WHITE CATS, EYE COLOURS AND DEAFNESS



ALBINO OR JUST WHITE?

A true albino cat

The eyes are unpigmented and appear pink. The skin is pale pink. A true albino kitten, age 7 weeks, owned by Michelle R. McGaha. The eyes are unpigmented and appear pink. The skin is pale pink. The mother is a tortie Manx, the father is unknown. He is very light sensitive and will need sun-protection on his ears to guard against skin cancer (all white-eared cats have a risk of skin cancer if they sunbathe too much). Contrary to popular belief, white cats with blue, orange or green eyes are not albino. Albino cats, such as the one in this photo, have pink (unpigmented) or bluish-pink eyes and, like most albino animals, their eyes are sensitive to light. The white colour in cats is due to a gene that masks any other colour genes (this is why white cats can have non-white or bi-colour kittens). Albinism is a different mutation that causes the absence of colour, not the covering up of colour. When owners talk about having green-eyed or orange-eyed albino cats, they mean green-eyed or orange-eyed "dominant white" cats. In this context, dominant means a gene that masks other genes, it does not mean the cat has a dominant personality. Recessive white is an alternate name for the blue-eyed/pink-eyed albino gene which is part of the colourpoint series of genes. The white spotting gene can sometimes produced solid white cats and is also sometimes called recessive white. It is also a fallacy that "all blue-eyed white cats are born deaf". All kittens are born blue-eyed and with their ears folded down. Whether they will stay blue-eyed and whether they will be deaf can only be ascertained after a few weeks. Not all blue-eyed white cats will be deaf (as this article explains). DOMINANT WHITE Dominant white (more properly "epistatic white" since it occurs on a different gene to the black-based or red-based colours) denoted by the gene symbol WD (previously "W"), is the colour associated with deafness in cats. Dominant white masks all other colours and purebred dominant white cats may have blue, orange or odd eyes (randombred dominant white cats have a wider palette of colours). Those with blue eyes have a high chance of deafness. Those with one blue eye have a high chance of deafness on the blue-eyed side. Those with orange eyes are far less likely to be deaf. Some dominant white kittens are born with smudges of coloured fur on top of the head where the colour is incompletely masked, this smudge of colour usually disappears by adulthood, but kittens with colour smudges are more likely to have normal hearing. These cats are not albinos; genetically they can be any colour, but the white is dominant to those other colours (albinism is an absence of other colours).

Lacy has the dominant white gene associated with blue eyes and deafness (Lacy is deaf). Lacy owns Greg Schultz who refers to her as "The Queen". Mikey has the dominant white gene, but has green eyes rather than blue. He is also deaf. Mikey is owned by Jennifer Moore (ibjennyjenny).

In some animals, the blue-eyed white trait is sex-linked (carried on the X chromosome) and is found in males more often than in females. In cats, the gene for white is carried on an autosome (a chromosome other than the X or Y sex chromosomes) and the trait occurs equally in male and female cats. Blue-eyed white is not sex-linked in cats.

Readers may have noticed that there are dominant white cats with green, yellow or hazel eyes. In pedigree cats, only orange, odd or blue are accepted with dominant white. Orange eyes were selectively bred from the original mish-mash of eye colours back in the late 1800s when many white cats back had nondescript yellowish eyes. It may be easier to think of it in terms of orange = "pigmented" and blue = "non pigmented." Orange is just one colour in a continuous spectrum between green, yellow, orange and hazel. Random bred cats have a lot more variety in terms of pigment because they aren't bred to standardised colours through generations of selective breeding for the most intense coppery-orange possible. Cats with coloured and patterned coats can have all sorts of eye colours. Dominant white masks the coat colour, but does not always mask the eye colour (otherwise there would never be orange-eyed whites). So in random bred dominant white cats there is a much wider range of eye colours even though the fur is white. In the past, a variety known as the Russian Angora was a green-eyed dominant white variety.

WHITE SPOTTING

The gene for white spotting, denoted by the gene symbol "WS" (previously just "S"), can also create the impression of a self white cat. This gene is dominant and is variable in the way it is expressed - a cat may have a small amount of white or may be wholly white and all stages in between those two extremes. Unlike dominant white, white spotting is not linked to deafness. The lockets and buttons in solid cats are thought to be a wild variation of gene, and are not the "white spotting" gene.

