Glycogen branching enzyme deficiency

Veterinary advice should be sought before applying any treatment or vaccine.

Glycogen Branching Enzyme Deficiency

Glycogen branching enzyme deficiency (GBED) is a fatal, autosomal-recessive disease that occurs in newborn Quarter horse, Paint horse, and related breeds' foals. It is caused by Y34X missense mutation at codon 34 in exon 1 of the glycogen branching enzyme 1 (GBE1) gene. The foals lack the enzyme necessary to store glycogen (sugars) in its branched form and therefore cannot store sugar molecules. The foal is born lacking the enzyme necessary for storing glycogen and the horse's brain, heart muscle, and skeletal muscles cannot function, leading to rapid death.

It is estimated that 8% of Quarter Horses and Paint Horses are carriers of the mutation. Since the gene is recessive, a horse can carry the gene and pass it to its offspring unknowingly. GBED is related to Glycogen storage disease type IV in humans.


Abortion or still birth
Low body temperature at birth
Increased respiratory rate
Muscle weakness
Contracted tendons in all four legs of foal
Sudden death on pasture of foals


  • History
  • Clinical signs
  • Physical exam
  • Genetic Testing



There is no effective treatment, all known cases have been fatal; foals aborted, stillborn, die shortly after death, or euthanized due to weakness.



Scientific Research

General Overviews

Age Range

GBED causes mares to have late-term abortion or death of foals by a few months of age.

Commonly Affected Breeds

Quarter Horse iconPaint Horse icon