Dominant White Mutations – W5, W10, W13, W20, and W22

Quick Summary

Dominant white is a variable white spotting pattern caused by many different mutations in the KIT gene. The VGL tests for the five most common mutations known as W5, W10, W13, W20, and W22. Homozygosity for W5, W10, W13 or W22 is thought to be non-viable.

Horse displaying a dominant white coat color.

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Phenotype: Dominant white causes a variable white coat patterning phenotype that typically ranges from extensive white face and leg markings with or without roaning and/or white patches on the belly to an all-white horse. Some alleles are expected to be lethal in homozygotes.

Mode of Inheritance: Autosomal dominant

Alleles: N = Normal, W5 = Dominant white 5, W10 = Dominant white 10, W13 = Dominant white 13, W20 = Dominant white 20, W22 = Dominant white 22

Breeds appropriate for testing: W5, W22 = Thoroughbred and Thoroughbred crosses. W10 = Quarter Horses and related breeds including Paint Horses, Appaloosas, and Pony of the Americas. W13 = Quarter Horses and related breeds, Shetland Pony and Miniature Horses. W20 has been identified in many horse breeds so nearly all breeds are appropriate for testing.

Explanation of Results:

  • Horses with N/N genotype do not have a white spotting pattern caused by W5, W10, W20, or W22. If this horse has a white spotting pattern, it is caused by some other genetic mechanism.
  • Horses with N/W5, N/W10, or N/W22 genotypes will display a dominant white spotting pattern that can vary from large amounts of white face and leg markings to a horse that is almost completely white.
  • Horses with N/W13 genotype display a dominant white spotting pattern and are reported most often to be all white with pink skin.
  • Horses with W5/W20, W10/W20, W13/W20, or W20/W22 genotypes will display a dominant white spotting pattern and are typically all white.
  • Horses with N/W20 or W20/W20 genotype display white face and leg markings and some may have a variable amount of white spotting. It is thought that horses with these genotypes that have more extreme white spotting patterns likely have mutations in other pigmentation genes.
  • Horses with W5/W5, W10/W10, W13/W13W22/W22 are thought to be embryonic lethal, therefore it is advisable to not mate horses with W5, W10, W13, or W22 alleles to each other.


$40 one test per animal
+ $15 each additional coat color/type test on the same animal

Panels Available
Turnaround Time
At least 15 business days; may be delayed beyond 15 business days if sample requires additional testing, or a new sample is requested.
Additional Details

The KIT gene has crucial function for the development of many cell types, including blood and pigment cells (melanocytes). Mutations that affect normal functioning of the KIT protein often result in lack of melanocytes in the skin and hair follicles, which leads to white patterning in horses known as dominant white.

Dominant white patterns are variable, ranging from extensive face and leg markings with or without minimal sabino-like patterns, including roaning on the belly and/or belly spots, to an all-white horse. Eye color of dominant white horses is typically brown.

A number of different KIT mutations associated with white patterns have been identified in the horse. These include dominant white, Sabino-1, and Tobiano. To date, 34 of these mutations have been characterized as dominant white mutations and can range from alleles that have a minimal impact on coat patterning to those causing an all-white phenotype. Many of the dominant white mutations arose recently and are therefore restricted to specific lines within breeds. The exceptions include W13 and W20. W13 (c. 2807+5G>C) was originally identified in the Quarter Horses but has also been reported in several other breeds including the Australian Miniature Horse, the American Miniature Horse, and the Shetland Pony. W20 (c.2045G>A) has been reported in many breeds. 

W5 (c.2193delG) is found in descendants of the Thoroughbred stallion Puchilingui. W10 (c.1126_1129delGAAC) is found in descendants of the Quarter Horse stallion GQ Santana. W22 (Chr3:79548925-79550822del1898insTATAT) is found in descendants of the Thoroughbred stallion Airdrie Apache.

The majority of the dominant white mutations identified are thought to be detrimental to KIT protein function. When horses have one copy of these mutations they have a reduced number of melanocytes and thus have a white spotting pattern. However, when they have two copies of the mutation (homozygous), it is believed that reduction or absence of KIT signaling occurs, affecting more than just the pigment cells. For example, horses homozygous W5, W10, W13, and W22 are likely embryonic lethal. However, this remains to be confirmed. It is unknown if horses that are compound heterozygotes (two different mutations in the same gene, i.e. W5/W10, W5/W13, W5/22, W10/W13, W10/W22, or W13/W22) are viable, and testing through the VGL has yet to identify horses with these genotypes.

