If you're thinking of purchasing or adopting a Bengal kitten or adult, it is important to be aware of the health problems to which the cat may be prone. Ensure that the breeder you are purchasing from tests or screen their cats to prevent the transmission of certain inherited diseases. In this way, you will reduce or eliminate the chances of bringing an affected kitten home.
What is PK-def?
Erythrocyte pyruvate kinase deficiency or pyruvate kinase deficiency (as it is commonly known) is an inherited condition of the red blood cells, which causes anemia by chronic hemolysis (the destruction of red blood cells). This type of anemia is also called hemolytic anemia. PK-def was first described in humans in 1961, being the second most common red blood cell enzyme defect after glucose-6-phosphate dehydrogenase (g6pd) deficiency. (1)
In other words, if the enzyme pyruvate kinase is missing from the red blood cells (RBC/erythrocytes), then the RBC lifespan will decrease significantly, resulting in anemia (reduced erythrocyte count).
It is a rare condition in cats (as in humans) and can be found in Bengal, Abyssinian, Australian Mist, Domestic Shorthair and Longhair, Egyptian Mau, La Perm, Maine Coon, Norwegian Forest, Savannah, Siberian, Singapura, Somali, and Toyger cat breeds.
Because the cat's body quickly produces new red blood cells, the anemia is intermittent. Most of the time, this anemia is mild and occurs slowly, which allows the cat to get used to it and show variable clinical signs, which are not so obvious. The age at which PK-def occurs in Bengal cats is also variable and affects both sexes equally.
PK-def vs. PKD? Are they the same?
Pyruvate kinase deficiency is not the same as polycystic kidney disease (PKD), the latter being a genetic condition that affects the kidneys, causing chronic kidney disease. The cysts that grow in the kidneys will damage the tissue and enlarge the kidneys. All of these will eventually lead to chronic kidney failure or end-stage renal disease.
How and why PK-def occurs?
This condition has an autosomal recessive inheritance. Cats that have only one copy of the mutation (heterozygous) are called carriers. The ones that are affected have 2 copies of the mutation (one from each parent) and are called homozygous. They will transmit the disease to their offspring 100%.
Carrier cats, even if they show no clinical signs, can transmit the disease to 50% of their offspring if they are bred with a non-carrier cat.
If the carrier cat is reproduced with another carrier cat, their offspring will be: 25% free, 25% affected, and 50% carriers.
If a carrier cat is bred with an affected (homozygous) cat, their offspring will be: 50% carriers and 50% affected.
Homozygous cats, if they are reproduced with free cats, will have 100% carrier offspring.
If an affected cat is bred with another affected cat, their offspring will be 100% affected.
The bottom line is that it is important that carriers be detected before being bred in order not to transmit the mutation.
PK-def clinical signs
Studies suggest that PK-def manifestations in homozygous Bengal cats (splenomegaly, hemolytic anemia, and increased osmotic fragility of erythrocytes) are not actively reported because the disease may be episodic, mild, and subclinical. It is also suggested that additional factors would be needed to induce the disease, such as stress or activity level. (2)
Although there may be affected cats that show no obvious symptoms, most have mild to severe anemia, which can be progressive or intermittent.
Depending on the severity of the anemia, the following clinical signs may be seen: nausea, weakness, and lethargy – these modifications are due to the lack of red blood cells available to carry iron and oxygen in the body. Also, if blood clots develop, the cat may even be in pain.
If the anemia is severe, breathing may be impaired, jaundice, pale mucous membranes, enlarged spleen, tiredness, swollen abdomen, diarrhea, weight loss, and sometimes seizures may occur.
If the red blood cells are destroyed in a large number in a short time, the hemolytic crisis will occur and can be accompanied by fever, back or abdominal pain, and shock. It can endanger the cat's life.
As with other hereditary diseases in Bengal cats (HCM and PRA-b), there is no cure for PK-def. One medical procedure that could save the life of a cat in a hemolytic crisis is a blood transfusion, but it could also have adverse effects on the animal's body.
Another medical approach would be splenectomy (the surgical removal of the spleen), but it is a major procedure with a risk of death (Bengal cats are very sensitive to anesthesia, especially ketamine).
PK-def diagnosis
The differential diagnosis will be made between infection, feline infectious peritonitis (FIP), feline immunodeficiency virus (IVF), feline leukemia virus (FeLV), Mycoplasma haemofelis, certain immune deficiencies, or toxins. All of these can have anemia as a clinical sign. If all of them are ruled out, then the cat will be tested for PK-def by molecular genetic testing, which identifies both affected and carrier animals.
The diagnosis of anemia can be made by hematological tests, which can identify the concentration and number of red blood cells.
What are the recommendations for testing and reproduction?
Bengal cats that are tested positive for PK-def will not be reproduced. It is also recommended that those who do not show symptoms should be tested beforehand because they may be carriers.
The most popular laboratory for genetic testing in Bengal cats in Australia is represented by UC Davis Veterinary Genetics Laboratory. They test for HCM, PRA-b, and PK-def, among others.
A DNA test result for PK-def in Bengal cats from UC Davis Laboratory will look like this:
Cats with N/N genotype will not have PK deficiency.
Cats with N/K genotype will not have PK deficiency, but are carriers. They will transmit this PK deficiency variant to 50% of their offspring.
Cats with K/K genotype will have PK deficiency; severity of symptoms cannot be predicted and may be variable.
- Negative or normal cats cannot transmit the pyruvate kinase deficiency variant to their offspring, and they will be reproduced only with PK-def-free partners.
- Cats that have only one mutation are carriers (they do not develop the disease) and they will not be reproduced. Breeding two carrier cats is predicted to produce 25% normal, 25% affected, and 50% carriers. Breeding them with a non-carrier cat can transmit the disease to 50% of their offspring.
- Cats that have both mutations suffer from PK-def and will not be reproduced.
An example Test Report is shown below
References
- Pyruvate kinase deficiency. Association with G6PD deficiency. (1992). BMJ (Clinical research ed.), 305(6856), 760–762. https://doi.org/10.1136/bmj.305.6856.760
- Grahn, R. A., Grahn, J. C., Penedo, M. C., Helps, C. R., & Lyons, L. A. (2012). Erythrocyte pyruvate kinase deficiency mutation identified in multiple breeds of domestic cats. BMC veterinary research, 8, 207. https://doi.org/10.1186/1746-6148-8-207
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