Lethal White Syndrome - Clinical Signs

Clinical Signs

Unlike some coat color dilution lethals, which may result in premature births, stillborn, or weak foals, foals born with lethal white syndrome appear to be fully formed and normal. The coat is entirely or almost entirely pure white with underlying unpigmented pink skin. Pigmented regions may be any color, and if present are most common around the muzzle, underside of the barrel, and the hindquarters or tail. The eyes are blue. A few lethal white foals have been shown to be deaf.

Healthy foals pass meconium, the first stool, soon after birth, though some healthy foals may require an enema to assist this process. But the meconium of LWS foals is impacted high in the intestine, and never appears, even with the use of enemas. Symptoms of colic begin to appear within the first day, and all LWS-afflicted foals die within the first few days of life. The painful and inevitable death that follows usually prompts veterinarians and owners to euthanize foals suspected of having lethal white syndrome.

Death is caused by an underdeveloped part of the digestive system. The large intestine of the horse is a complex system where most digestion takes place, and comprises the cecum, the colon, and the rectum. Necropsies on lethal white syndrome foals reveal a pale, underdeveloped colon and intestinal obstruction (impaction). Samples of affected tissue show a lack of nerves that allow the intestine to move material through the digestive system, a condition called intestinal agangliosis.

Closer examination of the skin and hair shows both to be unpigmented, and most hair follicles are inactive and many are devoid of hair altogether. All Lethal White Syndrome foals test homozygous for a genetic abnormality.