white spotting and epistatic white

White on cats is usually caused by one of two effects. White spotting causes varying amounts of white, anywhere from a tiny bit to full coverage. It has a distinct pattern - low amounts show up on the paws, chest, and muzzle, medium amounts generally cover the lower half of the cat, and the last colored spots will be on the tail and between the ears.

Epistatic white (also known as dominant white), on the other hand, makes the whole cat white, every time. Sometimes they may have a small smudge of color on their head when they are born, but this fades as they grow. It also has a known link to deafness, especially if the cat has blue eyes.

These were previously believed to be two separate genes, but a 2014 study found that they were both at the KIT locus. Mutations of the KIT gene are known to cause varying degrees of white and sometimes deafness in lots of different mammals. Both these alleles interfere with the survival of melanoblasts, which are precursors to the pigment-producing melanocytes. They may interfere with pigmentation in the eyes as well, making them blue, and in the case of dominant white, a lack of melanocytes in the inner ear can cause degeneration of those structures. There is no evidence at this point suggesting a link between white spotting and deafness.

The Birman gloving allele has also been found to be at the KIT locus. It is a recessive allele distinct to Birman cats that creates white paws. It is unclear how it interacts with the white spotting allele, if at all. The study with this finding has not been published, but it has been cited in many other papers in the last several years. I have been unable to track it down myself.

The genotypes are as follows:

Genotype Phenotype
WDWD Dominant white
WDWS Dominant white
WDw Dominant white
WSWS 50-100% white spotting
WSw 0-50% white spotting
ww No white
wwg No white
wgwg White gloves