Glycogenosis type IIIa (GSD IIIa), an autosomal recessive metabolic disease due to deficiency of the glycogen debranching enzyme (amylo-1,6-glucosidase) caused by a mutation in AGL. Abnormal glycogen accumulates in liver and muscle, with exercise intolerance, lethargy and collapse, and progressive elevation of liver and muscle enzymes. In the Curly Coated Retriever the course is milder than in the German Shepherd.

Documented in the Curly Coated Retriever (United States, New Zealand, Australia and Finland). No broad population estimates of carrier frequency are available (limited data).

- Episodic exercise intolerance and collapse after exercise
- Lethargy
- Muscle weakness
- Elevation of ALT, ALP, AST and CK from the first year of life
- Hepatomegaly with progressive hepatic fibrosis
- Hypoglycaemia under stress
- Signs apparent at around 14 months of age

GSD IIIa in the Curly Coated Retriever was characterised by Gregory et al. (2007), who identified the causal deletion of an adenosine in the AGL gene and developed the carrier test. Yi et al. (2012) described the phenotype in detail in a colony segregating the mutation, confirming progressive hepatic fibrosis and muscle damage.

- Genotype breeding dogs before mating.
- Do not mate two carriers (25 % affected homozygotes).
- If a carrier is mated, do so only with a clear homozygote.
- Do not breed affected animals.
- Test parents and siblings of affected animals, since the parents of an affected dog are obligate carriers.

The diagnosis is confirmed by enzyme activity (debranching) in liver/muscle and by genotyping. Monitor liver and muscle enzymes and blood glucose in affected animals. The disease of the Curly Coated Retriever is milder than that described in the German Shepherd, probably due to differences in mutation or genetic background; the prognosis includes progressive hepatic fibrosis.

1. Gregory BL et al. 2007. Glycogen storage disease type IIIa in curly-coated retrievers. Journal of Veterinary Internal Medicine. PMID: 17338148
2. Yi H et al. 2012. Characterization of a canine model of glycogen storage disease type IIIa. Disease Models & Mechanisms. PMID: 22736456
3. OMIA:001577-9615. Glycogen storage disease IIIa in Canis lupus familiaris. Online Mendelian Inheritance in Animals.