Canine Pyruvate Kinase Deficiency (PK Deficiency)
Canine Pyruvate Kinase Deficiency (PK Deficiency) is a genetic disorder characterized by low levels of pyruvate kinase enzyme in the red blood cells. The disorder was first documented in Basenjis, and it is the most common inherited erythroenzymopathy in dogs. PK deficiency has been reported in dogs, cats and human beings. Several breeds are more prone to the disorder, such as Basenji, Beagle, West Highland White Terrier, Cairn Terrier, Miniature Poodle, Dachshund, Chihuahua, Pug and American Eskimo dogs.
Reed blood cells, known as erythrocytes, have an important role within the body to deliver oxygen to the body tissues via blood circulation through cardiovascular system. Enzyme important for proper function of erythrocytes is the pyruvate kinase (PK), which acts as a regulatory enzyme in anaerobic glycolysis and energy generation. PK catalyzes last step of glycolysis, in which phosphoenolpyruvate is converted to pyruvate. A deficiency in pyruvate kinase results in red blood cells with decreased energy. In such red blood cells, ATP needed for energy cannot be synthesized, and cellular death occurs.
Characteristics and Symptoms
Symptoms of canine pyruvate kinase deficiency develop between 4 months to one year of age. Affected dogs suffer from severe hemolytic anemia. Typical PK deficiency symptoms are exercise intolerance, episodes of severe weakness, rapid heart rate, heart murmurs, pale gums, and stunted growth. The erythrocytic osmotic fragility curves appear in normal sigmoid shape. When measuring iron levels affected dogs show severe hyperferritinemia (high levels of ferritin in the blood) and high serum iron concentrations. Radiography examination shows increased cortical bone and increased blotchy bone density in the marrow areas. Ultrasound of abdominal area shows liver and spleen enlargement, condition known as hepatosplenomegaly. Osteosclerisus of the long bones may be present as well. Necropsy findings include diffuse icterus, dense cortical and trabecular bone, and scant bone marrow which sinks in water. Bone marrow analysis reveals erythroid hyperplasia, mild fibroplasia and hemosiderosis.
Affected dogs usually die between 1 to 4 years of age because of progressive anemia and hepatic failure. PK deficiency clinical signs show progressive nature and affected dogs usually need to be euthanized.
Canine Pyruvate Kinase Deficiency is associated to PK-LR gene mutation. The disorder is inherited as an autosomal recessive disorder. Healthy parents of an affected puppy are obligate heterozygotes, and therefore carry one mutant allele. Heterozygotes have no symptoms. At conception, when mating two carrier dogs, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
Gultekin GI, 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. 2012 Jul-Aug;26(4):935-44.