DeafTalk

Information about DeafTalk

Published on November 16, 2007

Author: Javier

Source: authorstream.com

Content

Slide1:  Deafness in Dogs George M. Strain Louisiana State University Baton Rouge, Louisiana USA Causes, Prevalence, and Current Research 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:  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 Definitions 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 Slide15:  Brainstem Auditory Evoked Response 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 Slide17:  Demi Azure Pedigree 6 (5) 12 (11) 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-B Parents (N=2,320) B-U Parents (N=728) 73% 21% 6% 59% 31% 11% Slide21:  Effect of Sex On Deafness Prevalence Male (N=2,459) 71% 22% 7% 69% 22% 9% Female (N=2,424) 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 Patched (N=436) Not Patched (N=4,404) 90% 8% 2% 68% 23% 9% Slide25:  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% Slide26:  Effect of Retinal Pigmentation On Deafness Prevalence Pigmented (N=2,611) 71% 22% 7% 56% 29% 15% Not Pigmented (N=623) 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. Slide31:  Current Research 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 [email protected]

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