Overo lethal white gene

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Fox with Overo spotting
Navajo boy on a bay with weak Frame Overo-spotting - note the stain on the neck

The Overo-Lethal-White-Gene is a gene that is involved in the inheritance of coat color in horses. It is inherited in an incompletely dominant manner and is caused by a mutation in the endothelin receptor B locus, leucism . A horse that receives this gene only once will usually show frame-over-spotting and be healthy. If the lethal white gene is inherited from both parents (i.e. if it is homozygous), it leads to OLWS (Overo lethal white syndrome).

Races and colors in which the gene can appear

Blackfooth Chief on a Frame Overo

Well over 90% of Frame-Overos, Highly-White-Calico-Overos and Frame-Blend-Overos carry the gene.

If a horse also has the Tobiano gene, it usually shows a Tobiano check and not an Overo check.

A frame-overo gene can also exceptionally be present in various other spotted patterns and even in monochrome animals without the spotting being clearly identifiable. In the samples Sabino , Minimally-White-Calico-Overo, Splashed White Overo , Nonframe-Blend-Overo and in unchecked horses of the breeds in which the Overo check occurs, the proportion of gene carriers is below 20%. The gene is not found in breeds without a spotted pattern .

It is therefore advisable to test all horses of breeds in which frame-overos occur for this gene to make sure that you do not cross two carriers of this gene without knowing it.

Lethal White Foal Syndrome

If the lethal white gene is inherited from both parents (i.e. if it is homozygous), it leads to OLWS (Overo lethal white syndrome). Such foals are completely white. Since the nerve cells have not migrated out of the neural tube correctly, the gastrointestinal tract is not adequately supplied with nerve cells. They are absent at the end of the small intestine ( end of the ileum), in the appendix and the entire large intestine. This leads to an intestinal obstruction, which is why the large intestine expands ( megacolon ), and which ultimately leads to the death of the foal from colic. Lethal-White-Foal Syndrome corresponds to Hirschsprung's disease in humans. The foals die from it within the first days of life.

Frame overo

Frame overo

The term Frame-Overo (Fr and fr) from "Frame", which means "frame" in English, comes from the fact that the white part of the spotting is on the side of the horse's body and neck and looks like it is framed by the dark areas. No white spot crosses the back line, only on the neck the white spots sometimes cross the mane crest. At least one leg, but often all four are dark. The face often has very distinctive markings like a lantern. The spots are usually irregular, as if frayed.

Other Overo piebalds

In addition to the frame Overo gene, there are other genes that can cause Overo spotting. For example, Splashed White is also assigned to the Overo check, although it has a different genetic cause. Likewise were Sabinoschecken associated with the Overo form circle. Conversely, not every horse with the frame overo gene has a frame overo check.

See also

Web links

Individual evidence

  1. ^ GC Yang, D. Croaker, AL Zhang, P. Manglick, T. Cartmill and D. Cass: A dinucleotide mutation in the endothelin-B receptor gene is associated with lethal white foal syndrome (LWFS); a horse variant of Hirschsprung disease (HSCR). In: Human Molecular Genetics . 1998, Vol. 7, No. 6, pp. 1047-1052. doi : 10.1093 / hmg / 7.6.1047
  2. ↑ a b D. L. Metallinos, AT Bowling, J. Rine: A missense mutation in the endothelin-B receptor gene is associated with Lethal White Foal Syndrome: an equine version of Hirschsprung disease. In: Mammalian genome. Volume 9, Number 6, June 1998, pp. 426-431, ISSN  0938-8990 . PMID 9585428 .
  3. ↑ a b c d T. Lightbody: Foal with Overo lethal white syndrome born to a registered quarter horse mare. In: The Canadian veterinary journal. La revue vétérinaire canadienne. Volume 43, Number 9, September 2002, pp. 715-717, ISSN  0008-5286 . PMID 12240532 . PMC 339559 (free full text).
  4. ↑ a b c d E. M. Santschi, PD Vrotsos, AK Purdy, JR Mickelson: Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses. In: American journal of veterinary research. Volume 62, Number 1, January 2001, pp. 97-103, ISSN  0002-9645 . PMID 11197568 .
  5. ^ EM Santschi, AK Purdy, SJ Valberg, PD Vrotsos, H. Kaese, JR Mickelson: Endothelin receptor B polymorphism associated with lethal white foal syndrome in horses. In: Mammalian genome. Volume 9, Number 4, April 1998, pp. 306-309, ISSN  0938-8990 . PMID 9530628 .
  6. ↑ BD Hultgren: Ileocolonic aganglionosis in white progeny of overo spotted horses. In: Journal of the American Veterinary Medical Association. Volume 180, Number 3, February 1982, pp. 289-292, ISSN  0003-1488 . PMID 7056678 .
  7. ↑ L. McCabe, LD Griffin, A. Kinzer, M. Chandler, JB Beckwith, ER McCabe: Overo lethal white foal syndrome: equine model of aganglionic megacolon (Hirschsprung disease). In: American journal of medical genetics. Volume 36, Number 3, July 1990, pp. 336-340, ISSN  0148-7299 . doi : 10.1002 / ajmg.1320360319 . PMID 2363434 .
  8. ↑ Laurie Fio, The Horse Report Vol 12, No. 2 October 1994.