GBED Glycogen Branching Enzyme Deficiency

Sample

• 30 to 40 - hair roots - envelope

• 5 mL - blood - K3 EDTA tube

Turnaround time

• 2 to 5  working days

Why test?

• This DNA test identify inapparent carriers of the GBED fatal disorder. 

• In breeding selection is recommended to avoid the crossbreeding of two GBED inapparent carriers to prevent in utero abortion of foetus and the birth of foals affected by GBED. 

• To confirm GBED in affected foals.

DNA testing provide important tools for informed choices about breeding selections to prevent abortion and the birth of affected foals.

 Frequency and affected breeds

• More frequent in Paint Horses and Quarter horses related breeds.
  
• A prevalence of  7,1% and 8,3% in the Paint and Quarter Horse breeds, respectively (Wagner et al., 2006).
  

Results description

The DNA test verifies the presence of the recessive GBED alleles and presents results as one of the following: 

• N/ - Negative for GBED. Absence of the defective allele responsible for GBED.

• GBED/N - Carrier - Positive heterozygous for GBED. Presence of one copy of the allele responsible for GBED.  The horse is a carrier for GBED and can pass on a copy of GBED allele to their progeny when bred.

• GBED/ - Affected - Positive Homozygous for GBED. Presence of two copies of the allele responsible for GBED.  The animal is affected by GBED disorder. GBED is lethal causing abortion and/or  neonatal mortality.

Additional information

Glycogen Branching Enzyme Deficiency (GBED) fatal condition caused by an autosomal recessive genetic disorder that results in the bodies' inability to properly store sugar in the glycogen form.

In a normal horse, the body stores sugar as energy by converting glucose to glycogen.

This genetic disorder  affects the production of the enzyme needed to branch the glycogen structure, preventing the horse from being able to adequately store sugar in the glycogen form. This means that the horse will not be able to store enough energy to fuel important organs, such as the muscles and brain.

Unfortunately, GBED is always fatal. 

GBED often causes the foetus to be aborted in utero. When born most affected foals will die in the first weeks of age. 

Research studies showed that as many as 2,5% of aborted Quarter Horse foetus were homozygous for the GBED mutation (Wagner et al., 2006). 

Foals born which are affected by GBED suffer from a range of clinical signs associated with this lack of sugar, such as low energy, weakness and difficulty rising.  Other clinical signs include low body temperature, contracted muscles, seizures, and sudden death.

REFERENCES

Tryon RC, Penedo MC, McCue ME, Valberg SJ, Mickelson JR, Famula TR, Wagner ML, Jackson M, Hamilton MJ, Nooteboom S, Bannasch DL. Evaluation of allele frequencies of inherited disease genes in subgroups of American Quarter Horses. J Am Vet Med Assoc. 2009 Jan 1;234(1):120-5. doi: 10.2460/javma.234.1.120. PubMed PMID: 19119976.DOI: 10.2460/javma.234.1.120

Wagner ML, Valberg SJ, Ames EG, Bauer MM, Wiseman JA, Penedo MC, Kinde H, Abbitt B, Mickelson JR. Allele frequency and likely impact of the glycogen branching enzyme deficiency gene in Quarter Horse and Paint Horse populations. J Vet Intern Med. 2006 Sep-Oct;20(5):1207-11. PubMed PMID: 17063718.DOI: 10.1892/0891-6640(2006)20[1207:afalio]2.0.co;2