General Description for Dominant White 25 (W25)

Dominant White 25 (W25) is found in Australian Thoroughbreds and may result in a near to full white coat.

W25 Founder: Laughyoumay, Australian Thoroughbred mare W25 Phenotype: Near to full white, possibly with blue eyes

Gene Information

The W25 variant is a missense mutation located on exon 4 of the KIT gene that produces a partial to completely white coat pattern. It is believed to have originated with the Australian Thoroughbred mare Laughyoumay, born in 2001. Laughyoumay has produced at least two white colts, both bred by Winning Colours Farm. The eldest, Luna Park, carries Lethal White Overo (LOW) alongside W25 and is characterized by blue eyes and a completely white coat. The younger colt, Great Caesar Ghost, is a medicine hat—white with color only on and around his ears. W25 horses can exhibit a range of striking coat patterns, and we look forward to seeing more colorful W25 horses in the future. To date, no horses have been identified carrying two copies of W25.

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.