Glycogen storage disease VII, PFK deficiency is an inherited metabolic disorder affecting several breeds of dog. Glycogen is the primary source of energy for the body. Affected dogs have insufficient activity of the phosphofructokinase Enzyme which breaks down glycogen for energy. Deficiency of this enzyme results primarily in easily damaged red blood cells (hemolysis) and less severe damage to skeletal muscle cells. Affected dogs can have pale gums from decreased numbers of red blood cells (Anemia) and may be lethargic or unwilling to exercise. After strenuous activity or periods of excitement or stress, affected dogs may have symptoms of hemolysis and muscle cell damage, which can include red or brown urine, muscle cramping and jaundice. Affected dogs generally have a normal life expectancy, but may have recurrent episodes of hemolysis after exercise and muscle wasting progressing to an inability to walk.
Breed-Specific Information for the English Cocker Spaniel
The English Cocker Spaniel is included as a breed susceptible to glycogen storage disease VII, PFK deficiency because of its close relatedness to the Cocker Spaniel, which is known to develop this disease due to Mutation of the PFKM gene. The frequency of the causal mutation in the general English Cocker Spaniel population is unknown.
Genetic testing of the PFKM gene in English Cocker Spaniels will reliably determine whether a dog is a genetic Carrier of glycogen storage disease VII, PFK deficiency. Glycogen storage disease VII, PFK deficiency is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the PFKM gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. English Cocker Spaniels that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
Gerber K, Harvey JW, D’Agorne S, Wood J, Giger U. Hemolysis, myopathy, and cardiac disease associated with hereditary phosphofructokinase deficiency in two Whippets. Vet Clin Pathol. 2009 Mar;38(1):46-51.
Skibild E, Dahlgaard K, Rajpurohit Y, Smith BF, Giger U. Haemolytic anaemia and exercise intolerance due to phosphofructokinase deficiency in related springer spaniels. J Sm Anim Pract. 2001;42:298-300. [Not in PubMed]