In 1868, Charles Darwin wrote in his work The variation of domesticated animals and plants: “if white cats have their eyes blue, they are almost always deaf”
Charles Darwin in 1868, in his work already anticipated that
white cats with blue eyes had a high probability
of being deaf. Photo: Wiki commons
Once again, the brilliant scientist was right since between 56% and 90% of cats (according to different studies) with white coat and blue eye color are deaf from one or both ears. And, if the white cat has a different eye color for each eye (heterochromia), it will be deaf on the side where it has the blue eye.
The root cause of this deafness must be found in the abscence of hair cells in the cochlea of these animals.
Left: detail of internal ear. Right: Hair cell in the cochlea.
Source: Wikicommons. Author Bruce Blaus
In the cochlea lies the sense of hearing of mammals. In deaf cats this structure lacks hair cells. Without them, the sounds don´t transform to electric signals that reach the brain to be interpreted, therefore the animal is deaf.
White cat with blue eyes. Very likely to be deaf.
Photo Pixabay
What is the relation between these cells and the cat’s eye color? The nexus seems to be found in the embryonic development. In this phase, there’s a structure (the neural tube) in which there are precursor cells called melanoblasts that migrate to the skin, eyes and ears. In the ear they are converted into hair cells like we mentioned previously. In the skin and eyes they should become melanocytes which determine the color of the hair. If that cellular migration is incomplete or incorrect the melanoblasts don’t reach the ear or the eye or the skin –or will arrive in insufficient quantities- so hairy cells won´t develop as they should and the animal will be deaf. The melanocytes won’t develop so the animal will be white and will have a clearer pigmentation –blue- for the eyes (the tonality of the eyes doesn’t only depend on the melanocytes).
Watch out, albino cats won’t have melanocytes in the skin or eyes (you’ll see the eyes as pinkish or red) and usually aren’t deaf since the lack of pigmentation is due to different reasons than the ones mentioned previously.
To know more:
- Hartwell Sarah, Beautiful bicolours– Tuxedo and magpie cats. messybeast.com/bicolours.htm
- García, Domingo. Genética del color de los gatos. Centro veterinario. JG. vetjg.com
- Broad, Michael. Calico cats. May 2012 www.pictures-of-cats.org/calico-cats.html
- La sordera en los gatos blancos. Todo sobre mi gato. 2013
http://www.todosobremigato.com/2013/10/la-sordera-en-los-gatos-blancos.html
- De la Nuez, D. ¿Por qué los gatos blancos de ojos azules suelen ser sordos?
- Ryugo, D.K et al. Feline deafness. Veterinary Clinics of North America: Small Animal Practice Volume 42, Issue 6, November 2012, Pages 1179–1207
- Kral, A. et al. Deaf white cats. Current biology. Volume 25, Issue 9, 4 May 2015, Pages R351–R353
- Strain, G. Deafness in blue-eyed white cats: The uphill road to solving polygenic disorders. The Veterinary Journal. Volume 173, Issue 3, May 2007, Pages 471–472