Glycogen branching enzyme deficiency (GBED) is a fatal disease of newborn Quarter Horse and Paint foals. GBED is an inherited disease with autosomal recessive pattern of inheritance. It has been estimated that 8.3% of Quarter Horses and 7.1% of Paints are carriers of the gene for GBED. The enzyme deficiency will often result in abortions, still-births, and the birth of weak foals.
This enzyme is necessary to create a compact, highly-branched, energy-dense, bioavailable glycogen molecule. The foetus and newborn foal are highly dependent on a continual supply of glucose, which can be sourced from mare’s milk, liver glycogen, or storage depots in tissues. Affected foals are unable to store glycogen in this efficient branched form and therefore at risk for energy (glucose) depletion in brain, heart and skeletal muscle.
In GBED neonatal foals there are a variety of clinical signs. These include a low body temperature, flexural limb deformities, persistent recumbency, seizures, and respiratory and cardiac failure. The foals are hypoglycaemic. Often the signs are confused with systemic sepsis or birth-related asphyxia. The condition is always fatal, although some foals have survived several months.
The specific mutation in the gene that encodes the enzyme has been identified, and consequently a genetic test has been developed. Hair samples with attached roots are sent to accredited laboratories for testing.
The diagnosis is confirmed by this test, but is suspected in Quarter Horse or American Paint foals with consistent signs. Affected foals typically have low blood glucose, elevated muscle enzymes (AST, CK) and GGT.
Tags: Foals, Musculoskeletal