Dominant White 1 (W1)
Gene or Region: KIT
Reference Variant: C (N)
Mutant Variant: G (W1)
Affected Breeds: Franches-Montagnes
Research Confidence: High - Mutations in KIT have been well-documented to cause white spotting in both the horse and other species
Explanation of Results: W1/W1 = homozygous for Dominant White 1, white markings expressed W1/n = heterozygous for Dominant White 1, white markings expressed n/n = no variant detected
General Description for Dominant White 1
Dominant White 1 (W1) is found in Franches-Montagnes horses and may result in a mostly white coat.
W1 Founder: Cigale (born 1957)
W1 Phenotype: Mostly white, may be born with pigmentation along the topline that is lost with age
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
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
Dominant White 19
Dominant White 19 (W19) is found in Arabian horses and may result in a bald face with extended white on legs and belly spots for heterozygotes (W19/n). Homozygotes are reported to be nearly completely white with varying degrees of congenital birth defects and it is estimated that combinations of W19/W19 and other W19/X combinations may be largely lethal.