Deafness and Hearing Loss
Due to the decreased pigment, double merles are at a high risk for deafness and hearing impairment. Most are faced with some sort of hearing impairment. Most a bilaterally deaf, meaning completely deaf. Some can be unilaterally deaf with hearing in one ear. Others can hear different volumes and pitches, but not a normal speaking volume. It is possible for double merles to have normal hearing.
Double merles are born with or without their hearing deficiencies. If your double merle loses hearing later in life, it would be as a result of something unrelated to it being a double merle, such as old age or infection.
Some dogs are naturally white such as Samoyeds, Bichons, and West Highland Terriers. These dogs were bred to have white coats, but 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 blocks pigment from appearing in areas on the skin, as well as the fur. When that gene is doubled, it blocks even more pigment. 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. The inside of the dog's ear, along with the tiny hair is not something that can be seen from the outside of the dog. It's often said that dogs with white ears will be deaf, but this is not always the case.