page_title: Splashed white
section_title: Inheritance and prevalence
hierarchical_section_title: Splashed white / Inheritance and prevalence
caption_attribution_description: Français&#160;: Jument de race bretonne de robe Splash White Overo (SW-1)
context_page_description: Splashed white or splash is a horse coat color pattern in the "overo" family of spotting patterns that produces pink-skinned, white markings. Many splashed whites have very modest markings, while others have the distinctive "dipped in white paint" pattern. Blue eyes are a hallmark of the pattern, and splash may account for otherwise "solid" blue-eyed horses. Splashed white occurs in a variety of geographically divergent breeds, from Morgans in North America to Kathiawari horses in India. The splashed white pattern is also associated with congenital deafness, though most splashed whites have normal hearing. Splashed white can be caused by multiple variants across two different genes, for which genetic testing is available.
context_section_description: DNA tests exist for six forms of splashed white across two different genes. SW-1, SW-3, SW-5, and SW-6 are mutations of MITF, while SW-2 and SW-4 are mutations of PAX3. SW-1 is thought have originated hundreds of years ago and today has been identified in the American Quarter Horse, American Paint Horse, Icelandic horse, Miniature horse, Morgan horse, Shetland pony and Trakehner.  SW-2 has been mainly found in and SW-3 has been exclusively found in certain lines of Quarter horses and Paints, with SW-3 being particularly rare. SW-2 has also been found in a few Noriker and Lipizzan horses. Another allele of splash informally called "Macchiato", produced by the gene MITF:p.N310S, has only been found in a single Franche-Montagne horse, probably a spontaneous mutation, and that individual was sterile. Splashed white 6 is thought to originate with a dual registered Paint horse and Quarter horse stallion.
  The splashed white phenotype can be caused by mutations to either MITF or PAX3. SW-1 is the MITFᵖʳᵒᵐ¹ mutation, the most prevalent. It appears to be several hundred years old and predates the development of modern breeds.  SW-2 is a PAX3 mutation (PAX3C70Y) once thought to be traced to a single Quarter Horse mare foaled in 1987, however it appears to actually have originated earlier and has been found in other breeds. SW-3, the MITFC280Sfs*20 mutation, has been seen in Quarter Horses but is very rare. Some horses of Quarter Horse lineage carry more than one splash mutation.
  The splashed white pattern was first studied in Finnish Drafts and Welsh ponies by Klemola in 1933. Klemola's multiple studies on the topic have since been largely discredited, his text describing to detail a pattern now recognised as sabino, and his illustrations featuring horses that according to modern knowledge would be a mixture of splashed whites, tobianos, sabinos, and combinations of multiple spotting factors. Originally believed to be very rare outside of Europe, splash is turning out to be more common than previously thought, possibly due to the pattern's tendency to masquerade as modest markings. For example, minimally marked splashed whites have been responsible for cropouts among American Quarter Horses.
  Since the original study, SW-1 has been confirmed in the Finnhorse by genetic testing. In addition to breeds identified as carrying the SW-1, -2 or -3 alleles, color patterns described as splashed white but not yet verified via genetic testing have also been identified in American Saddlebreds, Shire horse, Clydesdales, and the Irish Tinker or Gypsy horse.
  There may be additional forms not yet mapped.  However studies suggest that it is not part of the linkage group that includes roan and tobiano. The KIT gene is not thought to be a candidate gene for splashed white. Preliminary studies from the early part of the 20th century suggested that splashed white was the result of a recessive gene, however this is no longer believed to be the case. It is more likely that many splashed whites go unidentified, whether because their markings are too minimal to register as "pinto" with breeders, confusion with sabino, or the confounding effect of multiple white spotting patterns.  It seems therefore more likely that splashed white is the result of an  incomplete dominant gene, with homozygotes exhibiting more extensive white than heterozygotes. Just as the presence of additional white patterning genes can increase the amount of white, other genes may be responsible for restricting the expression of splash.
  In addition, other patterns have a similar look: in particular, some forms of sabino and splash may be confused with each other, or the two patterns may exist in the same horse. In the Gypsy horse, the pattern called "blagdon" is described as "a solid colour with white "splashed" up from underneath." The genetic mechanisms behind certain traits, such as blue eyes in a few Arabian horses with otherwise minimal markings, have yet to be identified, though there is speculation that splash genes could be involved.
caption: A mare that tested positive for SW-1. Note the sabino-like jagged and lace-like pattern on the belly.
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