What is the link between white dogs and deafness?

white-deaf-dog

By Mary Beth Miller

Did you know that dogs with predominantly white coats can be prone to deafness? Approximately 85 different dog breeds have been reported to carry the trait that causes congenital deafness.

Deafness is defined as a loss of hearing caused by a delivery interruption of sound to the brain. When sound waves reach the eardrum, it vibrates like a big gong, causing the middle ear bones (or “ossicles”) to vibrate as well. These vibrations reach the fluid-filled, spiral-shaped cochlea of the inner ear, creating waves.

All this commotion causes a pressure change and forces the cochlea’s hair cells to move. These hair cells are connected to the auditory (hearing) nerves, which sparks a nerve impulse down the auditory pathway that connects to the brain. (For more detailed info on the structure of the ear, click here.)

What does a white coat have to do with hearing loss? The ability to hear is made possible by a special layer of cells within the inner ear. This specialized layer of cells, and the cells that determine hair color, come from the same stem cell source. Without this stem cell, the dog’s body won’t be able to make this specialized layer of hearing cells and will likely be white in coloration.

Dogs that carry the piebald gene are often affected by deafness. Piebaldism results from the absence of melanocytes, the cells that create the pigment melanin. These melanocytes are the part a dog’s DNA that determines coloration, such as brown or black hair, or blue or brown eyes. (Blue eyes are not a true eye color, but rather result from the lack of color-producing pigment within the iris.) When a dog is born without melanocytes, a predominantly white coat (and often blue eyes) is the result. Breeds commonly affected by the piebald gene include Bull Terriers, Boxers, English Setters, and Dalmatians.

Congenital deafness is also linked to the merle gene, which causes a dog to have a merle (or dapple) coat and blue eyes.  Breeds commonly affected by the merle gene include Old English Sheepdogs, dapple Dachshunds, Welsh Corgis, and Border Collies.

The only way to effectively test a dog’s hearing is through a Brainstem Auditory Evoked Response (BAER) test, which evaluates the components of the external ear canal, middle/inner ear cavities, cranial nerve, and selected areas of the brainstem. Electrodes are attached to the skull to measure the electrical activity within the brain, a series of clicks are passed through headphones placed over or in the dog’s ears, and the responses recorded. If there is a hearing deficit, the BAER response is absent (flat line) or reduced in amplitude. BAER tests can determine whether a dog is deaf in one (unilateral deafness) or both ears (bilateral deafness). Note: tests performed on puppies younger than six weeks of age can produce false positive results.

If you suspect that your dog is deaf (regardless of coat and eye color), talk to your veterinarian about performing a BAER test and the appropriate steps and training to help your dog live a happy, normal life.

Learn more about dog genetics and coat markings here. 

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mary-beth-miller-pawedinMary Beth Miller is a registered veterinary technician from southeast Iowa. She works in a large/small animal veterinary clinic and also volunteers at the local Humane Society, Emergency Animal Care Center, as well as the Iowa Parrot Rescue. Her passion lies in helping save the lives of animals. Mary Beth has three dogs, a Siberian husky named Rocky and two rescue dogs named Sambita and Nina.

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