Deafness in cats

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Literature

If you want to understand, how deafness affects your cat, you should know about the function and the anatomy of the cat's ears .

 

Please note, that mostly the literature about deafness in cats is in English.
 

Congenital Deafness and Its Recognition, George M. Strain, Ph.D. (English) 
 
Dalmat-Web, article about deafness (German) 
 
Deafness in Dogs &Cats, George M. Strain (Englisch) 
 
Heridity of predisposition for deafness and eye color in white cats, Caroline Geigy (German) 
 
List of articles dealing with deafness in cats 
 
Pigment Parade, Lorraine Shelton 
 
The 1995 All Breed White Deafness Survey, David Brinicombe (English) 
 
Tufts' Canine & Feline Breeding and Genetics Conference 2003 (English) 
 
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Deafness in cats

Short description

There are different kinds of deafness in cats, which can be classified according to the following criteria:

Occurence
Origin
Type
congenital
later on
inherited
acquired
conductive
sensorineural

The occurrence may be:

  • already when born  or shortly after birth (congenital),
  • or it may come later on (when getting old).

The origin of deafness may be:

  • based on genetic predisposition of the cat, that means it may be inherited,
  • or deafness may acquired due to an inflammation, an accident, etc.

The type of deafness in cats can be:

  • Conductive, i.e. the the sound transmission to the cochlea is blocked, because the ear canal or the middle ear cavity are closed, for example due to an inflammation in the middle ear or because of excessive production of cerumen.
  • Sensorineural because of the loss of the hair cells in the cochlea.

Deafness in white cats is congenital, inherited and sensorineural.

scheme of the ear
Scheme of the ear
 
Organ of Corti
Shown above: The Organ of Corti with the hair cells, which is in the Cochlea.
The Cochlea consists of three canals: Scala vestibuli, Scala media (= cochlear duct) and Scala tympani. Scala media is filled with Endolymph, a K+-ions fluid produced by the Stria vascularis.

At the outer edge of the Cochlea ganglions (Scala media) there is the so called Stria vascularis, which produces the endolymph containing K+-ions. Those ions are necessary that the hair cells in the Organ of Corti can function properly and can transmit the sound.
In congenital inherited deafness in cats the Stria is degenerated, which causes the degeneration of the hair cells, and thus the loss of hearing ability. Researches of the stria vascularis have shown, that the melanocytes (pigment cells) are missing and that the development of the melanocytes in white cats is suppressed shortly after birth. The ability to hear develops up to the 3rd week, and already starting with 3-4 weeks after birth a rapid loss of the hair cells begins which leads to deafness.

Deafness in white cats is likely to appear in connection with blue eyes. But also odd-eyed cats may be deaf, they are deaf on that ear, where the blue eye is located.
Cats may have defective hearing or may be deaf at all, deafness can also occur only in one ear.
The researches of G. Strain with 256 cats have proved, that 12% of white cats were unilateral deaf, and 38% of white cats were bilateral deaf, which gives a total of 50%: in white cats without blues eyes deafness occurred in 17% of the cats, in cats with one blue eye deafness occurred in 40% of the cats, and in cats with two blue eyes deafness occurred in 85% of the cats. Please see also in the chapter Literature in the left box.

Not all white cats with blue eyes are deaf, but the percentage of deaf cats is rather high.
It could be noticed a difference in white cats, whose blue eyes are the result of the Siamese-gene. Please read the article of Lorraine Shelton in the chapter Literature in the left box.

Genetics of deafness in cats

Inherited deafness in cats in conjunction with the pigment cells is already known since the 19th century. It was detected in 1828, and Charles Darwin commented on it.
Also breeding with hearing parent-animals might produce deaf kittens, as also breeding with deaf parents might result in hearing kittens.
Homozygous white cats are more likely to get blue eyes, and thus the probability of deafness is increased. The probability is much higher the more white cats with blue eyes are involved through the generations. Homozygous white cats with blue eyes originating from the Siamese-gene and being also homozygous for the Siamese-gene (cs) are less prone to deafness.

The mechanism of heredity is still not investigated completely.

Colors, which are more likely to produce deaf cats

All white cats of all breeds, where the white is based on the gene W:

  • Especially when having blue eyes.
  • Also when being odd-eyed, i.e. only one eye is blue.
    Deafness is mostly unilateral on that side, where the blue eye is located.

When reading the article of Lorraine Shelton (see the Literature in the left box), also cats with an extreme high amount of white might be affected by deafness (the white based on the piebald spotting gene S, mostly the homozygous cats having SS are affected), those are cats with the Van-pattern:

  • Especially when having blue eyes.
  • Also when being odd-eyed, i.e. only one eye is blue.
    Deafness is mostly unilateral on that side, where the blue eye is located.

Test methods for deafness in cats

Inspection, if a cat is deaf, is made by the shortly called audiometric test. Correctly spoken the test method is called BAER-test (brain stem auditory evoked response), also known as BEAP (brain stem auditory evoked potential) or as ABR (auditory brain stem response).
Similar to the EKG electric activities in the cochlea and in the brain are measured. The curves show several characteristic peaks, the first peak comes from the cochlea and the auditory nerve, all other peaks are coming from the brain.
In deaf animals the curve is almost flat.
Normally hearing cat
Deaf cat

Measurement is done separately for each ear.
Also unilateral deafness is genetically the same as bilateral deafness, it is only a different expression of deafness.
Measurement is done with tiny needle-electrodes, one electrode is placed on top of the head, one in front of the ear, and the mass-electrode is mostly placed on the neck. Those electrodes are connected with a computer specially equipped for such measurements. Due to the fact that the amplitudes of the curves are very small, the measurement is frequently repeated and an average of the amplitudes is calculated.
There are placed headphones on the ears of the cat, which are well padded, and an air-transmitted stimulus-click is presented periodically to the cat.
The entire procedure, separately performed for each ear, is finished within 10-15 minutes. The needle-electrodes are so tiny (smaller and thinner than the needles used for acupuncture) that the cat does not feel any pain. It is also not necessary to give an anesthesia to the cat, when the animal is relaxed and is not extremely frightened. Many veterinarians still give a short anesthesia to the cats, because they think it is more comfortable for themselves or because they are so used to it, but in fact an anesthesia is not necessary.

Consequences for breeding cats

In many organizations it is not permitted to cross two white cats. That might contribute to the reduction of the number of deaf white cats, but that is still not validated through scientific long-term researches and serious statistical data.

Another possibility might be to forbid blue eyes in cats. But such an action is disputable and questionable, because still cat with odd-eyes might be produced by parents having orange eyes. Also animals having orange eyes might be deaf, even thought the occurrence of deafness is less.

Another alternative is to forbid white cats in general. That is also questionable and one gets reminded to times which should be left behind us. White animals occur by nature in all species. Is it the idea to forbid in general white animals or to distinguish them? In white tigers, having become famous by luck because of the two magicians Siegfried and Roy, where distinct breeding programs are developed to save them from being distinguished, we want to have white animals, but in cats not? Such a short-sighted thinking is very inconsequent and illogical.

Another, but extreme alternative could be to breed homozygous hearing white cats, whose eyes are the result of the Siamese-gene and which are homozygous for the Siamese-gene, because in those white cats the probability of being deaf is much less.

There are performed many researches concerning mainly dogs, but scientific long-term researches and studies in cats with serious statistical data are unfortunately not on the way.
Thus one must wait until it is clarified, how the heredity of deafness in cats is working.

 
 

 
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