Some white cats are due to the very variable expression of the gene for white spotting. The diagram above shows a typical progression from solid colour through to solid white caused by this gene. The number by each diagram is the "Grade" of spotting from Grade 0 (no white spotting) through to Grade 10 where white spotting has obscured all of the base colour. Grade 10 white spotted cats resemble solid white cats, but are rarely deaf. Again, small spots of colour may be discernible on cats that appear solid white due to the white spotting gene. ALBINO CATS (RECESSIVE WHITE) Albino is generally thought of as pure white, but the situation in cats is more complex. There are five known alleles for albinism: blue-eyed albino ("ca"), pink-eyed albino ("c"), Burmese pattern ("cb"), Siamese pattern ("cs")and full colour (non-albino, "C"). Full colour is dominant to all of the other four alleles. Burmese pattern is incompletely dominant to Siamese pattern; cats that inherit one of each of those genes will be intermediate in pattern and is known as Tonkinese. A quirk of the Siamese form of albinism is that it is temperature dependent with warm areas of the body being paler than cooler areas. For this reason, it is often described as "colour restriction" rather than albinism. Pink-eyed albino appears to be recessive to all of the other albino mutations. Albinism is not linked to deafness in cats ("dominant white" (W) is the gene linked to deafness). Full albinism - also known as recessive white - is rare. When present it affects the structure of the tapetum of the eye so tht it reflects red/pink instead of reflecting green. In 1927, judge Mrs Basnett reported on the Paris Cat Show held on 14th and 15th of January by the Cat Club de France and wrote "One lady brought for my inspection a Siamese Albino of about 4 months; I could not see a trace of any shading anywhere on the white coat, tail, legs, ears or mask; the eyes were a very beautiful blue, and their fiery centre seemed to be accentuated by the absence of all shading. In appearance it was a very typical Siamese with the long sleek body and whip tail, and a very beautiful wedge-shaped head and face." In “Siamese Les Races De Chats” 1935, Dr Phillip Jumaud wrote “Albinism may occur among the Siamese. Thus a participant CCF France, M. [Monsieur] Fircinai de Cholet recently reported a new case. The observation concerns a young Siamese cat aged 6 months which was all white with pale cream extremities, this cats eyes were red. This small size animal had a knotted tail. Mated many times this cat never reproduced.” Albino Siamese have also been purposely bred; they are completely white Siamese-type cats with bluish-pink eyes (true "pink eyes" are uncommon due to the physical structure of a cats' eyes). The "European Albino" bred in Belgium is a European shorthair type white cat with ruby-red eyes which have pale translucent blue irises. The albino cats reported in Europe and the USA seem to be intermediate between pink-eyed albino and blue-eyed albino. A true pink-eyed albino was reported in 1931 and again in 1980s in the USA. Albino Siamese had pinkish-blue eyes rather than the clear blue related to dominant white in the Foreign White breed. The mutation for "true albinism" was reported when a Chocolate Point female bred to her Chocolate Point son (this line became quite inbred in order to produce the albino cats). The recessive white gene has continued to lurk in the Chocolate and Cinnamon Oriental gene pool, where it somes manifests by affecting the eye structure and producing blue-eyed Orientals. When pink/red eye shine shows up in breeds of cat, or in randombreds, it is most likely due to chocolate or cinnamon in their ancestry. It has been observed in some oriental cats and in chocolate/cinnamon Devon Rex, Affected cats are not necessarily wholly or partly white and the only hint of this gene seems to be the red eye shine instead of green eye shine! Why does it only visibly affect eye structure? All multi-celled creatures are mosaics where genes can be switched on in some cells but not in others. For some reason, during the development of the embryo, the lurking albino gene got switched on in those cells that formed the eyes. OTHER ALBINISM An albino kitten was born at Chelmsford Cats Protection League shelter in the 1990s and required handrearing. It was described as white furred and having very pale pink ears, nose leather and paw pads though I have no information on its long term survival. Albino kittens have turned up more recently in the Bengal breed, unsurprising since albinism is found in the Asian Leopard Cat (the wild parent of the Bengal). In the Ojos Azules cat, normally typified by bright blue eyes in combination with colours other than white or colourpoint, the homozygous form of the gene has caused dead albino kittens.

WHITE CATS AND DEAFNESS

A few years back I was asked three related questions on a newsgroup. This article is adapted from my answer. - Are white cats, particularly blue eyed white cats, always deaf or is this an old wives' tale?

- Is deafness linked only to odd-eyed white cats?

- Some blue-eyed whites aren't deaf - why? There is an established link between the white coat color, blue eyes and deafness. The tapetum lucidum is generated from the same stem cells as melanocytes (pigment cells). The blue eyes in a piebald or epistatic white cat indicates a lack of tapetum. Deafness is caused by an absence of a cell layer in the inner ear that originates from the same stem cells as well. In odd-eyed white cats, the ear on the blue-eyed side may be deaf, but the one on the orange-eyed side usually has normal hearing. Not all blue-eyed whites will be deaf since there are several different genes causing the same physical attributes (whiteness, blue-eyedness) so it all depends on the cat's genotype (its genetic make-up) not its phenotype (its physical appearance). Some people claim that 99% of blue-eyed white cats are deaf. This is inaccurate because blue-eyedness and whiteness can both be caused by different genes. It all depends on what genes the cat has inherited. These are the actual figures from scientific studies around the world. The percentages are given in ranges because results are different in different areas, partly because of the different genes found in the cat population. Where a cat is classed as deaf, the deafness may affect one or both ears. 95% of the general cat population is non-white cats (i.e. not pure white) and congenital deafness is extremely rare in non-white cats.

5% of the general cat population is white cats (i.e. pure white). 15-40% of these pure white cats have one or two blue-eyes.

Of those white cats with one or two blue eyes, 60-80% are deaf; 20-40% have normal hearing; 30-40% had one blue eye and were deaf while 60-70% had one blue eye and normal hearing.

Of the 5% of white cats in the overall population, 60-80% had eyes of other colors (e.g. orange, green). Of those 10- 20% were deaf and 80-90% had normal hearing.

Deaf white cats with one or two blue eyes account for 0.25 - 1.5 of total cat population

Total number of cats with white coat and blue eyes account for 0.75 - 2.0% of total cat population It is evident from those studies that blue eyed whites exhibit a higher incidence of deafness than do orange/green eyed whites or non-white cats! But not all blue eyed whites are deaf and here's why:- There is a known link between white coat color, blue eyes and deafness - but since the coat and eye color can be caused by different genes it means that only some blue eyed whites are deaf. There is a gene/gene complex which causes white coat, blue eyes and deafness, but not all cats get their white coat and blue eyes from that particular gene, so not all white cats will be deaf. If the cat is a Foreign/Oriental White, it carries the gene for 'Siamese Blue Eyes' which is not linked to deafness (the gene for Siamese Blue Eyes is linked to cross-eyes instead). Siamese blue eyes have a reflective tapetum, but this is depigmented because the Siamese colour is caused by albinism. This depigmentation gives the red-eye with flash cameras. Random matings can mean that this gene sometimes appears in non Oriental-looking cats which have colorpoint cats in their ancestry.

Crystal (owned by Alana Harley, Vancouver Island, Canada) has two different types of blue eye. As this photo shows, one eye has normal green eye-shine and the other has pink eye shine. Depigmentation gives the red-eye with flash cameras

Albino cats are also white. True albinism causes pinkish eyes, but some albinos or partial albinos have pale blue eyes. There are too few albino cats studied to draw firm conclusions, but this mutation is not necessarily linked with deafness. It is also hard for a cat owner to determine whether their cat is a blue-eyed albino cat rather than an ordinary blue-eyed white.

Jamie Linton, who volunteers at a shelter in California, came across this blue-eyed white young cat. The blue is restricted to an inner ring around the pupil, fading to white around the outside of the iris. It wasn't known if the cat was deaf. The most likely explanation seems to be that pigment remained concentrated at either end of the iris muscles as the eye grew, rather than being distributed evenly - a bit like pulling toffee where the middle section goes pale as it it stretched and the more intense colour remains at either end.

