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Deafness in Dogs

Explore inherited and acquired forms of deafness in dogs, including genetic factors, prevalence in various breeds, testing methods, and breeding recommendations to reduce deafness prevalence. Learn about the impact of coat pigmentation genes and breed standards on deafness. Stay informed on current research efforts.

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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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