Sabino 1 and
Dominant White Spotting Patterns W1-W23+
This page is under construction. It will contain extensive information on the KIT mutations: Sabino 1 and the horse Dominant White patterns W1-W23+. We are looking for pictures of horses that are representative of the various common patterns. For a photo to be chosen the horse must be clean, unclipped, and standing in a conformation type stance that best shows off the pattern. Photos also need to have the horse's name and owners name at a minimum.
Sabino 1 (Sb1): Sabino 1 was the first of the white spotting patterns to be identified. It was named when the thought was that there would only be a few Sabino-like patterns on the KIT gene. Researchers have since determined that the KIT gene has a high rate of mutation, so a White Spotting designation with a number system has since been adopted: W1 thru W23 so far. Clydesdale Horses were part of the original testing group but were found to not carry Sabino 1(Sb1) even though they typify the standard sabino pattern. Sabino 1 (Sb1) should probably have been re-designated as W1 but this would likely have caused a great deal of confusion. Sabino in Spanish means “pale” or “speckled” as in egg-like. The Sabino 1 (Sb1) pattern generally has white hooves and legs, with the white extending up the front of the rear leg and the back of the foreleg in ragged patches onto the horses body from the belly. The horse generally also has a wide blaze that reaches to the eyes and can cause partial blue eyes, there is often white chin spotting as well. Often there are belly spots of varying sizes in irregular or fragmented patches, flecks, additional body patches and roaning. Sabino 1 (Sb1) can also imitate Tobiano (To) or Frame Overo (O/o). Minimal expression can be as small as white socks/ stockings with ragged edges or a long narrow extension to the sock and a blaze face. Heterozygous Sabino 1 tends to appear as flashy white face and leg markings with some roaning. Homozygous Sabino 1 causes a more white marked horse that may be almost pure white with only a small amount of colour left along the topline, especially in the mane and ears. Homozygous Sabino 1 is not life threatening.
Genetics: Sabino 1 is caused by a splice variant on Intron 16 of the KIT gene that effects exon 17.
Breeds: Tennessee Walking Horse, Missouri Foxtrotter, Rocky Mountain Horse and related breeds, Gypsy Cob, Miniature Horse, Paint Horse, Aztecas, Shetland Pony, Spanish Mustang, Pony of the Americas.
White Spotting Patterns (W1- W23+): In the past this group/category of patterns was referred to as Dominant White because the white in the pattern covers (dominates) the coloured parts of the horse, a geneticist would say “inherited as a monogenic autosomal dominant trait that shows a variable expression of coat depigmentation”. Many people found the concept of dominant white confusing since often the patterns are Sabino-like and do not create a predominantly white horse which is what they thought Dominant White should be, with this being said, most horses are 50% white or greater. The white spotting patterns range from Sabino-like to near-white to fully white. Sabino-like is generally typified as high white stockings on the horse diminishing into spears at the top, patches of white on the underbelly, a large wide blaze with chin spots, blue or partial blue eyes, and sprinklings of roan like hairs or patches and flecks of white on the body. Most of the types have brown eyes, however many of the originators had blue eyes and blue eyes appear sporadically. They are all on the KIT gene in varying locations and most are associated with a single known founding horse and therefore continue in known family lines. Thus far most of the W# patterns have been Heterozygous with the exception of W20. It is suspected that most of the W# patterns will prove to be embryonic lethal. Any mutation/ change that causes complete loss of function to the KIT, gene will cause prenatal or perinatal death due to anemia.
KIT: The white spotting pattern gene KIT (Mast/ Stem Cell Growth Factor Receptor) is located on Chromosome 3 and has 21exons. At this time it is felt that a horse can only have 2 KIT gene mutations, 1 from each parent, or else the gene will have too much mutation and will not function correctly. It is still possible to have 2 KIT mutations and any of the other white patterns as these are on different genes. “The KIT gene is a complex and relatively large molecule (and the gene is long and complex with many interspersed non-coding regions called Introns, allowing for the high number of observed mutations). It is important in the control of cell differentiation, proliferation, survival and motility. It is necessary for the development and survival of melanocytes, mast cells, sperm cells and cells of the gastrointestinal tract” (Raskoski,2005). Simply put the KIT gene is crucial for the development of blood, gonadal and pigmentary cells. The KIT gene has 21 exons so the possible mutations available are huge.