W13 (c. 2807+5G>C) was initially identified in a Quarter Horse X Paso Peruano cross-bred family that had two white horses, and pedigree data in that study determined that the W13 mutation likely arose on the Quarter Horse background. Later, W13 was found to be responsible for the white phenotype in a family of Australian Miniature Horses. A recent study led by VGL director, Dr. Rebecca Bellone, identified 14 all-white American Miniature Horse and one Shetland Pony whose all-white coats were explained by the W13 mutation. All horses were heterozygous for W13 (N/W13) and had pink skin. Genotyping a random sample of 80 American Miniature Horses revealed a W13 allele frequency of 0.0063 (1 N/W13 horse and 79 N/N horses). W13 was not identified in any of 59 randomly selected Shetland Ponies. No W13/W13 homozygous horses have been identified to date, suggesting this may be embryonic lethal.

W20 (c.2045G>A) is a much older mutation and is found in many breeds. This mutation is thought to have a more minor effect on protein function as well as a subtler effect on the amount of white expressed unless in combination with other dominant white alleles (and perhaps other white spotting genes). In combination with other white pattern alleles, W20 has been shown to increase the amount of white patterning, producing an all-white or nearly all-white phenotype. Unlike W5, W10 and W22, the homozygous condition W20/W20 is not lethal.

W22 (Chr3:79548925-79550822del1898insTATAT) occurs on the W20 background, that means that all horses with the W22 mutation also have the W20 mutation. Since the W22 mutation has a greater impact on protein function than W20, the reported allele is W22 even though, technically, both the W20 and W22 variants are present. In the case where a horse inherits a W20 from one parent and a W20 and W22 from the other parent (technically meaning it has two copies of W20 and one copy of W22), it will be reported as a compound heterozygote, W20/W22. Horses with this genotype have been shown to have an all-white phenotype. 

The Veterinary Genetics Laboratory offers tests for W5, W10, W13, W20, and W22 mutations to owners who want to breed horses for dominant white or to determine the genetic status of horses with white patterning.


Type of Sample



Akhal Teke American Sport Horse American Sport Pony American Warmblood Andadura Andalusian Appalachian Singlefoot Appaloosa Appendix Arabian Ardennes Arriador Australian Stock Horse Azteca Baden-Wurttemberg Barockpinto Baroque Pinto Bashkir Curly Bavarian Belgian Belgian Sport Horse Belgian Warmblood Brandenburg Breton British Sport Horse British Spotted Pony Bucking Horse Burchell's Zebra Caballo Deportivo la Silla Camarillo White Canadian Horse Canadian Warmblood Caspian Horse Chapman's Zebra Chilean Horse Cleveland Bay Clydesdale Cob Normand Coldblooded Trotter Colorado Ranger Comtois Connemara Pony Continental Warmblood Costa Rican Paso Horse Cream Draft Criollo Crossbred Curly Dales Pony Danish Warmblood Deutsches Reitpony Deutsches Sportpferd Draft Cross Dutch Harness Horse Dutch Warmblood Exmoor Pony Falabella Faux Friesian Fell Pony Finnhorse Fire Friesian Frederiksborg French Warmblood "Selle Francais" Friesian Friesian Cross Friesian Sporthorse Georgian Grande German Riding Pony Gotland Pony Grevy's Zebra Gypsian Gypsy Cob Gypsy Vanner Hackney Horse Hackney Pony Haflinger Half Andalusian Half Arabian Half-Marchador Hanoverian Hartmann's Zebra Heck Tarpan Hessen Hibrido Holsteiner Iberian Warmblood Iceland Pony Icelandic Horse Imperial Heritage Horse International Sport Pony Irish Draught Irish Hunter Kallblodstravare Kentucky Mountain Horse Kerry Bog Pony Kiang Kiger Mustang Knabstrupper Kulan Latvian Warmblood Lipizzaner Lusitano Mangalarga Mangalarga Marchador Mexican Sport Horse Miniature Horse Missouri Fox Trotter Mongolian Domestic Horse Morab Morgan Horse Moriesian Moroccan Barb Mountain Pleasure Horse Mule Mustang National Show Horse New Forest Pony Newfoundland Pony Nokota Noriker North American Trakehner Norwegian Fjord Horse Norwegian Nordland Oldenburg Onager Other Paint Horse Paso Fino Percheron Performance Horse Int'l Peruvian Horse Pinto Polish Warmblood Pony of the Americas Przewalski Pura Raza Española Quarter Horse Racking Horse Rheinland Rheinland Pfaltz-Saar Rhenish German Coldblood Rocky Mountain Horse Russian Orloff Russian Warmblood Saddlebred Saxon-Thuringian Coldblood Scottish Highland Pony Selle Français Shetland Pony Shire Shire Crossbred Silesian Horse Sillo Argentino Single-Footing Horse South German Coldblood Spanish Barb Spanish Heritage Horse Spanish Mustang Sporthorse Spotted Saddle Horse Standardbred Suffolk Punch Swedish Warmblood Tarpan Tennessee Walking Horse Thailand Pony Thoroughbred Trakehner Trocha Trocha y Galope Trote y Galope Turbo Friesian Unknown Uruguayan Criollo Virginia Warmblood Warlander Welsh Pony Weser Ems Ponies Westfalen Wild Horse Zangersheide
+ View All Breeds
Type of Test
Coat Color and/or Type
Results Reported As

Test Result

DOMINANT WHITE (W5, W10, W13, W20, W22)



No copies of W5, W10, W13, W20 or W22 detected.


