BASICS
- This is an inherited autosomal recessive genetic disease of Quarter Horses and related crosses that results in a nonsense mutation in the gene coding for GBE, rendering the enzyme ineffective
- Also known as glycogen storage disease IV, which is also reported in humans and Norwegian forest cats
- GBE is needed for the formation of the 1,6 branch points in glycogen. This defect in glycogen can lead to abnormal glucose homeostasis in cardiac and skeletal muscle and liver
- Foals typically exhibit weakness and hypotonia and die shortly after birth
- Quarter Horse and Paint neonatal foals
- Clinical signs are generally seen from the time of birth
- Late term abortion in mares carrying an affected fetus
- Many affected foals present for other illness such as septicemia. Concurrent disease such as pneumonia is common in this age group of foals
- Late-term abortion (up to 3% of all abortions in Quarter Horses)
- Stillbirths or persistent recumbency
- Transient flexural limb deformities
- Seizures—due to inadequate glucose metabolism in neurons
- Cardiorespiratory failure—due to muscular weakness and cardiomyopathy
- Heritable trait among certain Quarter Horse and Paint lines
- Defective gene is on chromosome 26, which encodes the GBE
- In 2004, the genetic basis of the defective GBE gene was identified by cDNA sequences—a single C-to-A substitution at base 102 of codon 34 of exon 1
- When evaluated in 11 affected foals, all were homozygous for the defective X34 allele. When the gene is expressed, the mRNA product encodes for a 699 amino acid protein with a nonsense mutation, rendering the GBE ineffective. The affected foal pedigrees had a common ancestry and contained prolific stallions who are likely to be heterozygous for the recessive X34 allele
- Up to 10% of all Quarter Horses may have at least 1 defective gene
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS