Splashed White 2 (SW2)
Gene or Region: PAX3
Reference Variant: C (N)
Mutant Variant: T (SW2)
Affected Breeds: Quarter 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: SW2/SW2 = homozygous for Splashed White 2, white markings expressed SW2/n = heterozygous for Splashed White 2, white markings possibly expressed n/n = no variant detected
General Description
Splashed White 2 (SW2) is found in Quarter Horses and can present as "normal" to "typical splashed white" markings.
SW2 Founder: Unknown
SW2 Phenotype: Heterozygous expressed as "normal" to typical splashed white markings; homozygous described as all white
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