Glycogen Branching Enzyme Deficiency (GBED)
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 to glycogen. This inherited disorder prevents the body from producing the enzyme needed to branch the glycogen structure, preventing 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 which are affected by GBED suffer from a range of symptoms associated with this lack of fuel, 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 foetus 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 Horse, 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.
The mutation which causes this disease, has been identified by Dr. Stephanie Valberg and Dr. James Mickelson of the University of Minnesota, and is licensed for diagnostic use by Animal Genetics Inc (USA).
Quarter Horse, any horse with quarter horse blood.
Additional Tests For Quarter Horses:
Animal Genetics offers DNA testing for Glycogen Branching Enzyme Deficiency (GBED). The genetic test verifies the presence of the recessive GBED gene and presents results as one of the following:
|Gb/Gb||Affected||The horse carries two copies of the GBED mutation and is homozygous for GBED. The horse is affected with the GBED genetic disorder.|
|n/Gb||Carrier||Both the normal and mutant copies of the gene detected. Horse is a carrier for the GBED mutation, and can pass on a copy of the defective gene to its offspring 50% 0f the time.|
|n/n||Negative||Horse tested negative for the gene mutation that causes GBED and will not pass on the defective gene to its offspring.|