If you own a white cat, you most likely love his striking snowy coat and bright eyes. But you might also know that these brilliant features have implications that go deeper than appearance. Congenital deafness — present from birth — is seen almost exclusively in white-coated cats. The deafness might affect one ear or both and will almost always be evident within several weeks of birth.
“In particular, there is a very strong relationship between deafness and white cats with blue eyes,” says Brian Collins, DVM, section chief of the Community Practice Service at Cornell University College of Veterinary Medicine.
Limited Awareness. Researchers have found that 17 to 22 percent of white cats without blue eyes are born deaf. The percentage rises to 40 percent if the cat has one blue eye, while 65 to 85 percent of all-white cats with both blue eyes are deaf.
About half of the owners of white cats Dr. Collins meets are aware of the strong link between deafness and coat and eye color. Awareness tends to be lower among those adopting pets from shelters and rescues, versus those purchasing specific breeds. “With newly adopted deaf pets, sometimes people aren’t aware at first that the pet is deaf.”
White skin and hair color are believed to be caused by the dominant white gene (called W) in cats. They occur when the W gene suppresses pigment cells known as melanocytes. The vascular system of a cat’s inner ear structures also contains melanocytes, which likely help maintain the high potassium levels of the fluid surrounding the sensory hair cells in the ear, says George M. Strain, Ph.D., a leading veterinary researcher on deafness and professor of neuroscience at Louisiana State University School of Veterinary Medicine.
When sound waves bend the inner ear hair cells, they open special channels that allow potassium into the cell. The potassium influx excites the hair cell, which in turn triggers the nerve cell that enters the brain in the auditory nerve. If high potassium levels are not maintained around the hair cells, they die and deafness results.
When the W gene suppresses the melanocytes in the ear, the vascular system in the ear degenerates, and the death of the hair cells follows. The degeneration happens within a few weeks after a kitten’s birth. The resulting deafness is complete, with one or both ears affected.
“The pigment genes can also affect melanocytes in the iris, resulting in blue eyes in the absence of the normal pigment particles,” Dr. Strain says. “Thus, blue-eyed cats are more likely to be deaf than animals with normal colored irises.”
Some cats are deaf only in a single ear, known as unilateral deafness. Unilaterally deaf animals are difficult to identify by behavior, as they react to sound in much the same way that cats with complete hearing do, Dr. Strain says. If they are not identified as being deaf and they breed, they may to pass on their genetic disorder to offspring.
Unidentified Genes. The precise genes responsible for deafness in white cats have not yet been identified (remember, the W gene controls white skin and hair color). Consequently, there are no DNA tests available. “The only action that can reduce the possibility of deaf kittens is to have hearing testing done on both parents prior to breeding, since a unilaterally (or bilaterally) deaf parent will pass on the genetic defect,” Dr. Strain says. “Congenitally deaf cats should not be bred for this reason.”
While deafness can be inherited (as in most cases of deafness in white cats), most cases in non-white cats are likely acquired conditions. “Hereditary congenital deafness, if it is going to develop, should be present by five weeks of age,” Dr. Strain says. He notes that any cat can develop deafness later in life from non-genetic causes, not only white ones. They include:
- Aging (presbycusis)
- Noise-induced hearing loss
- Ototoxicity (drug or chemical-related damage to the inner ear), especially from the antibiotic gentamicin)
- Inner ear infection (otitis interna)
Owners may first suspect their pet’s deafness due to lack of response to everyday sounds. If you suspect that your cat is deaf — or losing his hearing — seek veterinary help.
The hearing test for pets, called BAER (brainstem auditory evoked response), is available at specialty veterinary practices and schools of veterinary medicine. A specialist performs the tests, which takes about 10 to 15 minutes. (See sidebar below.)
No treatment is available for inherited congenital deafness. However, veterinarians can be valuable allies in helping you and your cat cope with hearing loss. It’s sometimes simpler than you might think.
Unilaterally deaf animals tend to get along fine with hearing in only one ear. For bilaterally deaf cats, Drs. Strain and Collins recommend taking the following precautions:
- Keep bilaterally deaf cats indoors to avoid them getting hit by cars or being exposed to other physical dangers.
- Protect them from people. “Startled deaf animals can reflexively bite as a reflex, no matter how good-natured they otherwise are, so be especially careful with them around infants and toddlers,” Dr. Strain says.
“It may require extra time and patience on the owner’s part, but having a deaf animal is very doable,” Dr. Collins says. Deaf cats can make wonderful pets.
While studies of breed-specific prevalence are lacking, purebred cats that might be at risk for congenital deafness include:
White Scottish Fold
Norwegian Forest Cats
White Turkish Angora
White American Wirehair
White Cornish Rex
White American Shorthair
White Devon Rex
White British Shorthair
White Exotic Shorthair
White Oriental Shorthair
White Maine Coon
The BAER Hearing Test
The brainstem auditory evoked response (BAER) test performed by a neurologist can definitively diagnose deafness. During the 10- to 15-minute test, ear plugs or headphones placed over the cat’s head deliver clicks or tones to the ears. Small electrodes placed under the skin measure the electrical response in the brain to the tones by computer.
It’s rare for pets to show any evidence of pain from the placement of the electrodes, says George M. Strain, Ph.D., a researcher on deafness in pets and professor of neuroscience at Louisiana State University School of Veterinary Medicine. In most cases, he does not use sedation or anesthesia to perform BAER tests. “It is not necessary in order to obtain quality responses if patience and gentle handling are used,” he says. “The use of drugs adds unnecessary risk and expense.”
The BAER test is available at specialty veterinary practices and schools of veterinary medicine. A list of testing sites is available on Dr. Strain’s website:http://www.lsu.edu/deafness/baersite.htm