Lethal white syndrome


Good news!   

Your horse is clear of lethal white foal syndrome and does not have this gene mutation.   

Your horse cannot pass on this mutation. There are no breeding or performance implications.  

What is lethal white syndrome?

Lethal white syndrome affected foals seem healthy on delivery and birth is usually uneventful. Affected foals will feed but cannot use their undeveloped intestinal tract or defecate. Within 12 to 16 hours, foals will show signs of severe abdominal cramping and pain. The disease is extremely painful and distressing and there is no cure. Affected foals are usually humanely euthanized soon after birth, to spare them certain death because of a bacterial infection or rupture of the bowel.

Genomic Details

Overo lethal white syndrome is caused by the EDNRB gene. A change in this gene causes a lack of functioning nerves in the intestine. This leads to problems passing stool, an obstruction in the intestine, and severe colic. The same change in the EDNRB gene also alters skin cells, leading to a distinctive white coat pattern.

The mutation that causes overo lethal white syndrome is a switch in two of the four base pairs that make up a DNA molecule. Cytosine (C) and Thymine (T) are replaced by Adenine (A) and Guanine (G) changing the EDNRB gene. Therefore, a horse’s genetic result for overo lethal white syndrome is one of three possibilities:

  • TC/TC: Normal. Does not have the disease. Does not have the mutation.

  • TC/AG: Carrier. Does not have the disease. Carries one gene mutation from one parent. This might be passed to their foal.

  • AG/AG: Affected. Has the genetic disease. The horse has inherited a gene mutation from each parent. One mutation will be passed to their foal.