There is also a gene for blue eyes which is inherited separately from coat color. This is the gene responsible for the Ojos Azules breed. If the cat is white colored, there is no easy way of telling whether it has the blue-eyed-deaf-ear type gene or the Ojos-Azules-blue-eyes type gene. It's only possible to tell that a cat has this particular gene if the cat is non-white and has blue eyes. Genes for blue eyes independent of coat color may be more common than previously realised. I have encountered three blue-eyed random-bred cats (one ginger, one silver tabby, one brown tabby) in one UK town between 1989 and 1995. This may be the same gene as Ojos Azules, or it may be due to different gene mutations. Other types of blue eye are being discovered in all-white cats in Asia, the blue is different than Siamese Blue Eyes, but does not seem to cause deafness.

The Lady Chablis, belonging to Denise Parmentier, is an odd-eyed white. One eye is yellow-green and the other is blue. She has perfect hearing. Odd-eyed white cat photographed by Rodrigo Arancibia in Iquique, Chile. She shows no sign of deafness. her kittens are solid white, indicating the dominant white gene.

The white coat can be caused either by a gene for white coloration or by a gene for 'white patching' - sometimes the white patching is so extensive that the cat appears solid white. If the white cat exhibited a few colored hairs or a smudge of color on its body (usually on the head) as a kitten, then it should have normal hearing even if it has blue eyes because it has inherited a non-deafness causing gene for white coat! However, blue-eyed bicolour cats occur and the more white they have in the region of their eyes and ears, the more likely they are to be deaf. This is because one of those genes for white affects the development of both the eyes and ears - it causes lack of eye pigmentation (i.e. blue eyes) and deafness - and since the eyes and ears are close together, if that gene affects that area of the body, it is likely to affect both sense organs (hence odd eyed whites may be deaf on the blue-eyed side).

Aries, a blue-eyed silver-tabby-and-white Norwegian Forest Cat bred by Raquel Ortega Cormenzana of MONTEGANCEDO*ES (Madrid). Sometimes bicolour cats with white faces have blue eyes. Aries has has perfect hearing because the white does not extend to the ears.

Congenital deafness can also be caused by a variety of hereditary factors, just as in humans. Due to random mutation or the wide gene pool, cats of any color can be born deaf (probably less than 1%) - including orange-eyed whites. Hence deaf white cats with non-blue eyes can occasionally appear and in these cases the deafness is not linked to coat color. Deafness can also be caused by illness or injury, so a person adopting a deaf cat may not know whether the cat was born that way or became deaf later on.

There are also green-eyed white cats, the Russian Angora is green-eyed and white is a favorite color. Green-eyed white cats have a lower incidence of deafness than blue-eyed white cats because the gene for white they carry does not normally affect their eye color. It is similar for orange eyed whites; they rarely have congenital deafness. Genetic expression is very variable and orange-eyed/odd-eyed/blue-eyed whites are interbred in many breeds - hence up to 20% of non-blue-eyed, white cats may have some degree of hearing impairment depending on what gene is causing them to have a white coat.

So overall, blue-eyed white cats stand a higher than usual chance of being deaf; but they are not guaranteed to be deaf. Odd-eyed white cats may be deaf on the blue-eyed side. If you have a deaf white cat, it is not advisable to breed from it as this would pass the trait along. Deaf white cats are banned from exhibition or breeding by some fancies in Europe and there is a move to reduce or eliminate this trait from British breeding lines of various breeds. Deafness can cause problems because a cat cannot hear danger approaching. It can cause problems to breeders because deaf female cats cannot hear their kittens crying out and may neglect them. Deaf kittens cannot hear their mother calling to them and may get lost. Deaf cats also seem to have no volume control when meowing. For more information see Living With a Deaf Cat.

CONSIDERATIONS FOR ALL BLUE-EYED BREEDS

There are various known and unknown genes involved in white spotting and in blue-eyes. In solid white and high white cats there is a link to deafness because melanin is involved in the development of the inner ear (the part that detects sound vibrations). BAER testing (acoustically evoked brain stem responses) is used by many European breeders to ensure that they don't deliberately breed deaf cats. The prevalence of deafness and partial hearing in an experimental colony of white cats was 67% (deaf - 0.55 coefficient of heritability) and 29% (partial hearing - 0.75 coefficient of heritability) which suggests a pleiotropic major gene (a gene that has 2 seemingly unrelated traits) and the likelihood of polygenes.

Geigy CA, Heid S, Steffen F, Danielson K, Jaggy A, Gaillard C (2007). "Does a pleiotropic gene explain deafness and blue irises in white cats?". Veterinary Journal. 173 (3): 548–553. PMID 16956778.

