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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
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 (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.
