Glycogen Storage Disease IIIA (Curly Coat Retriever Type)

Test Overview:

This is an autosomal recessive disease of curly coated retrievers.  A genetic mutation leads to a deficiency in the glycogen debranching enzyme (GDE) in liver and muscle.  Glycogen is how glucose is stored for later use when it is needed, but this use is dependent on GDE cleaving glucose molecules from stored glycogen.  When this cannot occur glycogen accumulates in tissues, leading to organ damage over time.  In addition, signs due to a lack of blood glucose can be seen intermittently. The first indication of this condition in an affected dog is an elevation in hepatic enzymes (i.e. ALT, AST, ALP) in the blood.  In addition the muscle enzyme CPK (or CK) may be intermittently elevated before 12 months of age, after which several studies have shown it increases more reliably.  Clinical signs are not usually seen in the first year of life, but sometime in the second year of life dogs develop lethargy, reduced exercise tolerance and intermittent hypoglycaemic collapse which is rapidly reversible by the administration of glucose preparations. Glycogen accumulates steadily in liver cells and muscle cells, including in the heart.  The liver becomes affected by fibrosis, then cirrhosis.  Muscle contractile apparatus is disrupted by the large glycogen deposits, and becomes frayed.  Eventually muscle contractile units are replaced by fibrous tissue.  Ventricular enlargement (due to myopathy in the heart) is commonly documented in humans with glycogen storage disease type IIIa, however the incidence of related cardiomyopathy in curly coated retrievers is not known. There is no cure for this disease.  Prevention can be accomplished by testing all breeding animals and avoiding the breeding of a carrier or affected animal.  If a carrier has a special benefit to the genetic pool of the breed otherwise, that dog may be bred to a clear animal only, and all progeny tested.  Only clear pups should then be used for breeding.