Splashed White 5 (SW5)
Gene or Region: MITF
Mutant Variant: - (SW5)
Affected Breeds: Quarter Horse & Paint Horse
Research Confidence: High - Mutations in MITF and PAX3 have been well-documented to cause white spotting in both the horse and other species, even humans!
Explanation of Results: SW5/SW5 = homozygous for Splashed White 5, not been described SW5/n = heterozygous for Splashed White 5, trait expressed n/n = no trait expressed
General Description
Splashed White 5 (SW5) is found in Quarter and Paint Horses, and may result in bald/white face and two blue eyes, often white socks with body markings and potentially deafness.
Phenotype: Bald / white face, blue eyes, often white socks, and a high incidence of deafness.
Gene Information
MITF is a transcription factor that serves to activate several key genes involved in the development of pigmentation.
References
McFadden, A., Martin, K., Foster, G., Vierra, M., Lundquist, E., Everts, R., Martin, E., Volz, E., McLoone, K., Brooks, S., Lafayette, C. (2023) Two Novel Variants in MITF and PAX3 Associated with Splashed White Phenotypes in Horses. Journal of Equine Veterinary Science, July 2023.
Patterson, et. al., "Non-frameshift deletion on MITF is associated with a novel splashed white spotting pattern in horses (Equus caballus)" (2022) Anim Genet. 2022 Jun 7. doi: 10.1111/age.13225
Henkel, et al., "Whole-genome sequencing reveals a large deletion in the MITF gene in horses with white spotted coat colour and increased risk of deafness" (2019) Anim Genet. 50: 172-4.
Hauswirth R et al., “Mutations in MITF and PAX3 cause "splashed white" and other white spotting phenotypes in horses.” (2012) PLoS Genet. 8: e1002653.
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.
Magdesian, KG et al., "A de novo MITF deletion explains a novel splashed white phenotype in an American Paint Horse." (2020) The American Genetic Association
Photo of TK Ollies After Shock, courtesy of Penny Kleinschmidt
More Horse Color Genetics
Dominant White 13
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.