Researchers at UM find gene that causes death

ST. PAUL, MINN.—Researchers discovered the gene responsible for glycogen branching enzyme deficiency (GBED), which kill about one-fourth of foals born to carriers of the faulty make-up.

Stephanie Valberg, DVM, PhD, led the research team at the University of Minnesota (UM) in identifying the GBE1 gene, which encodes the glycogen branching enzyme (GBE) involved in glycogen synthesis.

Dr. Stephanie Valberg visits a mother, Shena, and her new foal at the University of Minnesota&s College of Veterinary Medicine barn. Valberg is conducting several tests on neuromuscular issues in large animals.

Veterinary medicine researchers have been working to discover the cause of early death in foals for the past five years, but GBE1 has been difficult to pinpoint.

GBED occurs when horses that carry the recessive gene breed with another carrier, says Dr. Jim Mickelson, UM researcher and professor of veterinary bioscience. Quarterhorses and similar breeds run the greatest risk of carrying the defective GBE1 gene, but mixed breeds also run the risk of passing on the trait to their offspring.

The foal's deficiency is camouflaged by symptoms that resemble other equine neonatal diseases. Breeders often determine that foals' deaths are caused naturally instead of considering genetics as a probable cause, Mickelson says.

Foals that are born weak can die very soon after birth, or they can be nursed into health in the hospital, Valberg says.

"The foals seem to get stronger for a while and then die very suddenly," Valberg adds. "Other foals have spent much more time in the hospital and have progressively gotten weaker to the point where they can no longer stand up."

Weak foals lacked an enzyme required to form glycogen, the glycogen branching enzyme. Without glucose to metabolize energy, the foals were unable to survive more than two months.

"If owners of the majority of Quarterhorses have a planned breeding program to avoid carriers, the defective gene will eventually die out," says Valberg.

The discovery of the gene led to a new test that can screen horses for the trait before they are bred.

For $35 per horse, stallions and mares can be tested, sparing emotional and economic loss by a foal carrying the defective trait.

Blood samples, as well as mane or tail samples with intact roots, can be used for the test, Valberg says.

Ten percent of all Quarterhorses in the United States are carriers of the defective gene, Mickelson says. Approximately 50,000 horses a year could be affected by the gene, Mickelson adds.

"More than 300 tests have already been conducted," Valberg says.

The study was funded through the American Quarter Horse Association and the University of Minnesota Equine Center with funds provided by the Minnesota Racing Commission.

Editor’s Note: For more information, visit acadmec-server.cvm,umn.edu/neuromuscularlab/home.html