GBED
Glycogen Branching Enzyme Deficiency
recessive traitWhat is GBED?
GBED (Glycogen Branching Enzyme Deficiency) is a lethal recessive disease in which the horse's body cannot form normal glycogen. Without functional glycogen storage, foals lack the energy reserves required to sustain vital organs. Affected foals (G/G) are either stillborn, born weak and die within days, or are aborted mid-pregnancy. The condition is irreversible and always fatal — but carrier horses (N/G) are completely healthy and undetectable without testing.
How is it inherited?
GBED is autosomal recessive and always lethal in its homozygous form. Two carrier parents have a 25% chance of producing an affected foal. Because carrier horses show no signs, testing is the only way to know.
What do the results mean?
| Result | Status | What it means |
|---|---|---|
| N/N | Normal | No GBED alleles. Horse cannot produce affected offspring unless bred to a carrier. |
| N/G | Carrier | One normal and one GBED allele. Horse is completely healthy and unaffected. Will pass the allele to ~50% of offspring. |
| G/G | Affected (lethal) | Two GBED alleles. Foal cannot survive — death occurs in utero, at birth, or within the first days of life. This result is not seen in live adult horses. |
No GBED alleles. Horse cannot produce affected offspring unless bred to a carrier.
One normal and one GBED allele. Horse is completely healthy and unaffected. Will pass the allele to ~50% of offspring.
Two GBED alleles. Foal cannot survive — death occurs in utero, at birth, or within the first days of life. This result is not seen in live adult horses.
What should buyers know?
For buyers purchasing a horse to ride, GBED status makes no difference to the horse's health or performance — N/G carriers are fully healthy. For breeders, testing is critical to avoid unexpected foal loss from carrier-to-carrier pairings.
Which breeds are affected?
Seen in American Quarter Horses, Paints, Appaloosas, and related breeds. Estimated carrier frequency in the Quarter Horse population is around 7–10%.
This page is for general education only. Always consult a veterinarian or equine geneticist before making purchasing or breeding decisions based on genetic test results.
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