PK Deficiency in Beagles

The deficiency of pyruvate kinase (PK Def.) is caused by inherited hemolytic disease that occurs not only in dogs, but also in humans and cats.

Pyruvate kinase is a key regulatory enzyme in anaerobic glycolysis.  The deficiency of this enzyme causes insufficient production of ATP, which results in erythrocyte lysis or their premature destruction in the spleen. The increased destruction of erythrocytes expresses itself clinically as anaemia. The life-span of erythrocytes in dogs is approximately one month; in case of PK deficiency is the life-span of erythrocytes only several days. The PK deficiency is accompanied by general weakness, increased heart rate, very pale mucous membranes (gums), liver function disorder, hepatomegaly, splenomegaly, exercise intolerance and loss of weight.

The first clinical signs usually occur approximately at 4 months of age of the affected dog.  The heterozygous dogs (carriers of the mutation) are usually asymptomatic, although they have half the normal level of pyruvate kinase activity. Affected physically inactive dogs show later onset of clinical signs.

The hematologic analysis usually discovers severe anaemia and high concentration of ferritin level in the serum. Some dogs develop other symptoms such as severe secondary hemochromatosis, progressive myelofibrosis and osteosclerosis of bone marrow.

As the clinical sign can be easily confused with other metabolic disorders, the testing of the responsible mutations in dog breeds is a suitable solution for determination of a correct diagnosis caused by the pyruvate kinase deficiency.

The casual mutation in PK-LR gene was first described in Basenji breed (Whitney 1995). Later, casual mutations have also been found in other dog breeds such as Labrador Retriever (c.799C>T), Pug dogs (c.848T>C), Beagles (c. 994G>A), Cairn Terrier and West Highland White Terrier (6 bp insertion in exon 10) (Gultekin 2012).

PK Def is an autosomal recessive disorder. The disease affects dogs with P/P (positive / positive) genotype only. Dogs with P/N (positive /negative) genotype are clinically without any symptoms. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

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References:

Gultekin, G.I., Raj, K., Foureman, P., Lehman, S., Manhart, K., Abdulmalik, O., Giger, U.: Erythrocytic pyruvate kinase mutations causing hemolytic anemia, osteosclerosis, and seconday hemochromatosis in dogs. J Vet Intern Med 26:935-44, 2012. Pubmed reference: 22805166. DOI: 10.1111/j.1939-1676.2012.00958.x.

Whitney, K.M., Lothrop, C.D.: Genetic test for pyruvate kinase deficiency of basenjis Journal of the American Veterinary Medical Association 207:918-921, 1995. Pubmed reference: 7559024.

Whitney, K.M., Goodman, S.A., Bailey, E.M., Lothrop, C.D.: The molecular basis of canine pyruvate kinase deficiency Experimental Hematology 22:866-874, 1994. Pubmed reference: 7520391.