Hereditary Deafness in Dogs
By Sharon Schaefer
The only hereditary deafness known in dogs is early onset, so one hearing screening (BAER/P) is good for life and it can be done as early as 5 weeks of age. Unfortunately for Icelandic fanciers a majority of deafness in dogs is connected to the various white patterning alleles of the S series - si (Irish spotting), sp (piebald), and sw (extreme white) are all implicated through various different breeds although sp and sw are more prevalent.
Studies have not been done in Icelandics and there is no reported puppy deafness. As more breeders continue to work with and produce higher white factor puppies the greater the chance of this changing.
Unfortunately again, the experience of other breeds is that unilaterally (one ear only) deaf pups cannot be identified by any simple means - they cope very well and even bilaterally deaf pups mimic their littermates. Even breeders experienced in identifying deafness need to isolate the pup and create a slight sound out of sight.
If there is any air current created or sound vibration the pup may respond to that so that a bilaterally deaf puppy can behave to us as though it hears.
The genetics that produce white hair and skin also suppresses the pigment cells in the cochlea inside the ear. The cochlea converts sound into nerve impulses through the vibrations of tiny hairs. When the pigment cells do not develop this interferes with the formation of cochlear hairs and neurons. When there are no cochlea hairs, deafness occurs.
Pigment-associated hereditary deafness (this alsorefers to deafness associated with the Merle gene which does not occur in Icelandics so will not be discussed in this article) is a secondary deafness occurring about 2-4 weeks after birth. It is caused when the nourishing bed (striavascularis) for the tiny hairs of the inner ear breaks down resulting in death of the hair cells and deafness. The mode of inheritance is not identified in any of the breeds studied but in the Dalmatian it appears to be single locus but with incomplete penetrance through action of an unknown number of other genes.
Genetically, unilateral deafness is bilateral deafness that is not completely expressed so no deaf dogs, whether one or both ears, should be used in breeding. As with other hereditary diseases breeders should also avoid repeating a breeding that produced a deaf puppy.
The Brainstem Auditory Evoked Response is an objective test which identifies hearing in each ear through the use of four electrodes and ear plugs. A click is generated through one ear for 2 minutes while brain waves are read by a computer. The test is not painful and with patient and firm handling to stay still for 2 minutes (then 2 more minutes for the other ear) most dogs are quite comfortable with the procedure. A printout of the waveform is provided to the owner. In Canada, this test is available at each of the four veterinary universities as well as privately in Scarborough, ON and through the Calgary Dog Fanciers Association.
Addresses are on the Dalmatian Club page. The equipment can be moved to different locations and some breed clubs sponsor clinics in various locations. The price this year at one university was just over $100 for the first pup then about $40 for each littermate Interestingly, albinism does not have any association with deafness, nor do other genes reported to produce white or light coat color in dogs - flecking, ticking, or dilution with fawn.
In other breeds white patterning (occurring from an absence of melanocytes) together with blue eyes significantly increases the chance of deafness. When the white pattern gene is more strongly expressed it suppresses melanocytes not only in the skin but also in the iris of the eye and the stria of the ear.
Not all deaf animals have blue eyes and not all blue eyed dogs are deaf but there is a statistically significant link so breeding to blue-eyes animals is not recommended for most breeds.
For example, blue eyes are not allowed in the Dalmatian standard in Europe but they are allowed in the US. The incidence of deafness is 50% higher in the US Dalmatian population.
Working in the other direction, Dalmatians with a patch of colour are less likely to be deaf than the average. This association holds true in other studied breeds.
So that less than 2% of Coloured Bull Terriers are deaf while just under 20% of White Bull
Terriers are deaf (sample size over 600).
Several universities in the USA and Europe are currently working with different breeds in attempts to identify the molecular DNA level mechanisms for inherited deafness in dogs but they have not yet been successful.
www.btca.com/Health/health.html
www.dalmationclubofcanada.ca/deafness.html
www.lsu.edu/deafness/baerexpl.htm
www.lsu.edu/deafness/Tufts.htm
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