Why White Cats Are Affected
Congenital deafness in cats is closely tied to the dominant white gene (W), which does more than remove colour from the coat. The same gene can influence eye colour and interfere with the pigment cells that the inner ear needs to develop properly. When those cells are missing, part of the hearing organ can degenerate in the first weeks of life. This is why a solid white cat carries a higher risk of being born deaf than a cat of any other colour.
The Link to Eye Colour
A cat's eye colour offers a useful clue to its risk, though it never replaces an actual test. A white cat with two blue eyes is several times more likely to be deaf than one with ordinary eye colour. An odd-eyed cat, with one blue eye, sits in between, and any deafness often affects the ear on the same side as the blue eye. A cat can also be deaf in just one ear, which is easy to miss in daily life yet still passes the trait to kittens.
What a BAER Test Measures
BAER stands for Brainstem Auditory Evoked Response, and it is the most dependable way to check a cat's hearing. Small sensors on the head record the brain's electrical response while gentle clicks are played into each ear separately. Because it tests one ear at a time, it reveals one-sided deafness that a casual observation would never catch. The whole thing is safe and painless, takes only a few minutes, and can be done awake or with light sedation depending on the cat.
Testing Before You Breed
Any white cat intended for breeding should be BAER tested first, because even a cat that hears on one side can pass deafness on to its kittens. Many breed registries require hearing testing for white breeding cats and do not permit breeding from deaf cats, with BAER as the recommended method. Testing protects the kittens you produce and the families who will welcome them. If you buy a white kitten, it is always fair to ask the breeder whether the parents were hearing tested.