Deaf dogs – Why are they deaf?

Deaf dogs – Why are they deaf?

There are four main reasons why a dog cannot hear. The reasons are:
loss of hearing due to old age, illness, injury and deaf at birth
(congenital deafness). The first three causes of deafness are
individual to each dog and not hereditary. Congenital deafness may be
unique to an individual or it may be inherited. Non-inheritable
congenital deafness may be the result of a drug toxicity or illness
of the dog’s pregnant mother.

Congenital deafness means that during the development of the dog in
the womb, the tissues needed to form an entire working ear and its
nerves did not form normally. The outer parts of the ear are present
and the puppy looks normal. Inside the ear, it is another story. The
blood supplies to nerve tissue in the inner ear degenerate shortly
after birth. This means that the sounds that reach the pup’s outer
ear, eardrum, middle ear and inner ear cannot be sent on to the brain
To understand why some dogs are deaf and others in the same litter
hearing, a few more details are needed about how dogs develop inside
their mother’s womb. Shortly after conception, the fertilized egg
begins to develop into a variety of cells that will form the
precursors to all the cells a dog will ever need to be a dog. Some of
these cells are called melanocytes. These cells will change into two
important types of cells – those that form the nervous tissue and
those that form the cells that give colour to hair, skin, eyes, etc.
If there are not enough melanocytes, a dog will potentially not have
enough nerves to do certain work or enough pigment in the skin, hair,
eyes, etc. The lack of melanocytes can be partial (the dog has some
hearing) or complete (the dog has no hearing). One or both ears may
be affected.

To complicate the story, there are different kinds of “white” that
are controlled by different genes in dogs and some genes control
where the white is located (pattern of colour on the dog). Genes for
coat colour that are intricately linked to deafness are the merle
genes and piebald genes. Merle genes produce the dappled or merle
effect of multicoloured individual hairs. Piebald genes affect the
amount and distribution of white on the dog’s coat. How these coat
colour genes interact to produce deaf dogs is complicated and not
fully understood. Many years of observation of a variety of dog
breeds indicate that there is a connection between the amount and
distribution of white on the dog and congenital deafness. This does
not mean all deaf dogs have white heads nor does it mean that dogs
with externally dark coloured ears or heads will have hearing.

The inheritance of deafness is related to the genetic “package” that
the dog’s parents bring to the litter. If the parents have hearing
and overly white heads, for their breed, and/or they are both merle
dogs and/or they are both very white piebald, or they are
congenitally deaf due to lack of pigment, the probability of
producing deaf pups is much higher. If a dog is deaf due to illness,
injury or because nature made a mistake during the development of the
dog in the womb, then pups produced from that dog are no more likely
to be deaf than any other pup.

Author: Heather Pate, member of DDEAF
Deaf-initely Dogs, Spring 2002 Edition
The official newsletter of Deaf Dog Education Action Fund
www.ddeaf.org

While, as in Danes, Dobermans, and other breeds, a pure white coat indicates albinism and possibly deafness and sight deficiency, a white coat in the German Shepherd Dog is not a new mutation but a normal coat type that has been around since the breed was established in Germany. White Shepherds are not associated with any health problems that are not present in other GSDs, and are not albinos in any degree. They have, like any other Shepherd: dark eyes, black noses, hearing, and pigmented skin. The reason they are not allowed in conformation in the United States is because, in Germany, as the breed was developing, some dogs were being found that had paler coats than was desired. Misunderstanding the genetics of the GSD, fanciers blamed the white dogs for causing these patterns, and amended their breed standard to exclude all white dogs.