Hereditary Deafness in Dogs and Cats

Slide 1:Hereditary Deafness in Dogs and Cats

George M. Strain Louisiana State University Baton Rouge, Louisiana USA Causes, Prevalence, and Current Research

Slide 2:Outline

anatomy and physiology forms of deafness hearing testing pigment genes and hereditary deafness prevalence and breeds genetics of deafness current research

Slide 3:Ear Anatomy:

outer ear middle ear inner ear

Slide 6:In this cross section through one coil of the cochlea, the receptor nerve cells (hair cells) are located in the middle compartment (the scala media). Vibrations transmitted in the two outer compartments cause bending of the hair cell cilia, initiating nerve impulses. The special makeup of the fluid of the middle compartment is produced by the stria vascularis on the outside border. This tissue degenerates at 3 weeks of age. The other tissues then degenerate and collapse in on themselves.In this cross section through one coil of the cochlea, the receptor nerve cells (hair cells) are located in the middle compartment (the scala media). Vibrations transmitted in the two outer compartments cause bending of the hair cell cilia, initiating nerve impulses. The special makeup of the fluid of the middle compartment is produced by the stria vascularis on the outside border. This tissue degenerates at 3 weeks of age. The other tissues then degenerate and collapse in on themselves.

Slide 8:Approximate Hearing Ranges (Hz)

human 64-23,000 sheep 100-30,000 dog 67-45,000 rabbit 360-42,000 cat 45-64,000 rat 200-76,000 cow 23-35,000 mouse 1,000-91,000 horse 55-33,500 porpoise 75-150,000 (See www.lsu.edu/deafness/HearingRange.html for more species)

Slide 9:Forms of Deafness

inherited or acquired congenital or later-onset sensorineural or conductive result: eight possible combinations (i.e., acquired later-onset sensorineural deafness) There are many ways to look at deafness - this one seems to be helpful. Deafness can be classified by these three sets of descriptors. By combining them, 8 possible combinations result. The three forms most common in dogs are: 1. inherited, congenital, sensorineural 2. acquired, later-onset, sensorineural 3. acquired, later-onset, conductive I have not seen any inherited deafness that is later-onset, and I have not seen any inherited conductive deafness.There are many ways to look at deafness - this one seems to be helpful. Deafness can be classified by these three sets of descriptors. By combining them, 8 possible combinations result. The three forms most common in dogs are: 1. inherited, congenital, sensorineural 2. acquired, later-onset, sensorineural 3. acquired, later-onset, conductive I have not seen any inherited deafness that is later-onset, and I have not seen any inherited conductive deafness.

Slide 10:sensorineural (nerve) deafness - loss of auditory function because of loss of cochlear hair cells or the cochlear nerve neurons they connect to conductive deafness - blockage of sound transmission through outer and/or middle ear without damage to cochlea

Definitions Sensorineural deafness can result from direct damage to the hair cells, or indirectly from damage to the blood supply. Sensorineural deafness is not reversible in mammals. Conductive deafness may resolve or may be treatable in some cases.Sensorineural deafness can result from direct damage to the hair cells, or indirectly from damage to the blood supply. Sensorineural deafness is not reversible in mammals. Conductive deafness may resolve or may be treatable in some cases.

Slide 11:Most Common Forms of Deafness

hereditary congenital sensorineural acquired later-onset sensorineural acquired later-onset conductive (with human deafness, the terms syndromic and nonsyndromic deafness are also used to distinguish deafness accompanied by other health problems, such as Alport syndrome) There are many ways to look at deafness - this one seems to be helpful. Deafness can be classified by these three sets of descriptors. By combining them, 8 possible combinations result. The three forms most common in dogs are: 1. inherited, congenital, sensorineural 2. acquired, later-onset, sensorineural 3. acquired, later-onset, conductive I have not seen any inherited deafness that is later-onset, and I have not seen any inherited conductive deafness.There are many ways to look at deafness - this one seems to be helpful. Deafness can be classified by these three sets of descriptors. By combining them, 8 possible combinations result. The three forms most common in dogs are: 1. inherited, congenital, sensorineural 2. acquired, later-onset, sensorineural 3. acquired, later-onset, conductive I have not seen any inherited deafness that is later-onset, and I have not seen any inherited conductive deafness.

