Splashed White 1 (SW1)
Gene or Region: MITF
Reference Variant: T (N)
Mutant Variant: ATAATAACCTA (SW1)
Affected Breeds: Many
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: SW1/SW1 = homozygous for Splashed White 1, white markings expressed; possibly with blue eyes SW1/n = heterozygous for Splashed White 1, white markings expressed; possibly with blue eyes n/n = no variant detected
General Description for Splashed White 1
Splashed White 1 (SW1) is found in many breeds and presents as normal to larger white markings in a heterozygous horse and larger splashed white markings. possible bald face and blue eyes in a homozygous horse.
SW1 Discovered In: Unknown
SW1 Phenotype: Normal to large white markings, possible blue eyes in heterozygous horses; typical Splashed White markings and blue eyes in homozygous horses
Gene Information
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, blue eyes, deafness, and sterility. Current research evidence indicates Splashed White 1 is a mild variant resulting in color modification (depigmentation) with no reported/documented health anomilies or lethality as seen in other, more severe, Splashed White variants.
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