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Gene or Region: MITF
Reference Variant: A
Mutant Variant: T
Affected Breeds: PRE
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: SW9/SW9 = homozygous for Splashed White 9, white markings expressed SW9/n = heterozygous for Splashed White 9, white markings expressed n/n = no variant detected
Splashed White 9 (SW9) / Giltor is found in Pura Raza Espanola horses and results in white markings that give the horse the appearance of being dipped in paint with the edges of the white often sharp.
SW9 Discovered In: Laurel GT
_SW9 Phenotype:_ White markings that give the horse the appearance of being dipped in paint with the edges of the white often sharp
MITF is a transcription factor that serves to activate several key genes involved in the development of pigmentation. Mutations in both the horse and in other species have led to white spotting, deafness, and sterility.
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
Incontinentia Pigmenti (IP) is a brindle-like appearance found only in female horses. Affected male embryos die during development in utero. Ip foals develop pruritic, exudative lesions soon after booth. The affected regions progress into wart-like lesions and areas of alopecia (hair loss), with occasional wooly hair re-growth. Affected horses display streaks of darker and lighter coat coloration from birth.
Lethal White Overo is a recessive trait characterized by patches of white bordered or “framed” by normal pigmentation. It is usually accompanied by blue eyes and generally white patterning does not cross the topline. Homozygous foals (LWO/LWO) are born completely white and with megacolon, an abnormal dilation of colon which necessitates immediate euthanasia.
