Dominant White 23 (W23)
Gene or Region: KIT
Affected Breeds: Arabian
Research Confidence: High - Mutations in KIT have been well-documented to cause white spotting in both the horse and other species
Explanation of Results: W23/W23 = homozygous for Dominant White 23, white markings expressed W23/n = heterozygous for Dominant White 23, white markings expressed n/n = no variant detected
General Description for Dominant White 23 (W23)
Dominant White 23 (W23) is found in Arabians and may result in a near to full white coat.
W23 Founder: Boomori Simply Stunning, Arabian stallion
W23 Phenotype: Near to full white
Gene Information
W23 was founded in an Arabian stallion who had two foals that were full white, but currently the line and mutation is thought to be extinct, 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. The W23 variant was identified in the white Arabian stallion Boomori Simply Stunning, who produced two white offspring, Meadowview Ivory and Just a Dream. However, it appears that the W23 lineage has since died out.
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.
More Horse Color Genetics
Cream
Cream (CR) is a dilution that is characterized by diluting or lightening both black-based and red-based horses. A single CR allele lightens red pigment to Palomino but does not overtly affect Black pigment. Two CR alleles results in extreme dilution of the hair, skin, and eyes of any color, though black-based horses tend to retain more pigment than red-based horses.