"The American Paint Horse Association has three classifications for the various color patterns that occur on Paints. These classifications can be distinguished by the location of color on the horse. Overo horses generally have white under their bellies and on the sides of their abdomens and necks. The white usually does not cross the back of the horse. At least one leg, and often all four, will be the dark color. Head markings are often bald-, apron- or bonnet-faced and the white markings on the body tend to be scattered or splashy. The tail is usually one color."

"Overo Lethal White Syndrome (OLWS) is a condition that occurs in newborn foals. The condition is genetic, caused by a recessive gene, and both parents must carry a copy of the gene for a foal to be born with this defect. Horses that carry this gene are most commonly overo white patterned horses (frame overos), but there are exceptions. The defective gene has been found in American Paint Horses, American Miniature Horses, Half-Arabians, Thoroughbreds, and horses formerly called cropout Quarter Horses (foals born to registered Quarter Horse parents that have too much white to qualify for registration with the American Quarter Horse Association. This rule was removed from the AQHA at the 2004 Convention). The mating of two horses carrying the recessive gene will statistically result in a 25% chance of a lethal white foal.

OLWS foals have blue eyes and are completely or almost completely white at birth. These foals initially appear normal except for their unusual coloring. After a varying period of time, signs of colic will emerge due to the foal's inability to pass feces. The OLWS foal has an underdeveloped, contracted intestine caused by a failure of the embryonic cells that form nerves in the gastrointestinal system. These cells also play a role in determining skin color. There is no treatment for OLWS, and surgery to bypass the intestinal damage has never been successful due to the extensive nature of this type of lesion. Veterinarians advise euthanasia for all OLWS foals because death will inevitably occur from colic caused by fatal constipation.

OLWS is emotionally injurious and often financially devastating for small breeders because it is always fatal. The best way to ensure you will never lose a foal to OLWS is to have your mare(s) and stallion tested prior to breeding and never breed two carriers."

"NOT ALL all-white foals are lethal whites. It is possible to have a foal born pure white, without having the lethal white overo gene associate. This is generally recognized as being the maximum expression of the sabino patterning. There have been non-lethal white Paint foals that have been put down under the assumption that that they were LWO, when they could have in fact lived healthy, normal lives."

"A lethal white overo foal lacks black pigment in the skin. Foals have blue eyes, white hair and pink skin, but may have small pigmented skin spots or a few colored hairs.

This DOES sort of sound like the description of a Cremello or Perlino horse, (minus the small pigmented spots or colored hairs of course) doesn't it? But there IS a difference in the foal appearance. Cremello and Perlino foals are born a very light crème color, with blue eyes and pink skin. However, since they have crème colored hair, and NOT white, you can easily see any true white markings, such as socks, blazes, etc."

For more information on OLWS and testing please visit the following websites.

APHA

Overo Lethal White Syndrome

University of California - Davis

Lethal white syndrome - Wikipedia

Testing at UC Davis

Cremello Perlino Education Association