Splashed White (Coat colour pattern Horse)
Horses with the splashed white gene have an irregular white pattern that is highly variable in expression.
Horses with one copy usually have a large white blaze and other irregular markings. Blue eyes, white coloured legs and occasional small patches on the belly region are also possible. These markings often cannot be clearly distinguished from other white markings by appearance.
Horses with two copies are mostly medicine hats (→ upper head region and back coloured, while face, belly and legs are white) or otherwise show a high amount of white.
There are four splashed white mutations, the most common being SW1.
Genetic Test SW1: available in Shop
- Irregular white pattern, quite may be variable in appearance.
- Horses usually have a wide blaze, often wider on the lower part of the face.
- Face-white may be associated with blue eyes, white stockings and small white areas on the belly.
- May enhance other patterns (e.g. Tobiano) → higher amount of white in the pattern.
- The most common Splashed White mutations are difficult to tell apart by looking: either genetic testing or (in Quarter horses) pedigree analysis are required.
- Combination of two different variants possible – SW1/SW2 and SW1/SW3 horses are known.
- Two of the known four variants (SW2 & SW3) are associated with deafness.
The Splashed White phenotype is caused by different mutations in two different genes. Genetic tests are available for the following variants:
SW1: Mutation in the MITF Core Promoter
Quarter Horses, Thoroughbreds, Trakehner, Icelandic Horses, Miniature Horses, Shetland Ponies and many others.
Test in Shop
SW2: Change of a single basepair in exon 2 of PAX3 gene.
Quarter Horses and Paint Horses (“Katie Gun”-Line)
SW3: Deletion in Exon 5 des MITF-Gens.
Quarter Horses and Paint Horses (“TD Kid”-Line)
SW4: Mutation in PAX3 gene.
Appaloosas (“I’za Last Jet”- Line)
SW2 and SW3 are believed to result in early abortion of homozygous foals since no homozygous genotypes has yet been recorded.
One more SW variant was identified in a single American Standardbred foal.
Genotype and Lab Report
Inheritance: incomplete autosomal-dominant
→ Incomplete means that horses with only one copy of the variant (n/SW) will show a less pronounced phenotype than horses with two copies of the variant (SW/SW).
n/n = No Splashed White mutation.
n/SW = One copy of the SW-variant
Highly variable pattern. Often only blaze and sockings and/or small spots on belly. Blue eyes possible.
SW/W = Two copies of the SW-variant
Increased amount of white in pattern. Variable appearance, sometimes with completely white coat or medicine hat, especially if combined with another white spotting mutation. Blue eyes possible.
Hauswirth, R., Jude, R., Haase, B., Bellone, R.R., Archer, S., Holl, H., Brooks, S.A., Tozaki, T., Penedo, M.C., Rieder, S., Leeb, T.: Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes. Anim Genet 44:763-5, 2013. Pubmed reference: 23659293. Doi: 10.1111/age.12057.
Hauswirth, R., Haase, B., Blatter, M., Brooks, S.A., Burger, D., Drögemüller, C., Gerber, V., Henke, D., Janda, J., Jude, R., Magdesian, K.G., Matthews, J.M., Poncet, P.A., Svansson, V., Tozaki, T., Wilkinson-White, L., Penedo, M.C., Rieder, S., Leeb, T.: Mutations in MITF and PAX3 cause „splashed white“ and other white spotting phenotypes in horses. PLoS Genet 8(4):e1002653, 2012. Pubmed reference: 22511888. Doi: 10.1371/journal.pgen.1002653.
Further information is available at Online Mendelian Inheritance in Animals for Splashed White 1&3 and Splashed White 2&4 verfügbar.