Dominant white (W) and white spotting (ws) are coat traits controlled by the W locus of the KIT gene. The W allele produces a completely white coat with a single copy and may be associated with blue eyes and congenital deafness. The ws allele produces white patches of variable extent and additive effect: ws/ws homozygotes show more white than heterozygotes. It is a color trait, not a disease, but with health consequences (hearing) that the breeder must manage.

White spotting is common in breeds such as the Norwegian Forest Cat, Maine Coon or Sacred Birman (gloves); dominant white characterizes the white Turkish Angora and the Foreign White. According to classic studies, deafness would affect approximately 10-20% of white cats with golden eyes and more than half of white cats with both eyes blue (approximate figures and variable between studies).

- Completely white coat (W allele) that masks any underlying color
- Blue, odd or golden eyes
- White patches of variable extent (chest, gloves, socks, collar, belly) with ws
- Greater extent of white in ws/ws than in ws/N
- Congenital uni- or bilateral deafness, especially in white cats with blue eyes

The association between white coat, blue eyes and deafness has been known for more than a century and was studied experimentally in the mid-20th century, establishing that the risk of deafness increases with the number of blue eyes. In the 2010s molecular genetics resolved the locus with the identification of insertions in the KIT gene: one associated with dominant white and a different one with spotting. This allowed the development of tests that distinguish W, ws and the wild-type allele, useful for predicting white patterns in the offspring and managing the risk of deafness.

- Test breeding animals to know their genotype (W, ws or wild-type allele) and predict the white of the offspring.
- Screen the hearing of all white kittens with a BAER test before assigning them to breeding or sale as breeding animals.
- Mating two dominant whites is inadvisable: it increases the proportion of white kittens at risk of deafness.
- Do not breed with confirmed deaf white cats.
- Record the genotype: white masks the rest of the colors and, without a test, useful pedigree information is lost.

Deafness is due to a developmental cochlear degeneration; it is not progressive or painful and is confirmed with BAER from the first weeks of life. Do not confuse ws spotting with the glove pattern specific to the Sacred Birman or with the white of the Snowshoe. Deaf white cats can have a good quality of life indoors with visual cues and stable routines.

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3. Anderson H et al. (2024) A new Finnish flavor of feline coat coloration, 'salmiak', is associated with a 95-kb deletion downstream of the KIT gene. Anim Genet. PMID: 38721753
4. OMIA:000209-9685 (blanco dominante) y OMIA:001737-9685 (moteado blanco, KIT) en Felis catus.