Junctional Epidermolysis Bullosa (JEB)

JEB is a condition found in American Saddlebreds and certain other light breeds of horses. It results in a lethal skin condition in affected foals. The foals must inherit the mutation from both parents. A test to identify carriers is now available. The mutation was discovered at UK Genetic Testing at Gluck with support from the American Saddlebred Horse Association. The mutation for the Saddlebred form of JEB is different than that for the Belgian Horse JEB.  We offer only the Saddlebred JEB test. Carriers can be safely bred as long as they are not bred to another carrier. Cost: $50 from blood or hair samples.

Photo of foal affected with JEB
JEB affected foal. 
Photo courtesy of the American Saddlebred Horse Association.

Overo Lethal White Syndrome (OLWS)

This is so named because affected foals are all white or near white at birth and have improperly formed rectal tissue resulting in death or requiring euthanasia at a few days of age. It is caused by a mutation that in the heterozygous form results in a frame overo pattern. Therefore the color pattern is very desirable for Paint or Pinto horse breeders. There are no health effects for carriers. However if two carriers are bred 25% of the foals on average will be homozygous for the mutation and will be affected. Although most common in Paint horses and Quarter horses, the mutation has been found in Tennessee Walking Horses as well.


An inherited neuromuscular disorder has been identified in New Forest ponies (Wijnberg ID et al., 2011) which is caused by an autosomal recessive mutation in the CLCN1 gene. Carriers of the mutation appear normal, but when two carriers are mated there is a 25% chance that an affected foal will be produced. Affected foals have abnormal muscle activity and spend more time than usual laying down and also exhibit gait abnormalities. In cooperation with Dr. Cord Drögemüller in Switzerland, UK Genetic Testing at Gluck is offering this test. Please see the submission form for instructions on submitting a sample.