Slide 12:Conductive deafness usually results from: 1) chronic otitis externa, where the canal tissues hypertrophy and a stenosis forms. 2) excess cerumen (ear wax) production. 3) pus residue after otitis media, which may take weeks or months for the body to clear up. These are less common in Dalmatians than some other breeds, and are not hereditary.Conductive deafness usually results from: 1) chronic otitis externa, where the canal tissues hypertrophy and a stenosis forms. 2) excess cerumen (ear wax) production. 3) pus residue after otitis media, which may take weeks or months for the body to clear up. These are less common in Dalmatians than some other breeds, and are not hereditary.

Slide 13:Hearing Testing

behavioral testing - sound stimuli produced outside of the animal's visual field cannot detect unilateral deafness animals quickly adapt to testing stimuli detected through other sensory modalities electrodiagnostic testing - brainstem auditory evoked response (BAER, BAEP, ABR) objective, non-invasive detects unilateral deafness limited availability It might be useful to review how hearing testing is performed. Behavioral testing is not very reliable and does not detect unilaterally deaf dogs. Electrodiagnostic testing is objective and reliable, but not yet widely available.It might be useful to review how hearing testing is performed. Behavioral testing is not very reliable and does not detect unilaterally deaf dogs. Electrodiagnostic testing is objective and reliable, but not yet widely available.

Slide 14:This is my electrodiagnostic testing machine - a Cadwell Sierra (brand) portable. Scalp electrodes are placed on the head and an auditory stimulus, a click, is transmitted to the ear. The computer records the responses through the electrodes, and averages many responses together to unmask the response which is hidden by muscle activity and EEG.This is my electrodiagnostic testing machine - a Cadwell Sierra (brand) portable. Scalp electrodes are placed on the head and an auditory stimulus, a click, is transmitted to the ear. The computer records the responses through the electrodes, and averages many responses together to unmask the response which is hidden by muscle activity and EEG.

Slide 15:Some testers use headphones, but they are difficult to hold on the head and may actually compress the ear canal, producing a false conduction deafness. Insert earphones are held just outside the opening of the ear canal.Some testers use headphones, but they are difficult to hold on the head and may actually compress the ear canal, producing a false conduction deafness. Insert earphones are held just outside the opening of the ear canal.

Slide 16:This shows the placement of the scalp electrodes and the positioning of the insert earphone. The computer records the electrical activity between the vertex (top) and the stimulated ear. A ground wire is between the eyes. Anesthesia or sedation are not required for testing. I have only sedated one dog in the ~7,000 dogs I have tested.This shows the placement of the scalp electrodes and the positioning of the insert earphone. The computer records the electrical activity between the vertex (top) and the stimulated ear. A ground wire is between the eyes. Anesthesia or sedation are not required for testing. I have only sedated one dog in the ~7,000 dogs I have tested.

Slide 17:Brainstem Auditory Evoked Response

hearing uni uni deaf This shows BAER responses for 4 Dal puppies. Peak I is produced by the cochlea and auditory nerve. The other peaks are produced in the brain. If the cochlea is destroyed the first peak cannot be produced, so the later peaks cannot be produced either. Puppy 1 was normal. Puppies 2 and 3 were uni's. Puppy 4 was bilaterally deaf.This shows BAER responses for 4 Dal puppies. Peak I is produced by the cochlea and auditory nerve. The other peaks are produced in the brain. If the cochlea is destroyed the first peak cannot be produced, so the later peaks cannot be produced either. Puppy 1 was normal. Puppies 2 and 3 were uni's. Puppy 4 was bilaterally deaf.