This was commented upon by Strain GM, in "Deafness in blue-eyed white cats: the uphill road to solving polygenic disorders."Vet J. 2007 May;173(3):471-2. Epub 2007 Feb 21.

NOTES 1. THE "ALBINO SIAMESE"

Feline geneticist Don Shaw, writing in Cats Magazine, September 1972 to February 1973, looked into the so-called Albino Siamese and wrote that not all so called Albino Siamese were true genetic albinos and that many are blue-eyed whites of Siamese type (what we now call Foreign Whites). However, some Albino Siamese had pinkish-blue eyes rather than the clear blue of other blue-eyed white breeds. His research found that early registrations of "Albino Siamese" mentioned "Chinese Whites" - reportedly cats of Asian origin with Malay type and apparently blue-eyed whites having the piebald (white spotting) gene. Unlike other albino animals, the cat's eye structure always gave bluish tone, even to the pink or ruby eyes normally associated with albino animals; this made true albinism in cats difficult to detect. A mutation for "true albinism" was reported when a Chocolate Point female bred to her Chocolate Point son. Most of the early breedings to produce these reported "Albino Siamese" were within the same Chocolate Point line, meaining the cats were relatively inbred. It had always been suggested that the mother/son mating resulted in doubling up of a recessive allele for albinism, however Shaw challenged this theory. A Chinese White, and thus white spotting, had been introduced into the Chocolate Point Siamese line and this Chinese White may have carried both white spotting and albinism. If so, the apparently true albinism in Albino Siamese would have been introduced from outside and not occurred as a mutation within the breed. Alternatively, he had noted that Chocolate Point and Lilac Point Siamese seemed to have a pink glow to their otherwise blue eye which wasn't seen in Seal Points or Blue Points. Shaw believed the supposed Albino Siamese were blue-eyed whites resulting from the white spotting inherited from the Chinese Whites PLUS the pinkish tone due to being homozygous Chocolate Point Siamese (this would be masked by the white spotting) - this combination mimicked true albino. Since the alleged Albino Siamese resulted from inbreeding Chocolate Point Siamese, so Shaw reasonably expected the offspring to have the same pinkish-blue eyes he had observed in Chocolate Points along with a double dose of white spotting that produced a wholly white coat. The possible alternatives presented by Shaw were that Albino Siamese might be true genetic albinos or they might simply be blue-eyed whites with pale blue, slightly pink-tinted, eye colour. He didn't have enough breeding data to determine which, but there was enough data to demonstrate the presence of white spotting genes in that line (white toes, lockets etc). Since Shaw’s time, true albinism has been seen in cats (the eyes being pink with only a slight blue tint). It has been recorded in the wild in the Asian Leopard Cat and also in the domestic descendants of Leopard Cat hybrids, the Bengal. Albinism has spread from the Siamese to closely related Oriental breeds. Greer Stothers sent me this report of an albino cat in 2013. Pangur is an oriental longhair with very pale skin and nose. Her paw-pads and ears, are pink-tinted white threaded through with red veins. Her eyes look like faded lilac-blue (Greer describes it as an Elizabeth Taylor colour) and when you look closer, you can see that the pupil is a dull red, while what looks like lilac is just the pale blue refraction of the lens overlaid on more red. You can very clearly see the blood vessels beneath the iris which can be a bit creepy, because when the light hits Pangur in the right way, her entire eye turns a muted pinkish red. In the dark, they reflect bright red. Pangur is an indoor cat, and has only been into the backyard under supervision. In direct sunlight, she's unable to open her eyes, and has to squint through little slits. She also squints when looking out of windows. She's very sensitive to light, and hates being photographed using flash. In contrast to her poor daytime vision, she can see very well in the right lighting. Her hearing has been tested by the vet and is perfect. Greer has checked Pangur’s pedigree and found inbreeding. Pangur has two grandmothers, but only one grandfather, which means her parents are half-siblings. It seems likely that the grandfather passed on his recessive albinism gene to Pangur’s parents, and Pangur inherited two copies of the gene. One of her sisters appears to be albino, but her other siblings have neon-bright cyan eyes (i.e. the blue colour normal for foreign white cats).

NOTES 2. OTHER BLUE-EYED CATS