Glycogen Storage Disease IV (GSD IV Horse)

• Weakness
• Low body temperature
• Accelerated breathing
• Tremors
• Spontaneous abortions

• In glycogen branching enzyme deficiency (GBED), glucose cannot be stored in the form of glycogen.
• This leads to a lack of energy for muscles and organs.
• Foals may die shortly after birth (within the first 8 weeks) due to organ failure (liver or heart).

This test detects a single basepair change in exon 1 of the GBE1 gene.

Inheritance: autosomal recessive

→ Only horses with two copies of the variant (gbed/gbed) are affected. Horses with only one copy (N/gbed) are clinically healthy carriers.

Genotype

N/N = normal

The horse has no copies of the genetic variant causitive for GBED/GSD IV and therefore cannot pass it on to its offspring.

N/gbed= a carrier

The horse is clinically healthy.  It has one copy of the genetic variant causitive for GBED/GSD IV, which will be passed on to its offspring with a probability of 50%.

gbed/gbed= affected

The horse is affected and will not live long enough to reproduce.

• Carriers may be bred to normal animals (N/gbed x N/N) without any risk of producing affected offspring. The offspring should also be tested before breeding to determine if they are carriers or normal.
• Breeding two carriers (N/gbed x N/gbed) is not recommended due to the possibility of 25% of the offspring being affected.

Ward, TL., Valberg, SJ., Adelson, DL., Abbey, CA., Binns, MM., Mickelson, JR.: Glycogen branching enzyme (GBE1) mutation causing equine glycogen storage disease IV. Mamm Genome 15:570-7, 2004. Pubmed reference: 15366377.

Further information is available at Online Mendelian Inheritance in Animals.