Slide 19:Hereditary CongenitalSensorineural Deafness

usually linked to the genes responsible for white Dog � recessive alleles of the piebald gene: Irish spotting (si), piebald (sp), extreme-white piebald (sw) Dog - merle (M) gene Cat - white (W) gene Cat - piebald (s) gene (?) deafness develops at 3-4 weeks of age when the blood supply to the cochlea (stria vascularis) degenerates degeneration is thought to result from an absence of pigment cells (melanocytes) which normally help maintain the ionic concentrations of K+ and Na+ other pigmentation effects are frequently seen We will focus today on inherited congenital sensorineural deafness. Dalmatians have the extreme piebald gene. In studies in my laboratory we have followed the development of hearing in Dal puppies, and found that they go deaf at 3-4 weeks of age. The function of melanocytes in the stria is not known. Similar pigment-associated hearing defects are seen in other species also (mouse, cat, etc.)We will focus today on inherited congenital sensorineural deafness. Dalmatians have the extreme piebald gene. In studies in my laboratory we have followed the development of hearing in Dal puppies, and found that they go deaf at 3-4 weeks of age. The function of melanocytes in the stria is not known. Similar pigment-associated hearing defects are seen in other species also (mouse, cat, etc.)

Slide 20:This dog (Demi Azure) demonstrates some of the common pigment changes seen in Dals. Half of the left iris is blue because the piebald gene suppressed pigmentation there, and pigment is missing from the back of the retina - this shows up as red from the blood vessels that are no longer covered by pigmentation. I will present this dog's pedigree later.This dog (Demi Azure) demonstrates some of the common pigment changes seen in Dals. Half of the left iris is blue because the piebald gene suppressed pigmentation there, and pigment is missing from the back of the retina - this shows up as red from the blood vessels that are no longer covered by pigmentation. I will present this dog's pedigree later.

Slide 24:Dog Breeds With Congenital Deafness

reported in over 80 dog breeds prevalence (unilateral & bilateral) highest in: Dalmatian (n=5,333) 30% white bull terrier (n=346) 20% English setter (n=3,656) 8% English cocker spaniel (n=1,136) 7% Australian cattle dog (n=296) 15% Jack Russell terrier (n=56) 16%* Catahoula leopard dog (n=78) 63%* (prevalence unknown for most breeds) Congenital deafness (not necessarily hereditary) has been seen in over 60 breeds. This data is from the US only. The percentages include both unilateral and bilateral deafness. All of these breeds have the piebald gene. Other breeds with the piebald gene may have a similar problem, but are not routinely seeking hearing testing services.Congenital deafness (not necessarily hereditary) has been seen in over 60 breeds. This data is from the US only. The percentages include both unilateral and bilateral deafness. All of these breeds have the piebald gene. Other breeds with the piebald gene may have a similar problem, but are not routinely seeking hearing testing services.

Slide 25:Prevalence in White Cats � Non-Pure Breed

From 2 studies: deafness (unilateral and bilateral) in purpose-bred white kittens was 52% or 43%, respectively (n=66, 162) WW: 96% & 52% Ww: 24% & 27% Deafness was 3-5 times more likely in cats with 2 blue eyes than cats with none, and 2 times more common in cats with only 1 blue eye Congenital deafness (not necessarily hereditary) has been seen in over 60 breeds. This data is from the US only. The percentages include both unilateral and bilateral deafness. All of these breeds have the piebald gene. Other breeds with the piebald gene may have a similar problem, but are not routinely seeking hearing testing services.Congenital deafness (not necessarily hereditary) has been seen in over 60 breeds. This data is from the US only. The percentages include both unilateral and bilateral deafness. All of these breeds have the piebald gene. Other breeds with the piebald gene may have a similar problem, but are not routinely seeking hearing testing services.