1 copy of W10 detected.


2 copies of W10 detected.*


1 copy of W5 detected.


1 copy of W5 and 1 copy of W10 detected.# * 


1 copy of W5 and 1 copy of W20 detected.


2 copies of W5 detected.*


1 copy of W10 and 1 copy of W20 detected.


2 copies of W20 detected.


1 copy of W20 detected.


1 copy of W22 detected.


2 copies of W22 detected.*


1 copy of W5 and 1 copy of W22 detected. # *


1 copy of W10 and 1 copy of W22 detected. # *


1 copy of W20 and 1 copy of W22 detected.&


1 copy of W13 detected.


2 copies of W13 detected.*


1 copy of W5 and 1 copy of W13 detected. # *


1 copy of W10 and 1 copy of W13 detected. *


1 copy of W13 and 1 copy of W20 detected.


1 copy of W13 and 1 copy of W22 detected. *

* Homozygous W5/W5, W10/W10, W13/W13, or W22/W22 horses may be embryonic lethal and thus not viable. This result may only be found in aborted fetuses produced in matings between two horses that have W5, W10, W13 or W22 variants. Similarly, compound heterozygotes for these variants may also be embryonic lethal.

# Not all expected combinations of dominant white mutations have been observed but are possible if mating pairs possess different variants.

& The W22 allele occurs on the W20 background. Since W22 has a more pronounced impact on white pattern, we only report that allele as W22. 


Haase, B., Brooks, S.A., Schlumbaum, A., Azor, P.J., Bailey, E., Alaeddine, F., Mevissen, M., Burger, D., Poncet, P.A., Rieder, S., & Leeb, T. (2007). Allelic heterogeneity at the equine KIT locus in dominant white (W) horses. PLoS Genetics, 3(11): e195. doi: 10.1371/journal.pgen.0030195

Haase, B., Brooks, S.A., Tozaki, T., Burger, D., Poncet, P.A., Rieder, S., Hasegawa, T., Penedo, M.C., & Leeb, T. (2009). Seven novel KIT mutations in horses with white coat colour phenotypes. Animal Genetics, 40(5), 623-629. doi: 10.1111/j.1365-2052.2009.01893.x

Haase, B., Rieder, S., Tozaki, T., Hasegawa, T., Penedo, M. C., Jude, R., & Leeb, T. (2011). Five novel KIT mutations in horses with white coat colour phenotypes. Animal Genetics, 42(3), 337-339. doi: 10.1111/j.1365-2052.2011.02173.x

Hauswirth, R., Jude, R., Haase, B., Bellone, R.R., Archer, S., Holl, H., Brooks, S.A., Tozaki, T., Penedo, M.C.T., Rieder, S., & Leeb, T. (2013). Novel variants in the KIT and PAX3 genes in horses with white‐spotted coat colour phenotypes. Animal Genetics, 44(6), 763-765. doi: 10.1111/age.12057

Negro, S., Imsland, F., Valera, M., Molina, A., Solé, M., & Andersson, L. (2017). Association analysis of KIT, MITF, and PAX3 variants with white markings in Spanish horses. Animal Genetics, 48(3), 349-352. doi: 10.1111/age.12528

Dürig, N., Jude, R., Holl, H., Brooks, S.A., Lafayette, C., Jagannathan, V., & Leeb, T. (2017). Whole genome sequencing reveals a novel deletion variant in the KIT gene in horses with white spotted coat colour phenotypes. Animal Genetics, 48(4), 483-485. doi: 10.1111/age.12556

Hoban, R., Castle, K., Hamilton, N., & Haase, B. (2018). Novel KIT variants for dominant white in the Australian horse population. Animal genetics49(1), 99–100. doi: 10.1111/age.12627

Esdaile, E., Kallenberg, A., Avila, F., & Bellone, R. R. (2021). Identification of W13 in the American Miniature Horse and Shetland Pony Populations. Genes, 12(12), 1985. doi: 10.3390/genes12121985

Avila F, Hughes SS, Magdesian KG, Penedo MCT, Bellone RR. Breed Distribution and Allele Frequencies of Base Coat Color, Dilution, and White Patterning Variants across 28 Horse Breeds. Genes. 2022; 13(9):1641. doi: 10.3390/genes13091641