Missing enzymes can lead to foal deaths

Missing enzymes can lead to foal deaths

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Apr 01, 2002

A new genetic disease is selectively killing certain Quarter Horse foals by 2 months of age, report researchers at the University of Minnesota (UM).

The foals were lacking an enzyme required to form glycogen, the glycogen branching enzyme (GBE). Without the necessary glucose to metabolize energy, the newborn foals were unable to survive.

UM College of Veterinary Medicine researchers, led by Stephanie Valberg, DVM, Ph.D., analyzed seven related foals that died by 7 weeks of age and extracted tissue samples from their mothers, half and full siblings to study glycogen formation and two enzymes in its synthesis.

"We think (the foals) have a defect in the gene that is responsible for producing the (GBE) enzyme so they don't produce normal protein and therefore (the gene) doesn't work properly," says Valberg.

Findings indicate that GBE deficiency may be a common cause of neonatal mortality in Quarter Horses, but the deficiency is camouflaged by clinical signs that resemble other equine neonatal diseases.

They can present a whole range of different signs, says Valberg.

"Sometimes they're born weak and die very soon after birth. Sometimes they're born weak and can be nursed into health in the hospital. They seem to get stronger for awhile and then die very suddenly," she explains.

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.

Most of the foals Valberg has seen didn't live beyond 10 weeks of age.

At this time, Valberg says researchers don't know how many foals are afflicted annually with the deficiency.

Plans are to develop a genetic test to identify affected foals with a blood test and identify the horses that might carry this disease.

Valberg recommends veterinarians advise owners if they have a foal that has GBE deficiency to be aware that if they breed the mare again back to the same stallion, they have a one in four chance of getting this disease again.

The research will be published in the Journal of Veterinary Internal Medicine.