Slide 26:Cat Breeds With the Dominant White Gene (W)

White Cornish Rex White Devon Rex White British Shorthair White Manx White Exotic Shorthair White Persian White Oriental Shorthair White White Scottish Fold European White White Turkish Angora Foreign White White American Wirehair White American Shorthair (List may be incomplete or duplicative � please correct me if so!) Congenital deafness (not necessarily hereditary) has been seen in over 60 breeds. This data is from the US only. The percentages include both unilateral and bilateral deafness. All of these breeds have the piebald gene. Other breeds with the piebald gene may have a similar problem, but are not routinely seeking hearing testing services.Congenital deafness (not necessarily hereditary) has been seen in over 60 breeds. This data is from the US only. The percentages include both unilateral and bilateral deafness. All of these breeds have the piebald gene. Other breeds with the piebald gene may have a similar problem, but are not routinely seeking hearing testing services.

Slide 27:Genetics of Congenital Deafness - Dog

Doberman deafness � simple autosomal recessive, vestibular dysfunction, not pigment-associated �nervous� pointer deafness � simple autosomal recessive (bred for anxiety research studies) pigment-associated deafness in dogs - ? merle gene (M) - dominant; homozygous dogs may have additional health problems piebald gene (p) - recessive, but all white-carrying dogs in the breed are homozygous � deafness probably due to a single �locus� with modifier genes � NOT simple autosomal recessive The inheritance of deafness is not understood in most breeds. For the Doberman it hasbeen shown to be simple recessive. For Dal it appears that more than one gene is involved. Incomplete penetrance may also be involved - in this situation, an animal inherits a syndrome but does not show all aspects of it. So, a dog may "inherit deafness" but not actually go deaf. This is what probably happens with the good ear in unilateral deafness.The inheritance of deafness is not understood in most breeds. For the Doberman it hasbeen shown to be simple recessive. For Dal it appears that more than one gene is involved. Incomplete penetrance may also be involved - in this situation, an animal inherits a syndrome but does not show all aspects of it. So, a dog may "inherit deafness" but not actually go deaf. This is what probably happens with the good ear in unilateral deafness.

Slide 28:Demi Azure Pedigree

To show the complexity of deafness inheritance in Dals, this is the pedigree of Demi Azure. Born from two accidentally bred uni parents, she was one of only two affected in a litter of 8. She was bred in my laboratory to a deaf male (Bubba) twice. The first litter had 1 deaf from 5 survivors. The second litter had 8 deaf from 11 survivors. This does not resemble simple recessive or dominant inheritance. If it was simple recessive, all should have been deaf. If deafness is simple dominant, half of all Dalmatians should be deaf.To show the complexity of deafness inheritance in Dals, this is the pedigree of Demi Azure. Born from two accidentally bred uni parents, she was one of only two affected in a litter of 8. She was bred in my laboratory to a deaf male (Bubba) twice. The first litter had 1 deaf from 5 survivors. The second litter had 8 deaf from 11 survivors. This does not resemble simple recessive or dominant inheritance. If it was simple recessive, all should have been deaf. If deafness is simple dominant, half of all Dalmatians should be deaf.

Slide 29:Genetics of Congenital Deafness - Cat

domestic white cats have been studied the most � absence of studies of pure breeds as in white gene-carrying dogs, inheritance does not follow inheritance of the gene itself in white cats: white gene (W) - dominant; homozygous cats do not appear to have additional health problems, except possibly reduced fetal survival piebald gene (s) - recessive, uncertain that gene truly exists in cats The inheritance of deafness is not understood in most breeds. For the Doberman it hasbeen shown to be simple recessive. For Dal it appears that more than one gene is involved. Incomplete penetrance may also be involved - in this situation, an animal inherits a syndrome but does not show all aspects of it. So, a dog may "inherit deafness" but not actually go deaf. This is what probably happens with the good ear in unilateral deafness.The inheritance of deafness is not understood in most breeds. For the Doberman it hasbeen shown to be simple recessive. For Dal it appears that more than one gene is involved. Incomplete penetrance may also be involved - in this situation, an animal inherits a syndrome but does not show all aspects of it. So, a dog may "inherit deafness" but not actually go deaf. This is what probably happens with the good ear in unilateral deafness.

