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white cats and deafness

Dominant white
Dominant white (more correct is “episiotomy” white since it can be found on a different gene on the black-based or red-based colors) is the color linked to deafness with cats. Dominant white masks all other colors and the cats can have blue, orange or dissimilar eyes. Cats with blue eyes have a big chance to become deaf. Cats with one blue eye have a big chance to become deaf on the blue-eye side. Cats with orange eyes will probably be less deaf. Some dominant white kittens are born with a tuft of colored hair on top of the head, this usually disappears when they grow older, but these kittens have a bigger chance on a normal hearing.

White spots
The gene for white spots can lead to the impression of a complete white cat. This gene is semi-dominant and has different symptoms: a cat can have no visible white spots or can be completely white or all stadiums in between. In contrast with the dominant white type, white spots aren’t linked to deafness.
The fur color of some white cats can be attributed to the very variable expression of the gene which causes the white spots. The diagram shows the different forms from completely colored until completely white, which this gene causes. The number of each diagram is the “order” in which spots occur starting from order 0 (no white spots) until order 10: the white spots have removed each basis color. Order 10, cats with white spots, resemble dominant white cats, but they are seldom deaf. You might also see small colored spots on cats which seem dominant white because of the white spot gene.
Albino cats
In general people think that albino means pure white, but with cats the situation is much more complex. There are 5 known “alleles” * for albinism: blue-eye albino, pink-eye albino, Burman pattern, Siamese pattern and complete color (not-albino). The complete color is dominant to each of the other 4 alleles. The Burman pattern is incompletely dominant to the Siamese pattern; cats which will inherit one of each of the genes will have a deviating color which is called "tonkenise". A whim of the Siamese albinism form is that the form depends on the temperature: warm parts of the body are paler than the cooler areas. For this reason this is often described as “color restriction” rather than albinism. The pink-eye albino appears to be recessive to each of the other albino changes.
*alleles: One of a pair of genes which causes the different expression of a certain hereditary quality.
In 1927, during the cat exhibition in Paris on 14th and 15th January organized by “Cat Club de France", the jury member Mrs. Basnett reported the following: “I inspected a Siamese albino of about 4 months old. I couldn’t find a shadow trace on the white fur, tail, paws and ears; the eyes had a very nice blue color. It looked like a typical Siamese with the corresponding long slim body, wagging tail and a very nice wedge-shaped face and head"
More recently a Siamese albino has been bred, although time will tell if it will be made a permanent breed. It is a fully white cat (Siamese type) with blue-pink eyes (real “pink” eyes are rare, this can be attributed to the cat’s eye structure). The “European Albino” which is bred in Belgium, is an European short-haired white cat with ruby-red eyes with pale, transparent blue irises. The albino cats which have been reported in Europe and US appear to be between the pink-eye and the blue-eye albino. A real pink-eye albino was reported in 1931 and again in the eighties in the US.
The Ojos Azules, which is characterized by blue eyes in combination with colors others than white or colourpoint. The homozygotic form of the gene appears to cause dead albino cats.
*homozygotic: The concerning animal has stabile hereditary qualities. 
In the nineties an albino cat was born and raised in a cat-centre in Chelmsford (England). He was described as follows: White fur and very pale pink ears, nose and soles.  More recently albino cats have appeared in the Bengal breed, which is not surprising since albinism originally comes from the Asian Leopard cat (the wilder parent of the Bengal breed).
WHITE CATS AND DEAFNESS
Some frequently asked questions:
- Are white cats, especially blue-eye white cats, always deaf or is this an idle gossip?
- Is deafness only linked to white cats with dissimilar eyes? 
- Some blue eye cats aren’t deaf, why?
There is a connection between the white fur color, blue eyes and deafness. Deafness is linked to the gene for blue eyes and not to the gene for dissimilar eyes. Not all blue-eye white cats are deaf since there are more, different genes which cause the same physical qualities (paleness, blue eyes). It therefore all depends on the cat’s genotype (his genetical structure) and not on the cat’s phenotype (his physical appearance).
Some people claim that 99% of the blue-eye white cats are deaf. This isn’t right since blue eyes and a white fur can both be caused by different genes. It all depends on which genes the cat has inherited. These are the real figures of world-wide scientific studies. The percentages are given in circles since the results aren’t equal on different areas, partly due to the different genes which are found in the cat population. A cat is classified as being deaf; the deafness can influence one or both ears however.
95% of the general cat population doesn’t consist of white cats (not pure white) and inherent deafness is extremely rare with these cats.
5% of the general cat-population consists of white cats (pure white). 15-40% of these pure white cats have one or two blue eyes.
60-80% of the cats with one or two blue eyes are deaf; 20-40% has a normal hearing, 30-40% has one blue eye and is deaf although 60-70% has one blue eye and a normal hearing.
