Scientists Find Lethal White Gene

By Rebecca Overton
from the January 1998 Paint Horse Journal

Researchers conducting a study funded by the American Paint Horse Association have made a significant discovery about how lethal white syndrome is inherited.

The Equine Genetics Group at the University of Minnesota has determined the gene and DNA mutation associated with the dreaded condition that has plagued the Paint Horse breed.

The gene is associated with white-spotted coat patterns and intestinal nerve defects in several species. Analysis of the DNA sequence of this gene in affected foals and their parents has revealed that each parent has one copy of the mutant gene, while all affected foals have two copies, explained Dr. Elizabeth Santschi, one of the researchers.

"This new information means owners of carrier mares and stallions could make more informed decisions about who they want to breed to," said Santschi.

"Now we're trying to find out what incidence of this mutant gene occurs in all color patterns."

Lethal white syndrome has been an elusive shadow that has dogged breeders of Paint Horses. Foals afflicted with it are primarily of overo lineage. They are born all white or mostly white.

Although the foal may seem normal at birth, it usually begins showing signs of colic within 12 hours because of a non-functioning colon. Because the syndrome is always fatal, lethal white foals are often euthanized.

In November 1996, the APHA Executive Committee approved a $7,650 grant to fund a proposal by the University of Minnesota researchers who wanted to describe the inheritance of the syndrome and locate the gene responsible.

Now that the culprit has been located, the researchers are testing large numbers of Paint Horses to determine the prevalence of the normal and mutant (lethal) gene.

As more results become available, the APHA will share the information on lethal white syndrome with its members.