Slide 30:Observations on Features of Pigment-Associated Congenital Hereditary Sensorineural Deafness Based on Studies in the Dalmatian

Slide 31:Dalmatian Deafness Prevalence in the US

N=5,333 70.1% (3,740) 21.9% (1,167) 8.0% (426) This graph shows the prevalence of deafness in Dalmatians in the US that I have tested - 4,871 animals. 70.1% heard in both ears. 21.9% were deaf in one ear. 8.0% were deaf in both ears. So, 29.9% of US Dals were deaf in one or both ears. This graph shows the prevalence of deafness in Dalmatians in the US that I have tested - 4,871 animals. 70.1% heard in both ears. 21.9% were deaf in one ear. 8.0% were deaf in both ears. So, 29.9% of US Dals were deaf in one or both ears.

Slide 32:Effect of Parent Hearing Status On Deafness Prevalence

B-B Parents (N=2,320) B-U Parents (N=728) 73% 21% 6% 59% 31% 11% If deafness is hereditary in the Dalmatian, puppies bred from parents who both hear in both ears (B-B) should have a lower prevalence of deafness than those where one parent was unilaterally deaf (B-U). That was true, providing support for a hereditary component to Dalmatian deafness. This does not mean, however, that other factors do not play a role.If deafness is hereditary in the Dalmatian, puppies bred from parents who both hear in both ears (B-B) should have a lower prevalence of deafness than those where one parent was unilaterally deaf (B-U). That was true, providing support for a hereditary component to Dalmatian deafness. This does not mean, however, that other factors do not play a role.

Slide 33:Effect of Sex On Deafness Prevalence

Male (N=2,459) 71% 22% 7% 69% 22% 9% Female (N=2,424) There is considerable controversy on whether one sex is more likely to be deaf than another. Studies in England, Norway, the Netherlands, and one study in the US found more deafness in females; this difference was statistically significant in two studies. I found no statistical difference between males and females in my studies. I do not know why we get different results.There is considerable controversy on whether one sex is more likely to be deaf than another. Studies in England, Norway, the Netherlands, and one study in the US found more deafness in females; this difference was statistically significant in two studies. I found no statistical difference between males and females in my studies. I do not know why we get different results.

Slide 34:Coat Pigmentation Genes In Dalmatians

base coat - underlying coat color B - black (dominant) b - liver (recessive) extreme-white piebald gene - sw - white covering; recessive but homozygous in all Dalmatians [hair is white if it contains no pigment granules (melanin) or other substances which absorb light] ticking gene - T - dominant, produces holes in white to show underlying coat color Is pigmentation a factor in deafness? Three pigment genes determine the appearance of Dalmatians. Normal white hair (with the piebald gene) results from an absence of pigment granules because melanocytes are missing. It is not the same as albinism, where melanocytes are present but there is a total absence of pigment resulting from absence of the enzyme needed to make melanin. The extreme piebald gene appears to be the one associated with deafness, based on studies in many species.Is pigmentation a factor in deafness? Three pigment genes determine the appearance of Dalmatians. Normal white hair (with the piebald gene) results from an absence of pigment granules because melanocytes are missing. It is not the same as albinism, where melanocytes are present but there is a total absence of pigment resulting from absence of the enzyme needed to make melanin. The extreme piebald gene appears to be the one associated with deafness, based on studies in many species.

