Junctional Epidermolysis Bullosa (JEB)

What is junctional epidermolysis bullosa?

Junctional epidermolysis bullosa (JEB) is a progressive inherited skin disorder primarily seen in Belgian Draft Horses and American Saddlebreds. Also known as red foot disease, hairless foal syndrome, and epitheliogenesis imperfecta (EI), affected foals develop severe blistering and skin lesions at pressure points. These lesions worsen with time, and foals are at risk of severe infections.

Junctional epidermolysis bullosa is inherited as a recessive trait. A mutation (JEB1) has been identified in Belgians and related breeds that affects the production of proteins that anchor the skin to the underlying tissue. A different mutation (JEB2) is responsible for the condition in American Saddlebreds. DNA tests are available for both mutations.

What are the clinical signs of junctional epidermolysis bullosa?

Foals affected with JEB are born alive, and clinical signs may be evident at birth or shortly thereafter. Skin blisters turn into lesions at pressure points and progress over time. Foals with JEB often develop secondary infections. In severe cases, the hoof wall may detach, leading to sloughing of the hoof. Affected foals are often born with front teeth (premature eruption of teeth) and are prone to developing oral ulcers.

How is junctional epidermolysis bullosa diagnosed?

Diagnosis of JEB may be based on a combination of characteristic clinical signs in breeds known to be affected, and diagnostic testing. Skin biopsies may be taken to identify the separation of skin layers. A definitive diagnosis of JEB can be made through genetic testing.

How is junctional epidermolysis bullosa treated?

There is no treatment for JEB and most affected foals are euthanized.

What is the prognosis for junctional epidermolysis bullosa?

Junctional epidermolysis bullosa is a fatal condition. Affected foals are euthanized or succumb to infection by 10 days of age.

How can junctional epidermolysis bullosa be prevented?

Junctional epidermolysis bullosa can be prevented by performing DNA testing of sires and dams prior to breeding to avoid producing affected offspring. The condition is autosomal recessive, meaning that an affected animal receives one copy of the JEB mutation from each parent (N/J). Since affected animals (J/J) do not survive to breeding age, JEB foals are produced by matings between carriers (N/J x N/J). Carriers do not develop the disease, but they have a 50% chance of passing the mutation on to their offspring. Carriers do not need to be removed from the breeding pool. A successful breeding program can use matings of carriers (N/J) to non-carriers (N/N) without the worry of producing an affected foal. These breedings will produce 50% normal (N/N) and 50% carrier (N/J) offspring.

The JEB1 test is mandatory for all breeding stallions and mares for registration with the Belgian Draft Horse Corporation of America. Carriers have also been identified in other related breeds, including the Breton, Comtois, Vlaams Paard, and Belgische Koudbloed Flander draft horse breeds.

For more information:

University of California, Davis, Veterinary Genetics Laboratory, JEB1 testing (Belgians)

University of California, Davis, Veterinary Genetics Laboratory, JEB2 testing (Saddlebreds)

*This article may not be reproduced without the written consent of the UC Davis Center for Equine Health. Please email requests to cehadmin@ucdavis.edu.