on prevalence rates for suchevents, but there is no way to predict which animals may or may not havethese experiences. Based on inherent temperament differences, there mayalso be variation between breeds in the likelihood of such problems. Bilaterallydeaf dogs are very difficult to raise and train; as a result, they oftenend up in animal control shelters. From there, they may be reclaimed bybreed rescue groups, after which the cycle may begin again. House cats presentfewer problems, but outdoor cats may fall victim to motor vehicles. An emotionalcost is invariably paid by the owners of those animals that cannot copeor adjust to their disability, both from the perspective of management andthat of facing the decision as to whether to euthanize an animal with whichan emotional attachment has formed. Unilateral deafness does not pose suchproblems.Because of the many problems associated with bilaterally deaf dogs andthe surplus of available puppies, the Dalmatian Club of America has an officialposition calling for the euthanasia of deaf puppies, with the emphasis onbreeders rather than new owners. Similar sentiment is held by the officialorganizations of other breeds with high deafness prevalence rates, but thesegroups have not adopted such an official policy. This position has generatedconsiderable controversy within the purebred dog community, the generaldog-owning community, the veterinary community, and the human deaf community,but it is probably appropriate when divorced from emotional considerations.Resources exist for those owners opting to keep a deaf dog. Books havebeen written on living with a deaf dog,2 including directionsfor training deaf dogs to respond to American Sign Language signs, and webpages have been posted with information and support content. Deaf dogs andcats learn to respond to flashing porch lights and vibrating collars,16and can cue off the behavior of other animals in the household. In suchcircumstances, the owner should be instructed in protecting the animal fromthe inherent dangers associated with deafness: both dangers to the deafanimal and dangers to people around the deaf animal.Genetic counseling for owners of deaf dogs and cats cannot be presentedwith total assurance because of the incomplete knowledge of mechanisms ofdeafness inheritance. It can be stated that deaf animals in breeds witha high known prevalence of either unilateral or bilateral deafness shouldnot be bred; unilaterally deaf animals have the genetic defect but haveone ear spared. Over the long run, such breedings have the probability ofproducing more deaf animals. In addition, it may not be advisable to breedto animals from litters which had a high percentage of deaf animals or fromlines with a history of producing high percentages of deaf animals. Themost conservative approach avoids any possible introduction of defectivegenes, but may be difficult in certain breeds. A deaf animal from one ofthese breeds must be assumed to have hereditary deafness instead of acquireddeafness unless the clinical history convincingly indicates otherwise. Becauseof the association between deafness and blue eyes in the Dalmatian, it isalso advisable to not breed blue-eyed dogs from those breeds in which theblue eye is not a standard part of the breed phenotype.If a deaf animal is presented from a breed with no history of notablenumbers of deaf animals, the guidelines for advice are murkier. The mostconservative approach is not to breed any affected animal, especially ifthe breed is one carrying piebald or merle genes, unless the clinical historysuggests a likely acquired cause such as otitis or drug ototoxicity. Eventhese latter cases are not without risk unless precedent documentation ofnormal hearing exists.In an effort to promote research to reduce deafness and provide datafor potential breeders, several national breed organizations in this countryhave set up hearing registries either managed by the breed organization(e.g., English Setter Association of America) or by a contracted secondparty (e.g., Dalmatian Club of America managed by the Institute for GeneticDisease Control in Animals, Bull Terrier Club of America managed by theOrthopedic Foundation of America). The first registry is closed, althoughthe second is open and the third offers the option of being either closedor open to qualified members of the public. Current canine deafness researchfocuses on determining mechanisms of inheritance from extended pedigreesand on identifying the responsible defective genes using molecular biologicaltechniques.References1. Anderson H, Henricson B, Lundquist P-G, et al: Genetic hearing impairmentin the Dalmatian dog. Acta Oto-Laryngol Suppl 23:1, 19682. Becker, SC: Living With a Deaf Dog. Cincinnati, Susan Cope Becker,19983. Delack JB: Hereditary deafness in the white cat. Compend Cont Ed PractVet 6:609, 19844. Greibrokk T: Hereditary deafness in the Dalmatian: Relationship toeye and coat color. J Amer Anim Hosp Assn 30:170, 19945. Hudson WR, Ruben RJ: Hereditary deafness in the Dalmatian dog. ArchOtolaryngol 75:213, 19626. Johnsson LG, Hawkins JE Jr, Muraski AA, et al: Vascular anatomy andpathology of