Glycogen Branching Enzyme Deficiency (GBED)

Glycogen Branching Enzyme Deficiency

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Breeds: American Indian, Appaloosa, Appaloosa Cross, Appaloosa/Friesian, Appaloosa/Quarter Horse, Appaloosa/Thoroughbred, Appendix, AraAppaloosa, Arabian/Paint, Arabian/Quarter Horse, Australian Stock Horse, Azteca, Baroque Pinto, Canadian, Cleveland Bay, Clydesdale/Paint Cross, Colonial Spanish Horse, Crossbred, Grade Horse, Grade Pony, Miniature Appaloosa, Mixed Breed, Mixed Breed (Horse), Morgan Horse, Origine Constatée, Paint Cross, Paint Horse, Paint Horse/Thoroughbred, Paint/Warmblood, Percheron Cross, Ponies of America, Pura Raza Espanola, Quarter Cross, Quarter Horse, Quarter Pony, Quarter/Paint Horse, Quarter/Stock Horse, Quarter/Thoroughbred, Quarter/Warmblood, Spanish Barb, Spanish Mustang, Stock Horse, Stonewall Sporthorse, Sugarbush Harlequin Draft, Thoroughbred, Unspecified, Welsh Mountain/Quarter Horse


Glycogen Branching Enzyme Deficiency (GBED) is a fatal condition caused by the bodies' inability to properly store sugar. In a normal horse, the body stores sugar as energy by converting glucose (a type of sugar) to glycogen (storable energy). This inherited disorder prevents the body from producing the enzyme needed to create the glycogen structure. This prevents the horse from being able to adequately store the sugars. This means that the horse will not be able to store enough energy to fuel important organs, such as the muscles and brain.

Foals born with GBED suffer from a range of symptoms associated with this lack of energy storage, such as low energy, weakness, and difficulty rising. Other symptoms include low body temperature, contracted muscles, seizures, and sudden death. Unfortunately, GBED is always fatal; most affected foals will die before the age of 8 weeks. GBED often causes the fetus to be aborted in utero. Research suggests that as many as 3% of aborted Quarter Horse foals were homozygous for the GBED mutation.

Studies show that the mutation responsible for GBED is carried by as many as 10% of Quarter Horses, Paint Horse breeds and related breeds. GBED is an autosomal recessive trait, meaning a foal can only be affected if the foal inherits the disease from both parents. Horses that are carriers of the GBED have one copy of the mutation but do not have any symptoms associated with the disorder. This makes DNA testing important to screen for carriers and prevent this fatal condition. If two carriers are bred together, there is a 25% chance per foal that they will develop GBED.

The mutation which causes this disease has been identified by Dr. Stephanie Valberg and Dr. James Mickelson of the University of Minnesota. Animal Genetics Inc. (USA) is licensed for diagnostic testing of GBED.

Possible Results

Genotype Description
Gb/Gb Affected: Horse has two copies of the GBED gene mutation and will exhibit signs of the disorder.
N/Gb Carrier: Horse has one copy of the GBED gene mutation. Horse has a chance to pass this gene on to any offspring.
N/N Clear: Horse is negative for the GBED gene mutation.