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GBED is a disorder that prevents the storage of glycogen in muscles and other tissues, causing late term abortion, stillbirths and death in affected foals

Full name

Glycogen branching enzyme deficiency

Breeds known to be affected

Quarter Horse and related breeds

Inheritance pattern

Autosomal recessive


GBED is a lethal storage myopathy caused by a mutation in the GBE1 gene that prevents the animal from properly storing glucose. The horse will eventually run out of stored energy, which will damage its organs. The symptoms observed are associated with the lack of energy preventing the organs from working correctly, and may include general weakness, failure to thrive, low body temperature, seizures and difficulty rising.

GBED is always fatal, with most affected foals dying before the age of 8 weeks. GBED can also cause foetuses to be aborted or born prematurely. It is inherited as a recessive trait, so only homozygous (GBED/GBED) horses are affected. If a horse is a carrier (n/GBED), it will not show any clinical signs of GBED. However, there is a 50% chance it will pass the variant to its offspring, so mating to other carriers should be avoided to prevent the birth of an affected foal.

Interpretation of results

n/n: Horse does not carry the mutation associated with GBED.

n/GBED: Horse has one copy of the mutation associated with GBED.

GBED/GBED: Horse has two copies of the mutation associated with GBED.


Ward et al. Glycogen branching enzyme (GBE1) mutation causing equine glycogen storage disease IV. Mammalian Genome 2004;15:570-577 doi:10.1007/s00335-004-2369-1.

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