Pets with white coats and blue eyes can be striking, but praising such pets on their pretty looks might fall on deaf ears — literally. The association between blue eyes, white coats and deafness has been noted since the early 1800s. In fact, even Charles Darwin brought it up in his 1859 book, The Origin of the Species. While the genetic link is not new, our deeper understanding of the phenomenon is relatively recent, thanks in part to research findings about the way genes regulate coat and eye color.
There are several kinds of deafness, but the kind that is linked to coat color is termed “sensorineural deafness,” and it is congenital (present at birth). Deafness in these pets is associated with a dominant merle or white gene in many breeds, including the Collie breeds, Dachshunds, Great Danes and Shetland Sheepdogs, as well as many breeds of cat.
In dogs and cats with white-producing genes, deafness appears to result from a strong expression of that gene. When the merle or white gene is strongly expressed, it suppresses not only the pigment-producing cells in the skin, but also the pigment-producing cells in the eyes, leading to blue eyes. The white gene will also cause the absence of certain cells in the ear, which leads to the death of tiny sound-detecting hairs, the collapse of various inner ear structures, and the degeneration of nerve fibers in the ear. All of this leads to hearing loss by about five weeks of age in affected pets.
The good news is, deaf pets can live their lives with the same joy and fullness as hearing pets. But because this type of deafness is hereditary, pets at risk of carrying white and merle-producing genes should be hearing-tested before being bred.