Splashed White 8 (SW8)
Gene or Region: MITF
Reference Variant: -
Mutant Variant: chr16:21555811_21558139del
Affected Breeds: Thoroughbreds
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: SW8/SW8 = homozygous for Splashed White 8, white markings expressed SW8/n = heterozygous for Splashed White 8, white markings expressed n/n = no variant detected
General Description for Splashed White 8
The de novo mutation was first identified in Southern Phantom, a 2016 bay overo by Bodemeister (TB) and out of Out For Revenge (TB). While the research did not disclose his name due to confidentiality protocols, the horse's owner confirmed his participation in the study to the APHA. Southern Phantom displayed a bald face, blue eyes, tall stockings, and belly white markings similar to other splashed white patterns, yet he tested negative for the known Splashed White variants at the time. Both of his parents are solid bay Thoroughbreds with minimal white markings.
SW8 Phenotype
Heterozygous expressed as bald/white face, may present with deafness, and often white socks with body markings
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, deafness, and sterility.
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
Bellone, R. R., Tanaka, J., Esdaile, E., Sutton, R.B., Payette, F., Leduc, L., Till, B.J., Abdel-Ghaffar, A.K., Hammond, M., Magdesian, K.G. (2023). A de novo 2.3 kb structural variant in MITF explains a novel splashed white phenotype in a Thoroughbred family. Animal Genetics, 00, 1–11. doi: 10.1111/age.13352
More Horse Color Genetics
Congenital Stationary Night Blindness & Leopard Complex
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
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.