Breeds Affected: Quarter Horse and related breeds
Samples Accepted: Blood, Hair
Disease Information: Glycogen Storage Disease IV (GSD IV) is also known as Glycogen branching enzyme deficiency (GBED). This disease is always fatal, as affected animals are unable to properly store glycogen. Fetuses may be spontaneously aborted, foals may die shortly after birth, or by 6 months of age.
Inheritance Information: GSD IV is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The horse is normal, and cannot produce GSD IV-affected offspring.
N/gbed The horse is a carrier of GSD IV, and can pass the allele on to approximately 50% of any offspring. If bred to another N/gbed carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
gbed/gbed The horse is affected with GSD IV. This disease is fatal, and affected horses do 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.
Test Information: This test is based on a single base pair change in exon 1 of the GBE1 gene.
Ward TL, Valberg SJ, Adelson DL, Abbey CA, Binns MM, and Mickelson JR. (2004). Glycogen branching enzyme (GBE1) mutation causing equine glycogen storage disease IV. Mamm Genome 15, 570-577.
Further information is available at the Online Mendelian Inheritance in Animals website.