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

Result: eight possible combinations (i.e.,
acquired later-onset sensorineural
deafness)
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
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

Dog Breeds With Congenital Deafness
reported in over 80 dog breeds
 prevalence (unilateral and bilateral) worst in:

Dalmatian (n=5,333)
 white Bull Terrier (n=346)
 English Setter (n=3,656)
 Australian Cattle Dog (n=296)
 English Cocker Spaniel (n=1,136)
 Jack Russell Terrier (n=56)
 Catahoula Leopard Dog (n=78)

30%
20%
8%
15%
7%
16%*
63%*
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
Brainstem Auditory Evoked Response
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

Demi Azure Pedigree
6 (5)
12 (11)
Dalmatian Deafness Prevalence in the US
80
N=5,333
70.1% (3,740)
70
Percent
60
50
40
21.9% (1,167)
30
20
8.0% (426)
10
0
Bilateral
Unilateral
Deaf
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)
Effect of Parent Hearing Status On
Deafness Prevalence
B-B Parents (N=2,320)
80
73%
70
59%
60
Percent
B-U Parents (N=728)
50
40
31%
30
21%
20
11%
6%
10
0
Bi
Uni
Deaf
Bi
Uni
Deaf
Effect of Sex On Deafness Prevalence
Male (N=2,459)
Female (N=2,424)
80
70
69%
71%
Percent
60
50
40
30
22%
22%
20
7%
10
9%
0
Bi
Uni
Deaf
Bi
Uni
Deaf
Coat Pigmentation Genes In The
Dalmatian
Base coat - underlying coat color
B - black (dominant)
b - liver (recessive)
w - white covering,
 Extreme piebald gene - s
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

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)
Effect of Patch On Deafness Prevalence
Not Patched (N=4,404)
Patched (N=436)
100
90
90%
80
68%
Percent
70
60
50
40
30
23%
20
8%
10
0
Bi
Uni
9%
2%
Deaf
Bi
Uni
Deaf
Effect of Eye Color (Brown or Blue) On
Deafness Prevalence
BR-BR (N=4,246)
80
BR-BL (N=372)
BL-BL (N=143)
73%
70
Percent
60
49%
50
40
50%
33%
33%
30
21%
20
18%
17%
7%
10
0
Bi
Uni
Deaf
Bi
Uni
Deaf
Bi
Uni
Deaf
Effect of Retinal Pigmentation On
Deafness Prevalence
Pigmented (N=2,611)
Not Pigmented (N=623)
80
70
71%
56%
Percent
60
50
40
29%
30
22%
20
15%
7%
10
0
Bi
Uni
Deaf
Bi
Uni
Deaf
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.
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

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
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.
Current Research
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

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)

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

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
• 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
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.

Deafness in Dogs & Cats Web Site:
www.lsu.edu/deafness/deaf.htm
strain@lsu.edu