the cochlea in Dalmatian dogs. In: de Lorenzo, AJD(ed): Vascular Disorders and Hearing Defects. Baltimore: University ParkPress, 1973, p 2497. Little CC: The Inheritance of Coat Color In Dogs. New York: Howell,19578. Lurie MH: The membranous labyrinth in the congenitally deaf collieand Dalmatian dog. Laryngoscope 58:279, 19489. Mair IWS: Hereditary deafness in the white cat. Acta Otolaryngol Suppl314:1, 197310. Mair IWS: Hereditary deafness in the Dalmatian dog. Arch Otorhinolaryngol212:1, 197611. Pujol R, Hilding D: Anatomy and physiology of the onset of auditoryfunction. Acta Otolaryngol 76:1, 197312. Rawitz B: Gehörorgan und Gehirn eines Weissen Hundes mit blauenAugen. Morphol Arbeiten 6:545, 189613. Searle AG: Comparative Genetics of Coat Color in Mammals. London:Logos Press, 196814. Strain GM: Congenital deafness in dogs and cats. Compend Cont EdPract Vet 13:245, 1991.15. Strain GM: Aetiology, prevalence, and diagnosis of deafness in dogsand cats. Brit Vet J 152:17, 199616. Strain GM: Deafness in dogs and cats. Located at: http://www.lsu.edu/deafness/deaf.htm17. Strain GM: Electrophysiological assessment of auditory function.Proc. 15th ACVIM Forum 15:617. 1997.18. Strain GM, Jackson RM, Tedford BL: Postnatal development of the visual-evokedpotential in dogs. Am J Vet Res 52:231, 199119. Strain GM, Kearney MT, Gignac IJ, et al: Brainstem auditory evokedpotential assessment of congenital deafness in Dalmatians: associationswith phenotypic markers. J Vet Internal Med 6:175, 199220. Strain GM, Green KD, Twedt AC, et al: Brain stem auditory evokedpotentials from bone stimulation in dogs. Am J Vet Res 54:1817, 199321. Strain GM, Tedford L, Jackson RM: Postnatal development of the brainstemauditory-evoked potential in dogs. Am J Vet Res 52:410, 199422. Strain GM, Merchant SR, Neer TM, et al: Ototoxicity assessment ofa gentamicin sulfate otic preparation in dogs. Am J Vet Res 56:532, 199523. Wilkes MK, Palmer AC: Congenital deafness and vestibular deficitin the doberman. J Small Anim Pract 33:218, 1992Table 1. Breeds With Reported Congenital DeafnessAkitaDoberman PinscherPapillonAmerican-Canadian ShepherdDogo ArgentinoPit Bull TerrierAmerican EskimoEnglish BulldogPointerAmerican Staffordshire TerrierEnglish Cocker SpanielPuliAustralian Cattle DogEnglish SetterRhodesian RidgebackAustralian ShepherdFoxhoundRottweilerBeagleFox TerrierSaint BernardBichon FriseFrench BulldogSchnauzerBorder CollieGerman ShepherdScottish TerrierBorzoiGreat DaneSealyham TerrierBoston TerrierGreat PyreneesShetland SheepdogBoxerIbizan HoundShropshire TerrierBulldogItalian GreyhoundSiberian HuskyBull TerrierJack Russell TerrierSoft Coated Wheaten TerrierCardigan Welsh CorgiKuvaszSpringer SpanielCatahoula Leopard DogLabrador RetrieverSussex SpanielCavalier King Charles SpanielMalteseTibetan SpanielChihuahuaMiniature PinscherTibetan TerrierChow ChowMiniature PoodleToy PoodleCocker SpanielmongrelWalker American FoxhoundCollieNorwegian DunkerhoundWest Highland White TerrierDalmatianNova Scotia Duck Tolling RetrieverWhippetDappled DachshundOld English SheepdogYorkshire Terrier (n=69)Table 2. Dog Breed-Specific Deafness Prevalence(percent)BreedDogsTestedBilaterally HearingUnilaterallyDeafBilaterallyDeafTotalDeafDalmatian500970.2% (3510)22.0% (1100)8.0% (399)30.0% (1499)Bull Terrier57389.0% (510)9.9% (57)1.0% (6)11.0% (63)white29980.9% (242)17.1% (51)2.0% (6)19.1% (57)colored27297.8% (266)2.2% (6)0.0% (0)2.2% (6)English Setter53085.7% (454)12.1% (64)2.3% (12)14.3% (76)English Cocker Spaniel82892.8% (768)6.2% (51)1.1% (9)7.2% (60)parti color79492.6% (735)6.3% (50)1.1% (9)7.4% (59)solid color3497.1% (33)2.9% (1)0.0% (0)2.9% (1)Australian Cattle Dog23887.4% (208)10.5% (25)2.1% (5)12.6% (30)Catahoula Leopard Dog4831.3% (15)27.1% (13)41.7% (20)68.8% (33)Jack Russell Terrier4780.9% (38)8.5% (4)10.6% (5)19.1% (9)November 15, 1998Table 3. Cat Breeds Carrying the White (W)Coat Pigment GeneWhiteWhite Scottish FoldEuropean WhiteWhite Turkish AngoraForeign WhiteWhite American WirehairWhite Cornish RexWhite American ShorthairWhite Devon RexWhite British ShorthairWhite ManxWhite Exotic ShorthairWhite PersianWhite Oriental Shorthair Figure 1. Cross-section of the cochlea. The organ of Corti rests on thebasilar membrane, with its hair cell cilia embedded in the tectorial membrane.The stria vascularis on the outer margin of the scala media secretes theendocochlear fluid of the scala media and maintains a high K+concentration essential to sound transduction by the hair cells. Sensorineuraldeafness can result from primary or secondary loss of cochlear hair cells.(From Bloom W, Fawcett DW: A Textbook of Histology, ed 10. Philadelphia:WB Saunders, 1975; with permission.)  Figure 2. Brain stem auditory evoked responses (BAER) recorded from puppies;cat BAER appear similar. A. A BAER from a normal dog in responseto an air-conducted click stimulus. Peak I in the response is generatedby the cochlea and VIIIth cranial nerve, while later peaks are generatedin brain stem structures. B. A BAER from a dea0f Dalmatian. C.A BAER from a normal dog in response to a bone-conducted click stimulus. |
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