60-80% of the 5% white cats in the general cat population have another eye color (for example green, orange). 10-20% of this group is deaf and 80-90% of this group has a normal hearing.
The deaf white cats with one or two blue eyes represent 0,25 - 1,5 of the total cat population.
The total number of cats with a white fur and blue eyes represents 0,75 - 2,0% of the total cat population.
Studies clearly show that deafness occurs more often with blue-eye white cats than with orange/green-eye white or not white cats! But not all blue-eye white cats are deaf because of the following: There is a connection between the white fur color, blue eyes and deafness – but since the fur color and eye color can be caused by different genes this means that only some blue-eye white cats are deaf. There is a gene complex which causes the white fur and blue eyes, it is linked to deafness, but not all cats will get a white fur and blue eyes from this particular gene.
These cats have a reflecting membrane in the eye (green eyes with flash-photography) which distinguishes them from cats with the Siamese blue eye. If it concerns a cat from a Foreign/Oriental White, it will have the gene for “Siamese Blue Eyes” which is not linked to deafness (the gene for Siamese Blue Eyes is instead linked to “crossing eyes”). Siamese blue eyes don’t have a reflecting membrane and have red eyes with flash-cameras. Arbitrary mating can lead to it that this gene sometimes appears in cats which don’t look oriental and which have colorpoint cats in their ancestry.
Albino cats are also white. Real albinism causes pink eyes, but some albino’s or partly albino’s have pale blue eyes. Too few albino cats have been studied in order to be able to draw conclusions, but this mutation isn’t necessarily linked to deafness. For a cat-owner it is hard to determine if his cat is either a blue-eye albino cat or rather a blue-eye white cat.
There is also a gene for blue eyes which is inherited separated from the fur color. This is the gene which is responsible for the Ojos Azules breed. If the cat is white, it is hard to tell if it concerns the blue-eye-deaf-type gene or the ojos-azules-blue-eye gene. You can only tell that a cat has this specific gene if the cat isn’t white and has blue eyes. The genes for blue eyes independent of the fur color can occur much more general than people assumed until now. Other types of blue-eye cats are discovered with cats in Asia which are fully white, the blue of their eyes is different than the Siamese blue eyes, but doesn’t appear to cause deafness.
The white fur can be caused by a gene for a white coloring or by a gene for white spots. These white spots might cause that the cat appears to be completely white. If the white kitten has a couple of colored hairs or a colored spot on his body (usually on his head), he should have a normal hearing, even if he has blue eyes, since he has inherited a gene for his white fur which doesn’t cause deafness. Nevertheless, blue-eye cats which are bicoulored occur and the more white they have around their eyes and ears the more probable they are deaf. This is caused by the fact that one of the genes for the development of a white fur both influences the eyes and the ears (it causes a lack of eye pigmentation (blue eyes) and deafness) and since the eyes and ears can be found close to each other the gene which influences that part of the body will probably influence both senses. (Because of this cats with dissimilar eyes can be deaf on the blue-eye side).
Inherent deafness can be caused by several hereditary factors, just like with people. Due to arbitrary mutation or due to the large variety of genes which exist, cats (independent of the color they have) can be born deaf (probably less than 1%) – including orange-eye cats. That is why deafness with cats without blue eyes occurs now and then and in these cases the deafness is not linked to the fur color. Deafness can also be caused by illness or injuries, so that a person who adopts a deaf cat doesn’t know if the cat was born this way or if he became deaf later on.
There are also green-eye cats, the Russian Angora has green eyes and white is a favorite color. Green-eye white cats have a smaller chance to become deaf than blue-eye white cats since the gene for white which they have normally doesn’t influence their eye color. The same goes for orange-eye white cats; they seldom have inherited deafness. The extent in which genetical qualities are externally visible in cells is very variable and orange-eye/dissimilar-eye and blue-eye white cats are crossed between themselves in many breeds. That is why until 20% of the white cats without blue eyes might have some kind of hearing damage, depending on which gene caused the white fur color.
So, in general blue-eye white cats have a larger chance to become deaf than other cats, but it isn’t guaranteed that they are deaf. White cats with dissimilar eyes can be deaf on the blue-eye side. If you have a deaf white cat, we advise you to not make a nest since she will pass the deafness. Deaf white cats are forbidden on exhibitions and some movements in Europe don’t allow breeding. There is a tendency to reduce or eliminate this property by breeders of different breeds. Deafness can cause problems since a cat cannot hear approaching danger. It might cause problems for breeders since the deaf female cats cannot hear their kittens screaming and they therefore might get lost.
Remark: Not all blue-eye cats are white; also not all blue-eye not white cats are Ojos Azules. Blue eyes occur surprisingly often in arbitrary bred cats. Amongst others: the female wild silver tabby, black-white tomcats, red tabby tomcats (with white chest), long-haired red tabby tomcats.