General Description for Dominant White 27 (W27)

W27 Founder: Milady Fair, Australian Thoroughbred mare W27 Phenotype: Partial to full white

Gene Information

The W27 variant is a missense mutation of the KIT gene that produces a partial to completely white coat pattern. It is thought to have originated with the Australian Thoroughbred mare Milady Fair, born in 1960. Milady Fair produced a white filly named Glacial, who in turn had a white colt named Khaleben. Khaleben sired three more white offspring, the most prolific of which was Colorful Gambler. Most horses carrying this mutation trace back to her great-grand-colt, Colorful Gambler, known for his extensive sabino-like pattern. Through his descendants, W27 spread into show jumpers and the Paint breed, in addition to Thoroughbreds. W27 horses that are not completely white often display striking spotted patterns.

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. Negative health effects associated with dominant white have not been documented in the horse, although some horse owners have reported health issues in some homozygotes of certain Ws while some Ws are homozygous lethal. 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.