Some dogs lose their hearing because of an ear infection. Some suffer an injury, some react badly to certain drugs, and some just succumb to old age. Exposure to loud sounds can also cause temporary or permanent deafness, We’ve read, however, that the most common cause of congenital deafness (meaning from birth) is pigment related, and that some 30 breeds are said to have a known susceptibility for deafness for that reason.
Merle is a dominant gene. A dog needs only one copy to have a merled coat. Dogs with two copies of the merle gene are referred to as having a “Double Merle.” Double Merle pups are born when both of the parents are merle (it doesn’t matter what color or breed). Statistically, 25% of the pups from two merle parents
will be Double Merles. When the dog has two copies, instead of producing only partial lightening, the effect is doubled, causing some to most of the coat to turn white. These dogs are also sometimes referred to being “lethal whites,” a term that came to be used with double merle’s because these puppies were sometimes euthanized at birth by breeders who knew they could be deaf and/or blind (read: it pays to work with an ethical breeder who knows their breed and what they’re doing).
From the http://www.doublemerles.info/ website:
“Some dogs are naturally white such as Samoyeds, Bichons, and West Highland Terriers. These dogs were created to be white and as a result their skin is pigmented. The fur will appear white, but the skin underneath is pigmented along with the nose and eye rims.
The merle gene whitens and take the skin pigment with it. When that gene is doubled, it pulls even more pigment from the skin.
If the dog lacks pigment in the inner ear, the tiny little hairs/nerve endings will fall off and die very early in the dogs life. This occurs within the first 3 weeks of the dogs life. The inside of the dogs ear along with the tiny hair is not something that can be seen. It’s often said that dogs with white ears will be deaf, but this is not always the case.”
Image found on Pinterest and cheerfully credited upon receipt of information.