Splashed White 4 (SW4)
Gene or Region: PAX3
Reference Variant: G (N)
Mutant Variant: C (SW4)
Affected Breeds: Appaloosa
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: SW4/SW4 = SW4/SW4 = homozygous for Splashed White4, likely white markings expressed, UNOBSERVED SW4/n = heterozygous for Splashed White 4, trait expressed n/n = no trait expressed
General Description for Splashed White 3
Splashed White 4 (SW4) is found in Appaloosas, and may result in a broad blaze and partially blue eyes.
Phenotype: Typical splashed white (heterozygous)
Gene Information
_PAX3 _ is a transcription factor that is vital for normal development. Mutations in other species have led to white spotting, deafness, and alveolar rhabdomyosarcoma. In the horse, only deafness and white spotting have been reported.
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 Flashn My Assets, Courtesy of Julie Kreider.
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.