Genetics: Preferred name: Mast/Stem Cell Growth Factor Receptor. Also known as v-kit Hardy-Zukerman 4 feline sarcoma viral oncogene
homolog [Equus Caballus (horse)], c-kit and tyrosine kinase receptor homolog.
Map Location: ECA3q21-22
NCBI: Gene ID: 100009704; Location: Chr 3 NC_009146.2 (77727979…77809750, complement); Length: 81,612 bp
Ensembl: Gene ID: ENSECAG 00000012032; Location: complement (77730011…77809756); Length: 79,746 bp
|W1||Franches Montagnes||Cigale (1957)||Born white or with a small amount of colour that whitens with age|
|W2||Thoroughbred||KY Colonel (1946)*||Completely white|
|W3*||Arabian||R Khasper (1996)||Mostly white or may be slightly coloured|
|W4||Camarillo White||Sultan (1912)||Born white or with a small amount of colour that whitens with age|
|W5||Thoroughbred||Puchilingui (1984)*||Range from completely white to sabino-like|
|W6||Thoroughbred||------||One horse who is almost completely white|
|W7||Thoroughbred||------||One horse who is almost completely white|
|W8||Icelandic||Thokkadis||One horse who is mottled Sabino-like|
|W9||Holstein Horse||------||One horse who is completely white|
|W10||Quarter Horse||GQ Santana (2000)*||Range from nearly all white to small amounts of white on the legs|
|W11||South German Draft||Schimmel||Nearly all white|
|W12||Thoroughbred||------||One foal who died at 5 weeks, Sabino-like|
|W13||¼ Horse/Paso Peruano||------||Completely white|
|W14||Thoroughbred||Shirayukihime (1996)||Range from completely white to mostly white|
|W16||Oldenburg||O’Wie Weiss (2009)?||Almost completely white|
|W17||Japanese Draft||------||One completely white horse with one blue eye|
|W18||Swiss Warmblood||Colorina Von Hof||Sabino with extended white speckled areas|
|W19||Part Arabian||Fantasia Vu (1990)||Bald face, extended white legs, irregular belly spots|
|W20*||Icelandic||------||One colt that is patchy Sabino-like|
|W22||Thoroughbred||Airdrie Apache (1993)*||Very Sabino-like, highly expressed Sabino-roan|
|W23||Arabian||------ (1989)||Mostly white|
W2: KY Colonel was a highly expressed Sabino-like but all of the horses with his spotting pattern are pure white: White Beauty (1963), Patchen Beauty, and The White Fox etc.
W3: is a c.706A>T mutation
W5: common bloodline so genetic testing is available to the public
W10: GQ Santana is registered with both the AQHA and the APHA. Homozygous forms may not be viable, more testing is being done. Common bloodline so genetic testing is available to the public
W15: It is postulated that Rhocky Rhoad was the founding horse but Rhevelation (2008), his son was the actual horse tested. Rhocky Rhoad is by Khartoon Khlassic (1996) who is by Khemosabi who goes back to Ferseyn. Cherie Lonas Mamula, owner of Rhocky Rhoad and breeder of Rhevelation believes that W15 goes back to Ferseyn based on what she has seen in her breeding program.
W20: suspected to be in many breeds. Pattern is not recognised as a pinto pattern. Heterozygous forms have white socks and a large blaze while homozygous forms have higher socks and a larger blaze/bald face and can be more Sabino-like. Seems to enhance white when paired with other white spotting patterns. Common pairing situation is with W5. Clydesdale and Shire breeders traditionally would breed a horse with 4 white feet and often a more roaned body (homozygous) to a horse with 1 dark foot (heterozygous) to produce a horse with the desired white feet, blaze and no body white. Common breeds: Appaloosa, Clydesdale, Franches-Montagne, German Riding Pony, German Warmblood, Gypsy Cob, Marwari, Morgan, Noriker, Old Tori, Oldenberg, Quarter Horse, Paint Horse, Paso Peruano, South German Draft, Thoroughbred, Welsh Pony.
W22: While Airdrie Apache is currently credited as the founding horse, his Dam, “Not Quite White”, born in 1989, is the more likely originator.