Dominant White 2 (W2)
Gene or Region: KIT
Reference Variant: C (N)
Mutant Variant: T (W2)
Affected Breeds: Thoroughbred
Research Confidence: High - Mutations in KIT have been well-documented to cause white spotting in both the horse and other species
Explanation of Results: W2/W2 = homozygous for Dominant White, white markings expressed W2/n = heterozygous for Dominant White, white markings expressed n/n = no variant detected
General Description
Dominant White 2 (W2) is found in Thoroughbreds and may result in an extensive to completely white coat.
W2 Founder: Kentucky Colonel (born 1946)
W2 Phenotype: Extensive to Completely White
Gene Information
KIT is a tyrosine kinase receptor that is vital for normal development. Mutations in other species have led to white spotting, anemia, sterility, and certain types of tumors. However, no negative health effects associated with dominant white have ever been documented in the horse. The various W alleles encompass a variety of mutations, all resulting in changes to the encoded protein.
References
Haase B et al., “Allelic heterogeneity at the equine KIT locus in dominant white (W) horses.” (2007) PLoS Genet. 3: e195.
Haase B et al., “Seven novel KIT mutations in horses with white coat colour phenotypes.” (2009) Anim Genet. 40: 623-9.
Holl H et al., “De novo mutation of KIT discovered as a result of a non-hereditary white coat colour pattern.” (2010) Anim Genet. 41: 196-8.
Haase B et al., “Five novel KIT mutations in horses with white coat colour phenotypes.” (2011) Anim Genet. 42: 337-9.
Hauswirth R et al., “Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes.” (2013) Anim Genet. 44: 763-5.
Holl H et al., “A novel splice mutation within equine KIT and the W15 allele in the homozygous state lead to all white coat color phenotypes.” (2017) Anim Genet. DOI: 10.1111/age.12554
Durig N et al., “Whole genome sequencing reveals a novel deletion variant in the KIT gene in horses with white spotted coat colour phenotypes.” (2017) Anim Genet. In press.
Photo of FVF Kaliedescope, Courtesy of Fanny Patin, Fern Valley Farm
More Horse Color Genetics
Splashed White
Splashed Whites are white spotting patterns characterized by large white markings on the legs, face, and sometimes the tail/belly, giving a horse the appearance of being dipped in paint. Often, splashed white horses have blue or partially blue eyes, and may be deaf. On rare occasions, splashed white may be hidden.