How blue eyes and deafness related in cats?

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 - 1.5 of total cat population Total number of cats with white coat and blue eyes account for - 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. 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. 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. #melanocytes #tapetumLucidum #Epistatic #CAT #AlbinoCats #OjosAzulesBreed #OjosAzules #mutations #Siamese #gene #deafness