Slide 35:Effect of Varying the Expression of the Extreme-White Piebald Gene

weak gene expression: failure of the piebald gene to completely suppress the underlying coat color (black or liver); results in a patch, animals are less likely to be deaf strong gene expression: suppresses pigmentation in the iris (blue eyes) and tapetum (red eye), and in the stria vascularis (deafness) It appears that several factors or genes influence how strongly the extreme piebald gene is expressed in the Dalmatian. When it is weakly expressed patches result. When it is strongly expressed blue eyes result and deafness may occur. Not all blue-eyed dogs are deaf. but there is a strong relationship.It appears that several factors or genes influence how strongly the extreme piebald gene is expressed in the Dalmatian. When it is weakly expressed patches result. When it is strongly expressed blue eyes result and deafness may occur. Not all blue-eyed dogs are deaf. but there is a strong relationship.

Slide 36:Effect of Patch On Deafness Prevalence

Patched (N=436) Not Patched (N=4,404) 90% 8% 2% 68% 23% 9% This appears to be born out by the results shown in this graph. Dals with a patch had much less deafness than Dals without a patch.This appears to be born out by the results shown in this graph. Dals with a patch had much less deafness than Dals without a patch.

Slide 37:Effect of Eye Color (Brown or Blue) On Deafness Prevalence

BR-BR (N=4,246) BR-BL (N=372) 73% 21% 7% 49% 33% 18% BL-BL (N=143) 50% 33% 17% Also, Dals with one or two blue eyes had more deafness than Dals with only brown eyes.Also, Dals with one or two blue eyes had more deafness than Dals with only brown eyes.

Slide 38:Prevalence of Deafness In Dalmatians By Country

United States 30% (G Strain, N=5,333) UK 21% (M Greening, N=2,282) Holland 18% (B Schaareman, N=1,208) Belgium 19% (L Poncelet, N=122) By contrast to the 30% in the US, other countries have reported lower prevalence rates. 21% in the UK. 18% in the Netherlands. I will discuss later why I think these differences result.By contrast to the 30% in the US, other countries have reported lower prevalence rates. 21% in the UK. 18% in the Netherlands. I will discuss later why I think these differences result.

Slide 39:Impact Of Breed Standards

United States: allows blue eyes Europe & Canada: do not allow blue eyes efforts through breeding to reduce blue eyes in Norwegian Dalmatians also reduced deafness prevalence. So, what accounts for the difference in deafness prevalence between the US and Europe? Enough animals have been tested to assure that accurate rates have been measured. First, the blue eye is allowed in the breed standard in the US. This would seem to favor deafness. Second, the patch is not allowed. Third, and perhaps most important, breeding of unilaterally deaf dogs is not forbidden. This will guarantee high numbers of deaf Dalmatians.So, what accounts for the difference in deafness prevalence between the US and Europe? Enough animals have been tested to assure that accurate rates have been measured. First, the blue eye is allowed in the breed standard in the US. This would seem to favor deafness. Second, the patch is not allowed. Third, and perhaps most important, breeding of unilaterally deaf dogs is not forbidden. This will guarantee high numbers of deaf Dalmatians.

Slide 40:Breeding Recommendations

BEST ADVICE: don't breed affected animals a unilaterally deaf animal is genetically the same as a bilaterally deaf animal, and should not be bred! it is unwise to repeat a breeding that produced large numbers of deaf animals avoid breeding to animals with a history of producing many deaf offspring I recommend the following: 1. Don't breed unilaterally deaf animals. 2. Do not repeat breedings that produced many deaf. 3. Avoid breeding to lines that have produced many deaf. I recommend the following: 1. Don't breed unilaterally deaf animals. 2. Do not repeat breedings that produced many deaf. 3. Avoid breeding to lines that have produced many deaf.

Slide 41:Breeding Recommendations (cont.)

do not totally breed away from patches (Dal)  avoid breeding blue eyed animals if deafness is a problem in your breed, ALWAYS know the hearing status of animals you breed to! breeding decisions should always take into consideration of the overall good of the breed 4. Do not eliminate patched dogs. 5. Do not breed blue-eyed dogs. Make breeding decisions thinking about what is best for the breed, not what might be best for your kennel. 4. Do not eliminate patched dogs. 5. Do not breed blue-eyed dogs. Make breeding decisions thinking about what is best for the breed, not what might be best for your kennel.

