Skin Detectives.

Root of devastating skin disorder in Belgian horses is identified.

An article by Clare Illingworth and Kristy Nudds.


The century-long curse of a fatal genetic disease that affects the newborn foals of several draught horse breeds may soon be broken.

The genetic mutation responsible for caus-ing junctional epidermolysis bullosa (JEB) — a devastating skin disease in which skin layers can’t adhere to one another — has been iden-tified by Prof. John Baird, Department of Clini-cal Studies, and researchers at France’s Institut National de la Sant? et de la Recherche M?di-cale (INSERM).

They’ve developed a test for screening carriers of the mutated gene. Testing will soon begin for all colts born after January 2003 in the most affected breed, the Belgian.

“By testing future breeding stock, we can manage breeding practices so that carriers can be removed from the gene pool of Belgians, with the hopes of eliminating the disease in North America’s population,” says Baird.

An estimated 30 to 35 per cent of Belgian horses in North America are JEB carriers. Baird became interested in finding the disease’s cause after seeing its devastating effects in a Belgian foal brought to the Ontario Veterinary College several years ago.

When a foal inherits the mutated gene from both parents, it lacks a skin protein known as Laminin-5, which normally interacts with collagen to help connect the various layers of the skin. Affected foals suffer from painful skin sores and lesions, particularly in the fetlock, stifle and hock areas. JEB also affects the epidermal surfaces of organs and causes mouth and tongue ulcers. Death usually occurs within a week of birth.
The affliction was first described in the Ardenner breed (an ancestor of the Belgian) in the 1930s by Swedish veterinarians. Sus-pecting it had a genetic cause, but limited by lack of DNA technology, they began recording pedigrees so they could trace the disease.

Those pedigrees have proved extremely useful to Baird. Extensive reviews allowed him to trace the ancestors of reported cases and identify which animals were carriers. He determined that the mutation began in sev-eral well-used sires, starting in the late 1800s. These sires are ancestors of nearly all Belgians and were mated with several other draught breeds as well, he says.

Baird collected DNA samples of known carriers and sent them to INSERM geneticist Guerrino Meneguzzi, who used the samples to identify the precise location of the muta-tion responsible for JEB. A simple, reliable test was then developed that requires only hair (including the root, which contains DNA) be taken from the horses. The test involves the same procedure currently used to identify the genetic disorder equine hyperkalemic peri-odic paralysis, which originated in the North American quarter horse population.

Baird presented his findings to both the American and Canadian Belgian Horse asso-ciations last summer. Genetic testing will soon be offered by the University of California’s Veterinary Genetics Laboratory in Davis under a licence agreement.

“This disease is not only a welfare concern, but it also costs the Belgian horse industry thousands in lost revenue every year,” says Baird. He’s hopeful that if known carriers are not allowed to be used for breeding, the disease will become a thing of the past.

Also involved in this project are INSERM research associates Alexandra Charlesworth and Flavia Spirito and University of Guelph researchers Keith Linder and Prof. Julie Yager of the Department of Pathobiology.

Funding for this research was provided by the Ontario Ministry of Agriculture and Food, the Dystrophic Epidermal Bullosa Research Association and INSERM.