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Deafness in Dogs

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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Deafness in Dogs

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  1. Deafness in Dogs Causes, Prevalence, andCurrent Research George M. Strain Louisiana State University Baton Rouge, Louisiana USA

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

  3. 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

  4. 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

  5. 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%*

  6. 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

  7. Brainstem Auditory Evoked Response

  8. 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

  9. Demi Azure Pedigree 6 (5) 12 (11)

  10. Dalmatian Deafness Prevalence in the US N=5,333 70.1% (3,740) 21.9% (1,167) 8.0% (426)

  11. 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)

  12. 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%

  13. Effect of Sex On Deafness Prevalence Male (N=2,459) Female (N=2,424) 69% 71% 22% 22% 7% 9%

  14. 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

  15. 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)

  16. Effect of Patch On Deafness Prevalence Not Patched (N=4,404) Patched (N=436) 90% 68% 23% 9% 8% 2%

  17. 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%

  18. Effect of Retinal Pigmentation On Deafness Prevalence Pigmented (N=2,611) Not Pigmented (N=623) 71% 56% 29% 22% 15% 7%

  19. 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.

  20. 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

  21. 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

  22. 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.

  23. Current Research

  24. 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

  25. 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)

  26. 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

  27. 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

  28. 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

  29. 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.

  30. Deafness in Dogs & Cats Web Site: www.lsu.edu/deafness/deaf.htm strain@lsu.edu

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