Belgian JEB Carrier Rate Steady; Mare Testing To Be Required

Belgian JEB Carrier Rate Steady; Mare Testing To Be Required

Belgian neonates with JEB have large lesions on the body that appear as if the skin is missing.

Photo: Courtesy Dr. J.D. Baird

Breed registry officials have taken steps over the last decade to reduce the number of Belgian foals born with a fatal skin disorder called junctional epidermolysis bullosa (JEB). And while veterinarians report anecdotally that they’re seeing fewer cases, a new analysis of mandatory sire screening results has spurred the registries to expand testing requirements.

John D. Baird, BVSc, PhD, professor emeritus of the University of Guelph’s Ontario Veterinary College, worked with researchers at the University of California (UC), Davis, Veterinary Genetics Laboratory to examine 10 years of data from both the Belgian Draft Horse Corporation of America (BDHCA) and the Canadian Belgian Horse Association (CBHA). He presented the team’s results at the 2013 American Association of Equine Practitioners’ Convention, held Dec. 7-11 in Nashville, Tenn.

Junctional epidermolysis bullosa is one of a large group of inherited diseases that result from a failure to produce a protein essential for skin layer adhesion. Affected foals are “characterized clinically by a fragile skin that results in ulcers and erosions following minor trauma,” he said. These diseases are named for where the level of separation takes place in the skin. Epidermolysis bullosa can occur in a variety of species, but Belgian horses experience a particular type at the level between the epidermis (outer layer of the skin) and the dermis, which is immediately beneath the epidermis. Often called “hairless foals,” Belgian neonates with JEB have large lesions on the body that appear as if the skin is missing. Baird noted that a similar condition occurs in Saddlebred foals, but it involves a different mutation in a different gene.

He said owners might notice a blood-tinged discharge coming from an affected newborn foal’s mouth. Inside the mouth they’ll often discover blisters and ulcers as the source of the blood. Foals with JEB also have incisor teeth visible at birth (normally, a newborn foal has no teeth) that are serrated from enamel erosion. Owners usually first notice the skin lesions over the joints and where there is contact pressure (mainly on areas where their skin makes contact with the ground when they lie down, such as over fetlock joints, hock joints, and even on head where there is contact with the ground on lying in a stall or on the ground). Lesions on the foals’ legs often extend all the way down to the feet. Human researchers have suggested that leg rubbing in utero could be the cause of these lesions that might be present at birth. Some foals with JEB will lose one or more hooves due to absence of the protein.

In 2001 French human researchers identified in JEB-affected foals a mutation in a gene (LAMC2) that encodes the skin adhesion protein laminin-332. The function of laminin-332 is to provide stable anchorage of the epidermis to the underlying dermal cells. They also established an autosomal recessive mode of inheritance, which means the foal must be homozygous—carrying two copies of the defective LAMC2 gene, one from each parent—to develop JEB. Scientists at UC Davis developed a polymerase chain reaction test (a kind of DNA test) that would detect carriers, and the BDHCA and CBHA put sire testing requirements in place in November 2002 and January 2003, respectively, for new foal registrations.

What They Found

Baird said the aim of the testing requirements was and is to prevent the birth of JEB foals and reduce the number of carriers in the breed. “Tests are done through (the) corporation office,” he said, “with all fees paid in advance. JEB testing of mares is voluntary, except when mares are bred by artificial insemination with frozen semen.”

For the two Belgian herd books, the UC Davis team tested mane hair root samplesfrom 2,554 horses for JEB from November 1, 2002, to December 31, 2012. Findings included:

  • 319 (12.5%) were carriers, which breaks down as 206 (11.5%) of the 1,785 tested for BDCHA, and 47 (12%) of 391 tested for CBHA;
  • In both registries, only 336 mares have been tested, with 65 (17.8%) identified as carriers;
  • In the past three years, of the 42 carriers identified in the BDHCA registry, 21 (50%) were sired by noncarrier stallions and out of mares that had not been JEB-tested; and
  • In 2012, of 132 horses that were JEB-tested, 12 (10 stallions and two mares) were identified as carriers. Of the horses JEB-tested, 100 (75.8%) were sired by noncarrier stallions, 30 (22.7%) were sired by stallions born before mandatory testing was required, and two were sired by one known carrier stallion.

“There have been variations in numbers tested over the years,” Baird said. “It’s disappointing the low number of mares tested. The registries charge less for mare testing because they’re trying to encourage mares to be tested, but people are still relying on the stallion testing” to reduce their chance of having a JEB-affected foal.

While Baird and the research team did not see a statistically significant trend of decline in carrier numbers over the 10 years of testing, “the good news is that, in 2012 of a total of 608 male registrations, 83% (504) were sired by noncarrier stallions,” he noted. “Anecdotally, I cannot prove it, but I know that less of these animals have foals with JEB,” he said. “We don’t hear much of the condition anymore. Most people are now using noncarrier stallions, however the bad news is that only 4% of broodmares are being JEB tested. Many of the carriers that are now being detected are getting the mutation from their nontested dams.”

He reported that in response to the findings, the BDHCA will introduce mandatory JEB and DNA testing of breeding-age mares, which will begin Jan. 1, 2015. “When both the sire and dam have been tested as noncarriers, the resulting foals will be recognized by the registry as noncarriers and will only need DNA testing to verify their parentage,” he said. “This will result in considerable financial saving to the breeders.”

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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