GSD IIIa in Curly Coated Retrievers

Glycogen storage disease (GSD) is a recessively inherited metabolic disorder with deficient activity of enzyme or transport protein leading to abnormal structure of glycogen or its abnormal content in tissues. Clinical symptoms differ in dependence on the severity of the enzyme defect and on the tissues, where the enzyme is expressed. The Glycogen storage disease types are divided according to the enzyme defects and numbered chronologically according to the time of their description. In dogs, the following types of the Glycogen storage disease have been described so far:

• type Ia in Maltese dogs (lack of glucose-6-phosphatase; Von Gierke disease; OMIA 000418)
• type II in Lapland dogs (deficiency of lysosomal acid a-glukosidase, Pompe disease, OMIA 000419)
• type III in German shepherd (lack of glycogen debranching enzyme, Cori disease)
• type VII in English Springer Spaniel (deficiency of phosphofructokinase, Tarui disease, OMIA 000421)

• new type IIIa in Curly Coated Retrievers (deficiency of glycogen debranching enzyme)

In 2007, Brittany L. Gregory and Co. published a new discovered mutation c.4223delA in AGL-gene expressing the glycogen debranching enzyme and causing GSD IIIa in curly coated retriever. Deficiency of glycogen debranching enzyme causes storage of glycogen with abnormal compact structure.

Clinical signs of GSD IIIa in curly coated retrievers are mild in the first year of life. The abnormally structured glycogen is progressively stored in liver and muscles. The signs of the disease usually develop after the first year of life, the dogs are lethargic, show intolerance to exercises, episodic hypoglycemia and collapses occur. The storage in livers may lead progressively to cirrhosis, storage in muscles results in progressive muscle and hearth atrophy.

Mutations causing glycogen storage disease in Maltese dogs and English Springer Spaniels are known and can be tested. These tests have not been included in the offer of the Genomia laboratory so far.

The GSD IIIa is an autosomal recessive inherited disease. The disease develops in individuals, who inherit the mutated gene from both parents. These individuals are designated as P/P (positive / positive). Molecular-genetic tests can be used to confirm the diagnosis. The carriers of the mutated gene, designated N/ P (negative / positive, heterozygote carriers) obtained the mutated gene only from one parent and are without clinical signs; however they pass the disease on to their offsprings.

References:
Brittany L. Gregory et al.: Glycogen Storage Disease Type IIIa in Curly-Coated Retrievers; J Vet Intern Med 2007;21:40-46