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Deafness in Dogs. Causes, Prevalence, and Current Research. George M. Strain Louisiana State University Baton Rouge, Louisiana USA. Forms of Deafness. inherited or acquired congenital or later-onset sensorineural or conductive

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slide1
Deafness in Dogs

Causes, Prevalence, andCurrent Research

George M. Strain

Louisiana State University

Baton Rouge, Louisiana USA

slide2
Forms of Deafness
  • inherited or acquired
  • congenital or later-onset
  • sensorineural or conductive
  • Result: eight possible combinations (i.e., acquired later-onset sensorineural deafness)
slide3

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
slide5
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
slide9
Dog Breeds With Congenital Deafness
  • reported in over 80 dog breeds
  • prevalence (unilateral and bilateral) worst in:
  • Dalmatian (n=5,333) 30%
  • white Bull Terrier (n=346) 20%
  • English Setter (n=3,656) 8%
  • Australian Cattle Dog (n=296) 15%
  • English Cocker Spaniel (n=1,136) 7%
  • Jack Russell Terrier (n=56) 16%*
  • Catahoula Leopard Dog (n=78) 63%*
slide10
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
slide16
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
slide18
Dalmatian Deafness Prevalence in the US

N=5,333

70.1% (3,740)

21.9% (1,167)

8.0% (426)

slide19
Prevalence of Deafness In Dalmatians By Country
  • United States 30% (G Strain, N=5,333))
  • United Kingdom 21% (M Greening, N=2,282)
  • Holland 18% (B Schaareman, N=1,208)
slide20
Effect of Parent Hearing Status On Deafness Prevalence

B-U Parents (N=728)

B-B Parents (N=2,320)

73%

59%

31%

21%

11%

6%

slide21
Effect of Sex On Deafness Prevalence

Male (N=2,459)

Female (N=2,424)

69%

71%

22%

22%

7%

9%

slide22
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
slide23
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)
slide24
Effect of Patch On Deafness Prevalence

Not Patched (N=4,404)

Patched (N=436)

90%

68%

23%

9%

8%

2%

slide25
Effect of Eye Color (Brown or Blue) On Deafness Prevalence

BR-BR (N=4,246)

BR-BL (N=372)

BL-BL (N=143)

73%

49%

50%

33%

33%

21%

18%

17%

7%

slide26
Effect of Retinal Pigmentation On Deafness Prevalence

Pigmented (N=2,611)

Not Pigmented (N=623)

71%

56%

29%

22%

15%

7%

slide27
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.
slide28
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
slide29
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
slide30
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 154:121, 1997
  • 4-5 generations of selective breeding would probably be necessary for a detectable impact on overall prevalence.
slide32
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
slide33
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)
slide34
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
slide35
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
other ongoing molecular genetic studies
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
slide37
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.
slide39
Deafness in Dogs & Cats Web Site:

www.lsu.edu/deafness/deaf.htm

strain@lsu.edu