NO, not all pure white cats with blue eyes are deaf, however:
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:
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:
Wilson and Kane, 1959;
Bosher and Hallpike, 1965;
Bergsma and Brown, 1971;
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
12.1% were unilaterally deaf and 37.9% were
bilaterally deaf, or a total of 50% were affected.
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.