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Gene or Region: KIT
Reference Variant: A
Mutant Variant: C
Affected Breeds: Many
Research Confidence: High - Mutations in KIT have been well-documented to cause white spotting in both the horse and other species
Explanation of Results: W35/W35 = homozygous for Dominant White 35, white markings expressed W35/n = heterozygous for Dominant White 35, white markings expressed n/n = no variant detected
Dominant White 35 (W35) is found in many breeds and may result in white markings on the face, legs, and back.
W35 Discovered in: A Sudden Holiday
W35 Phenotype: White markings on the face, legs, and back.
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.
_ McFadden, Aiden and Martin, Katie and Foster, Gabriel and Vierra, Micaela and Lundquist, Erica W. and Everts, Robin E. and Martin, Erik and Volz, Erin and McLoone, Kaitlyn and Brooks, Samantha A. and Lafayette, Christa, 5’Utr Variant in Kit Associated with White Spotting in Horses. http://dx.doi.org/10.2139/ssrn.4392246 _
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 A Sudden Holiday, courtesy of Branson Buckalew, Buckalew Show Horses
Dominant White 13 (W13) is found in Quarter Horse / American White Horse and may result in a completely white coat. This variant was originally described in a Quarter Horse / Peruvian Paso cross, and was assumed to have originated from the Quarter Horse side. However, we have observed W13 in the offspring of an American White Horse without known Quarter Horse ancestry.
