Phosphofructokinase (PFK) Deficiency

Phosphofructokinase (PFK) Deficiency

Phosphofructokinase Deficiency, commonly called PFK Deficiency (or sometimes less accurately called just "PFK"), is an inherited disorder where an essential enzyme, phosphofructokinase, is deficient. This enzyme, PFK for short, is critical in the conversion of glucose to energy, particularly in red blood cells and muscle cells. Dogs who are deficient in PFK will have muscle and red blood cells that cannot supply their own energy needs, which becomes most apparent in times of stress or heavy exercise. Much of the time, during levels of low stress and exercise, they will have a lower-than-normal level of red blood cells ("persistent mild anemia"), which may not be as readily apparent and may not exhibit any visible symptoms. It is in times of stress and exercise that the condition would become obvious and likely demand veterinary attention.

Symptoms of Phosphofructokinase Deficiency
Most of the symptoms would appear after stress, exercise, heat, or excessive barking, and they include tiredness, weakness, apparent muscle cramps, pale gums, and high fever. One symptom that is often the identifying factor of the disease is dark-colored urine, caused by the breakdown of blood products.

Inheritance of Phosphofructokinase Deficiency
Phosphofructokinase Deficiency is an autosomal recessive disease, meaning that, to be affected, a dog must inherit one copy of the mutated gene from each parent. Therefore, parents of an affected dog would be either affected themselves, or a carrier of the recessive gene. Carriers, while not showing clinical signs of PFK Deficiency, do in fact have a decreased level of PFK in the blood cells and muscle cells.

Breeds Affected by PFK Deficiency
Phosphofructokinase Deficiency has been found most prominently in the English Springer Spaniel, and less commonly in the English Cocker Spaniel and American Cocker Spaniel.

Diagnosis and Treatment
Mild persistent hemolytic anemia, a result of this condition, can be diagnosed by your vet. However, pinpointing PFK Deficiency as the cause of the anemia requires further testing. PFK levels can be measured by laboratory blood evaulation, but the definitive test is a genetic test which identifies the presence of the mutant genes. Additionally, the genetic test can determine if a dog is a carrier of the PKF Deficiency gene, which can help in responsible breeding decisions.

While there is no actual treatment for Phosphofructokinase Deficiency, it can be successfully managed to the point that affected dogs may have a relatively normal lifespan. The most important "treatment" is managing the dog's activity and stress levels, to prevent more severe anemia. In cases where anemia becomes critical, veterinary care is required to manage the condition until it normalizes.

Breeding Decisions
Dogs with Phosphofructokinase Deficiency, having both copies of the recessive gene, should never be bred and should be spayed or neutered. There is some debate in the dog community about breeding carrier dogs. The most conservative approach is to remove even carriers from breeding, in an effort to eliminate the gene from the population and thus improve the overall genetic health of the breed. If a carrier dog is bred, it is obviously critical that the mate be clear (not be a carrier, thus having no copies of the mutant gene). If a carrier is bred to a clear mate, then half of the offspring would be carriers, and future generations would require careful genetic screening to be aware of the carrier status. It is because of this long-term genetic responsibility that many breeders believe that eliminating even carriers from the breeding pool is the best approach.