Dominant White 39 (W39)
Gene or Region: KIT
Reference Variant: G
Mutant Variant: A
Affected Breeds: Stock-type Horse
Research Confidence: High - Mutations in KIT have been well-documented to cause white spotting in both the horse and other species
Explanation of Results: W39/W39 = homozygous for Dominant White 39, white markings expressed W39/n = heterozygous for Dominant White 39, white markings expressed n/n = no variant detected
General Description for Dominant White 39 (W39) "Penny"
Dominant White 39 (W39) "Penny" is currently found in Stock-type horses and may result in a nearly all white appearance with colored hairs mixed thoroughout the body and head.
W39 Discovered In: Oakbank Pretty As A Penny, Stock-type mare
W39 Phenotype: Nearly all white appearance with colored hairs mixed throughout body and head
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
Obradovic NA, McFadden A, Martin K, Vierra M, McLoone K, Martin E, Thomas A, Everts RE, Brooks SA, Lafayette C. "Three Novel KIT Polymorphisms Found in Horses with White Coat Color Phenotypes." (2025) Animals. 15(7), 915; 15(7), 915. https://www.mdpi.com/2076-2615/15/7/915.
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
Congenital Stationary Night Blindness & Leopard Complex
Congential Stationary Night Blindness (CSNB) is characterized by the inability to see well in low light and no-light situations. It is linked to Leopard Complex Spotting (LP), where homozygous horses (LP/LP) will have CSNB. Congential Stationary Night Blindness is present at birth and is non-progressive.
Champagne
Champagne (CH) is a dilution that affects all coat colors. Champagne foals are born with pink skin and blue eyes that slightly darken with age. Adult champagne horses have a distinct pumpkin colored skin with mottling in the hairless regions, as well as amber/green/tan eyes. Horses with multiple dilutions can be difficult to accurately identify color without genetic testing.