Are all white cats with blue eyes deaf?

Question

I was told that all pure white cats with both eyes being blue are completely deaf, and that all pure white cats with one blue eye are deaf on the side that has the blue eye.

If the cat has even a single spot on it it is not considered pure white.

Google presents me with contradictory answers to this question.

It's partially brought up in the 1869 edition of Origin of Species Chapter 1 (earlier versions omits cat color):

Breeders believe that long limbs are almost always accompanied by an elongated head. Some instances of correlation are quite whimsical; thus cats which are entirely white and have blue eyes are generally deaf; but it has been lately stated by Mr. Tait that this is confined to the males. Colour and constitutional peculiarities go together, of which many remarkable cases could be given among animals and plants.

Answer 1

NO, not all pure white cats with blue eyes are deaf, however:

From FabCats:

In cats, congenital deafness is seen almost exclusively in white coated individuals.

The deafness is caused by degeneration of the auditory apparatus of the inner ear and may affect one ear (unilateral) or both (bilateral).

Breeding studies have defined the relationship between deafness in white cats and blue eye colour.

The gene responsible is autosomally dominant gene W with complete penetrance for white coat colour, with incomplete penetrance for deafness and incomplete dominance for blue iris colour. The variable penetrance of deafness and eye colour may be caused by interplay with other genes or environmental factors.

Cumulative studies from various countries have found:

References:

• Delack J B (1984) Hereditary deafness in the white cat. Compendium on continuing Education for the practising Veterinarian 6, 609–617

• Heid S, Hartmann R, Klinke R. (1998) A model for prelingual deafness, the congenitally deaf white cat - population statistics and degenerative changes, Hearing Research 115:101-112

• Bergsma, D.R & Brown, K.S (1971) White fur, blue eyes and deafness in the domestic cat, Journal of Heredity 62:171-18

• Strain GM. Deafness in blue-eyed white cats: the uphill road to solving polygenic disorders. Vet J. 2007;173(3):471-2. doi:10.1016/j.tvjl.2006.01.015

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From Deafness in blue-eyed white cats (by George M. Strain, Louisiana State University):

[Pure white cats with blue eyes] are well-known to be commonly affected by a congenital hereditary deafness that may affect one or both ears; the deafness is linked to the so-called W gene.

Reports of this condition date back to at least the 1930s (Bamber, 1933), and many investigators have studied it in subsequent years:

• Wolff, 1942;

• Wilson and Kane, 1959;

• Bosher and Hallpike, 1965;

• Bergsma and Brown, 1971;

• Mair, 1973;

• Mair and Elverland, 1977;

• Pujol et al., 1977;

• Rebillard et al., 1981a,b;

• Saada et al., 1996;

• Ryugo et al., 1998, 2003).

[...]

Delack (1984)¹⁾ analyzed three studies of deafness in nonpure breed white cats that included a total of 256 cats (Bosher and Hallpike, 1965; Mair, 1973; Bergsma and Brown, 1971);

• 12.1% were unilaterally deaf and 37.9% were bilaterally deaf, or a total of 50% were affected.

• When cats that were the offspring of two white parents were examined, the prevalence of deafness (unilateral or bilateral) ranged from 52% to 96%.

^{1) Delack, J.B., 1984. Hereditary deafness in the white cat. Compendium on Continuing Education for the Practicing Veterinarian 6, 609–619}

Two of the studies (Mair, 1973; Bergsma and Brown, 1971) examined the effect of blue eye colour on deafness, finding (respectively) a prevalence of deafness (unilateral and bilateral combined)

• of 85 and 64.9% in cats with two blue eyes,

• 40 and 39.1% in cats with one blue eye,

• and 16.7 and 22% in cats with no blue eyes.

So, not all white cats are deaf and not all blue-eyed white cats are deaf, but a great many of them are so-affected.

More:

• Cornell University - Ask Elizabeth: White Cats and Blindness/Deafness
• Gallaudet University - Cat breeds with tendency to hereditary deafness
• ABC Science - Deaf cats draw a blanc