Lethal white syndrome

Lethal white syndrome (LWS), also known as overo lethal white syndrome (OLWS), overo lethal white foal syndrome (OLWFS), or lethal white overo (LWO), is a genetic disorder that primarily affects equine species, particularly American Paint Horses. The condition is linked to the frame overo (O) gene and is characterized by the birth of an all-white or nearly all-white foal, which typically dies within a few days due to intestinal tract abnormalities.

Causes

Lethal white syndrome is caused by a mutation in the endothelin receptor type B (EDNRB) gene. This mutation is inherited in an autosomal recessive manner, meaning that a foal must receive the defective gene from both parents to develop the condition. The mutation is associated with the frame overo (O) gene, which is responsible for a specific white spotting pattern in horses.

Symptoms

Foals with lethal white syndrome are typically born all-white or nearly all-white, with blue eyes. They may appear healthy at birth, but within a few hours, they begin to show signs of colic and other digestive problems. This is due to the fact that the mutation in the EDNRB gene causes a lack of nerve cells in the foal's intestines, preventing normal gut motility. As a result, the foal is unable to pass feces and develops a distended abdomen.

Diagnosis

Diagnosis of lethal white syndrome is typically based on the foal's physical appearance and symptoms. Genetic testing can also be used to confirm the diagnosis and to identify carrier horses.

Treatment and prognosis

There is currently no cure for lethal white syndrome, and treatment is generally supportive. This may include pain management for colic symptoms and intravenous fluids to prevent dehydration. However, due to the severity of the intestinal abnormalities, most foals with lethal white syndrome die or are euthanized within a few days of birth.

Prevention

Prevention of lethal white syndrome involves genetic testing to identify carrier horses. Breeding two carriers should be avoided, as there is a 25% chance that any foal they produce will have the condition.

See also

• Horse coat color genetics
• Equine coat color genetics
• List of genetic disorders in horses

External links

• UC Davis Veterinary Genetics Laboratory - Overo Lethal White Syndrome (OLWS)
• American Quarter Horse Association - Lethal White Overo Syndrome

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