Slide 42:Current Research

Slide 43:Canine Genome Project

sequencing of canine genome now a designated priority project of the National Human Genome Research Institute (NIH) and sequencing of the boxer has begun (1.5X sequence of a poodle was just published in Science) expected to cost about $50M microsatellite marker sets now available for whole genome screen studies (MSS1=172, MSS2=327) 3,270-marker canine radiation hybrid linkage map now available

Slide 44:Molecular Genetic Approaches to Identifying Defects Responsible for Deafness

candidate gene approach: sequence dog/cat genes equivalent to ones identified in the mouse or in man that have been shown to be causative for deafness (i.e. mitf, c-kit) whole genome screen approach: use a set of microsatellite markers that cover all dog/cat chromosomes with minimal spacing to identify markers that co-segregate with deafness, then narrow down to specific gene

Slide 45:Study: Molecular Genetics of Deafness

AKC/CHF: Murphy, Strain "Genetics of Hereditary Deafness in the Domestic Dog� 1. examine candidate genes from mouse/human: mitf c-kit 2. DNA collection from affected pedigrees Dalmatian English setter 3. determination of mode of inheritance

Slide 46:Study: Molecular Genetics of Deafness

Results: mitf � not causative for deafness in Dal c-kit � not causative for deafness in Dal mode of inheritance: NOT simple autosomal recessive best modeled as being inherited as a single �locus� but one that does not follow Mendelian genetics

Slide 47:Syndromic and nonsyndromic human hearing loss loci

Slide 48:Other Ongoing Molecular Genetic Studies

AKC/CHF - Murphy, Strain: "Whole genome screens using microsatellite markers in genetic analyses of hereditary deafness in the Dalmatian and English Setter� 1. pedigree of >200 Dalmatians with DNA 2. English setter DNA pedigree being assembled 3. whole-genome screens underway JRT Research Foundation - Strain: �Assembly of a DNA pedigree for whole genome screens for hereditary congenital deafness in the Jack Russell Terrier� further funding being sought

Slide 49:Other Ongoing Molecular Genetic Studies

University of Pennsylvania: genetics of deafness in �nervous� pointers (Steinberg) Michigan State University: candidate gene studies of deafness in various dog breeds (Yuzbasiyan-Gurkan) Europe: candidate gene studies and whole genome screen studies of canine deafness (Distl, Dolf) Cat studies: none known of at present

Slide 50:References:

Strain GM. Deafness in Dogs & Cats web page: www.lsu.edu/deafness/deaf.htm Strain GM. 2003. Deafness prevalence and pigmentation and gender associations in dog breeds at risk. The Veterinary Journal (in press). Strain GM. 1999. Congenital deafness and its recognition. Vet Clin N Amer: Small Anim Pract 29:895-907. Strain GM. 1996. Aetiology, prevalence and diagnosis of deafness in dogs and cats. British Veterinary Journal 152:17-36. Little CC. 1957. The Inheritance Of Coat Color in Dogs. Howell Book House: New York. 194 pp. Searle AG. 1968. Comparative Genetics of Coat Colour In Mammals. Logos Press/ Academic Press: London. 310 pp. These references provide further information. The first is an Internet web page I created that has much of this information on it.These references provide further information. The first is an Internet web page I created that has much of this information on it.

Slide 51:This cartoon shows just how important hearing can be for a dog. (Gerold - I may not use this - I don't know if people would understand the humor from another language: the rhyme of neuter and tutor.)This cartoon shows just how important hearing can be for a dog. (Gerold - I may not use this - I don't know if people would understand the humor from another language: the rhyme of neuter and tutor.)