Glycogen storage disease VII (GSD VII) in German Spaniels

Glycogen storage disease (GSD) is an inherited metabolic disorder resulting from the deficiency of activity of individual enzymes or transport protein that leads to either abnormal glycogen structure or abnormal tissue glycogen content. Clinical symptoms vary depending on the severity of the enzyme defect and on the tissues in which the enzyme is expressed. Glycogen storage diseases are classified according to the enzyme defect and numbered chronologically, according to the time of their mapping.

Type VII glycogenosis occurs in the German Spaniels and is caused by a missense mutation c.550C>T in the gene for the muscle-type enzyme phosphofructokinase (PFKM). Insufficient activity of the phosphofructokinase enzyme results primarily in easily damaged red blood cells (haemolysis) and exertional myopathy. Clinical symptoms include muscle cramps and intolerance to physical activity. During haemolytic crisis, the dog may develop severe anaemia, icterus, fever, lethargy, and anorexia.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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References:

Inal Gultekin, G., Raj, K., Lehman, S., Hillström, A., Giger, U. : Missense mutation in PFKM associated with muscle-type phosphofructokinase deficiency in the Wachtelhund dog. Mol Cell Probes 26:243-7, 2012. Pubmed reference: 22446493