Lethal White Syndrome

Lethal White Syndrome

The lethal white syndrome is an autosomal (a chromosome that is not a sex chromosome) recessive defect mostly seen in a foal with two overo (American paint horse) parents. “Both parents must be carriers of one copy of the LWS allele in order for an affected foal to be born”. A foal with LWS is born appearing healthy other than a strange white (unpigmented) coat and blue eyes; however within 24 hours the foal will start to display signs of colic and within days with die. Foals suspected of being LW’s are often euthanized so not to suffer though a painful death. LWS is always lethal; through there are other color mutations that are not fatal that produce white foals.

The lethal white gene affects the order of the DNA that has to do with the development of the digestive tract. A horse’s digestive system consists of the cecum, the colon, as well as the rectum. “Necropsies on lethal white syndrome foals reveal a pale, underdeveloped colon and intestinal obstruction”. Tissue samples from colons of LWS foals have shown a lack of nerves that allow the intestine to move food through the digestive system. Carriers, which are heterozygous (have one copy of the mutated allele) can now be identified with a DNA test. Breeding two LWS heterozygous horses together should be avoided. Most Overo stallions are now tested for LWS so breeders can successfully avoid having LWS foals. It has been predicted that LWS will start affecting other breeds of horses more often, as a result of breeding for color, instead of physical traits (good conformation). In these horses, genetic variation is becoming less and negative genetic traits showing up more frequently.

The diagram below shows the possible results of two LWS heterozygous horses breeding.

Cite

http://www.petplace.com/horses/lethal-white-syndrome/page1.aspx

http://www.apha.com/breed/lethalwhites01.html

http://www.completerider.com/understandinggenes.htm

http://en.wikipedia.org/wiki/Lethal_white_syndrome

p://stallingspainthorses.com/lethal-white1.htm

http://www.netpets.org/horses/healthspa/lethal.html


I wrote this for Biology class, it  was awesome to finally use some of my horsey knowledge for academic purposes!