Deafness in Dogs

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• Deafness in Dogs

Causes, Prevalence, andCurrent Research
George M. Strain Louisiana State University Baton
Rouge, Louisiana USA
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• Forms of Deafness

• inherited or acquired
• congenital or later-onset
• sensorineural or conductive
• Result eight possible combinations (i.e.,
  acquired later-onset sensorineural deafness)

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Definitions

• sensorineural deafness - loss of function because
  of loss of cochlear hair cells or cochlear nerve
  neurons
• conductive deafness - blockage of sound
  transmission through outer and/or middle ear
  without damage to cochlea

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• Inherited Congenital Sensorineural Deafness

• usually associated with the genes responsible for
  white hair
• piebald gene (sp) and extreme piebald (sw) gene
• merle (M) gene
• deafness develops at 3-4 weeks of age after the
  blood supply to the cochlea (stria vascularis)
  degenerates
• strial degeneration is thought to result from
  absence of pigment cells (melanocytes)
• other pigmentation effects are frequently seen

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• Dog Breeds With Congenital Deafness

• reported in over 80 dog breeds
• prevalence (unilateral and bilateral) worst in
• Dalmatian (n5,333) 30
• white Bull Terrier (n346) 20
• English Setter (n3,656) 8
• Australian Cattle Dog (n296) 15
• English Cocker Spaniel (n1,136) 7
• Jack Russell Terrier (n56) 16
• Catahoula Leopard Dog (n78) 63

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• Hearing Testing

• behavioral testing - sound stimuli outside of the
  animal's visual field
• cannot detect unilateral deafness
• animals quickly adapt to testing
• detected through other sensory modalities
• electrodiagnostic testing - brainstem auditory
  evoked response (BAER)
• objective, non-invasive
• detects unilateral deafness
• limited availability

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• Brainstem Auditory Evoked Response

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• Genetics of Congenital Deafness

• Doberman - simple autosomal recessive
• pigment-associated deafness in dogs - most likely
  polygenic, incomplete penetrance, or other
  mechanism NOT simple autosomal recessive
• merle gene - dominant homozygous dogs have
  additional health problems
• piebald genes - recessive, but all dogs in the
  breed are homozygous

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• Demi Azure Pedigree

6 (5)
12 (11)
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• Dalmatian Deafness Prevalence in the US

N5,333
70.1 (3,740)
21.9 (1,167)
8.0 (426)
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• Prevalence of Deafness In Dalmatians By Country

• United States 30 (G Strain, N5,333))
• United Kingdom 21 (M Greening, N2,282)
• Holland 18 (B Schaareman, N1,208)

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• Effect of Parent Hearing Status On Deafness
  Prevalence

B-U Parents (N728)
B-B Parents (N2,320)
73
59
31
21
11
6
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• Effect of Sex On Deafness Prevalence

Male (N2,459)
Female (N2,424)
69
71
22
22
7
9
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• Coat Pigmentation Genes In The Dalmatian

• Base coat - underlying coat color
• B - black (dominant)
• b - liver (recessive)
• Extreme 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

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• Effect of the Extreme Piebald Gene

• Weak gene expression failure of the piebald gene
  to completely suppress the underlying coat color
  (black or liver) results in a patch
• Strong gene expression suppresses pigmentation
  in the iris (blue eyes) and tapetum (red eye),
  and in the stria vascularis (deafness)

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• Effect of Patch On Deafness Prevalence

Not Patched (N4,404)
Patched (N436)
90
68
23
9
8
2
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• Effect of Eye Color (Brown or Blue) On Deafness
  Prevalence

BR-BR (N4,246)
BR-BL (N372)
BL-BL (N143)
73
49
50
33
33
21
18
17
7
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• Effect of Retinal Pigmentation On Deafness
  Prevalence

Pigmented (N2,611)
Not Pigmented (N623)
71
56
29
22
15
7
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• Impact Of Breed Standards

• United States allows blue eyes
• Canada does not allow blue eyes
• Europe does not allow blue eyes
• Efforts through breedings to reduce blue eyes in
  Norwegian Dalmatians also reduced deafness
  prevalence.

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• 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 breedings that produced
  large numbers of deaf animals
• avoid breeding to animals with a history of
  producing many deaf offspring

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• Breeding Recommendations (cont.)

• do not totally breed away from patches - possibly
  accept in the breed standard
• avoid breedings to blue eyed animals
• ALWAYS KNOW THE HEARING STATUS OF DOGS YOU BREED
  TO!
• BREEDING DECISIONS SHOULD ALWAYS TAKE INTO
  CONSIDERATION THE OVERALL GOOD OF THE BREED

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• Possible Impact of Selective Breeding

• a recent study by Wood Lakhani suggested that
  selective breeding against unilaterally and
  bilaterally deaf animals could reduce deafness to
  below 15 and 4 respectively. The Veterinary
  Journal 154121, 1997
• 4-5 generations of selective breeding would
  probably be necessary for a detectable impact on
  overall prevalence.

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• Current Research

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• Study Molecular Genetics of Deafness

• AKC/CHF Murphy, Strain "Genetics of Hereditary
  Deafness in the Domestic Dog"
• candidate genes
• mitf
• c-kit
• DNA collection from affected pedigrees
• Dalmatian
• English Cocker Spaniel
• English Setter
• determination of mode of inheritance

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• Study Molecular Genetics of Deafness

• mitf
• human homolog of the mouse microphthalmia (mi)
  gene
• responsible for 20 of cases of Waardenburg
  Syndrome type 2 in humans
• regulates the expression of several pigment genes
• necessary for transition of precursor cells to
  melanoblasts (which become melanocytes)

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• Study Molecular Genetics of Deafness

• c-kit
• tyrosine kinase receptor
• activation of the c-kit receptor regulates mitf
  function
• mutations result in the absence of melanocytes
  and functional mast cells, as well as defects in
  ova and sperm development and blood cell
  formation
• gene defects in mice produce dominant white
  spotting and deafness
• gene defects in humans produce piebaldism and
  occasionally deafness

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• Study Molecular Genetics of Deafness

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

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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
• pedigree of 200 Dalmatians with DNA
• English setter pedigree being assembled
• whole-genome screens underway
• further funding being sought from NIH CHF

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• References

• Strain GM. Deafness in Dogs Cats web page
  www.lsu.edu/deafness/deaf.htm
• Strain GM. 1996. Aetiology, prevalence and
  diagnosis of deafness in dogs and cats. British
  Veterinary Journal 152 (1) 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.

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• Deafness in Dogs Cats Web Site
• www.lsu.edu/deafness/deaf.htm
• strain_at_lsu.edu