Piebald or Extreme Piebald Gene – DeafnessLiaison: Hazel Fitzgibbon
Piebald is defined as ‘having patches of black and white or of other colors; parti-colored’ (Dictionary.com). In piebald animals this happens through the effect of the piebald gene ‘covering,’ in some or all areas, the effect of another gene for an underlying coat color. Samoyeds are said to have two copies of the extreme piebald gene (Little 1967). For many years deafness has been associated with this colour pattern, as well as with Merle.
One mechanism connecting lack of colour and deafness has now been identified. There are small hairs in the inner ear called cilia. In the puppy who will hear, these hairs develop normally. If the extreme piebald gene is present, pigment cells (melanocytes) are suppressed and these hairs may not develop properly.
“It has been shown in mice that the presence of pigment cells is essential for normal inner ear development. They normally colonize the stria vascularis. However, in their absence, as is also well documented in the dog, the stria vascularis degenerates. As this provides the blood supply to the cochlea, damage to this structure occurs and the sensory hair cells necessary for hearing die.” (quote from: http://www.steynmere.com/DALM_DEAFNESS2.html)
There is as yet no definitive proof that the extreme piebald gene is associated with hereditary deafness in Samoyeds. A lot of very persuasive work has been done on deafness in Dalmatians and Border Collies, other breeds who carry this gene.
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Signs and Symptoms
A deaf baby puppy may exhibit signs including;
- Not following siblings cries when feeding, thus they may not get enough food and may not thrive well.
- Irritability towards siblings - being unable to hear audible communications.
- Non reactive to loud noises.
An adult may also exhibit fear biting as the result of a deaf dog being startled.
Deafness associated with piebald coloring is inherited in some breeds, but the presence of the gene by itself is not sufficient to cause deafness. For example, all Dalmatians have two copies of the extreme piebald gene (homozygous), but not all of them are deaf – there appear to be other genes involved as well.
However, it is important to eliminate other causes for deafness before coming to a conclusion that your animal is deaf due to the extreme piebald gene. Deafness in Samoyeds is not common, but may be attributed to any of the following, or a combination thereof;
- Congenital (present at birth) - Genetic (hereditary)
- Congenital (present at birth) - Acquired (for example, dam exposed to toxic drug)
- Otitis (inflammation) through bacteria or fungal infections in Inner or Outer Ear
- Injury by accident or foreign body invasion
- Old age (Presbycusis)
- Drug Toxicity including General Anaesthesia
- Noise Trauma
The BAER test is an extremely reliable, objective test used to determine if a dog is deaf in one or both ears. If the deafness is partial, it can also measure the extent of hearing loss. BAER stands for "Brainstem Auditory Evoked Response." It is a procedure using computer-regulated sensors to record the electrical activity of the brain in response to sound stimulation. Electrodes are put just under the skin, but these do not seem to bother most dogs.
Contrary to popular belief, puppies are not ‘born deaf’. Puppies are born with a covering across the ear which prevents sound from reaching the functioning hearing organs. In normal development, this disintegrates about the same time as eyes open. The BAER test can only be performed after this happens, once a puppy is 4-5 weeks old.
The piebald gene in dogs has recently been located on dog chromosome 20 and identified as “Mitf.” Researchers are looking for other genes associated with deafness in dogs carrying the extreme piebald gene. At the time of writing, there is no genetic test for hereditary deafness in Samoyeds.
Note: Treatment of animals should only be performed by a licensed veterinarian. Veterinarians should consult the current literature and current pharmacological formularies before initiating any treatment protocol.
With congenital deafness, there is no cure.
While congenital deafness does not cause pain, it is the repercussions that are limiting, even dangerous. Deafness poses a problem in that it can’t be seen by breeders or owners. While you can accommodate a blind dog quickly as the disability is fairly obvious, a deaf dog is not so obvious. Dogs adapt very well to losing a sensory organ and try to fill in the loss by augmenting their other senses.
Dogs who are deaf in one ear can usually lead a relatively normal life. Dogs who are deaf in both ears can be a danger to themselves if not managed properly. One thing that appears and re-appears on sites of different breeds is that a deaf dog cannot hear a car coming. Ensuing injuries cause distress to the dog and owner.
Deaf dogs can be trained to follow hand signals, instead of voice commands.
Affected dogs should not be bred. Matings that produce deaf dogs should not be repeated.
Karlsson, Elinor, et al of the Broad Institute of Harvard and MIT,. "Two-stage association mapping in dogs identifies coat color locus," presented at the Third International Conference on Advances in Canine and Feline Genomics, held in Davis, CA, August 2-5, 2006. The paper is expected to be published in a future issue of the Journal of Heredity
Leaflet explains a lot of the basics of deafness
http://www.lancedal.demon.co.uk/health/gstrain.htm -- Explains how extreme piebald gene may relate to other genes to cause deafness
Little, Clarence C. 1967. The Inheritance of Coat Color in Dogs. Howell Book House.
A comprehensive list of references for deafness in dogs