Pyruvate kinase (PK) deficiency
Pyruvate kinase is a key enzyme in energy metabolism in red blood cells. This inherited disorder causes a deficiency in this enzyme which results in a marked shortening of the life span of red blood cells, and therefore a severe hemolytic anemia - low red blood cell numbers due to cell breakdown.
This is an autosomal recessive trait which means both parents of an affected dog are carriers of the disorder. Carriers have about one half normal enzyme activity in red blood cells, and are clinically unaffected.
Dogs with PK deficiency usually show signs by 4 months to 1 year of age. Because of the severe anemia (low levels of red blood cells), affected dogs are slow to grow, and show a mild weakness and a low tolerance for exercise. Unfortunately these dogs also gradually develop changes in their bones, specifically replacement of the bone marrow with fibrous tissue, and hardening or abnormal density of bone (called myelofibrosis and osteosclerosis). Dogs with pyruvate kinase deficiency usually die before 4 years of age, due to bone marrow failure and/or liver disease.
Signs of anemia include pale mucous membranes (your dog's gums for example), an increased heart rate and a reduced tolerance for exercise. Your veterinarian will do blood tests to determine the cause of the anemia which in this disorder is due to increased red blood cell breakdown. Further tests will be required to diagnose this specific condition as the cause of the hemolytic anemia.
There is no specific treatment for this disorder, other than supportive care as necessary.
HEMATOLOGY: persistent, severe (PCV 12 to 26%), highly regenerative anemia which becomes less responsive as the dog ages.
DIAGNOSIS: Erythrocytes from affected dogs completely lack the normal R-type PK isoenzyme, but they do have an abnormal M-type PK isoenzyme. Thus special laboratory tests are required to diagnose a PK deficient dog, rather than simply measuring total PK activity. Carrier dogs, with half normal activity, can also be identified. Check with your clinical pathology lab for requirements for sample submission. A DNA diagnostic test has been developed for Basenjis and West Highland white terriers which can identify carriers and affected animals at any age (see reference below).
OTHER SIGNS: hepatosplenomegaly, progressive myelofibrosis and osteosclerosis, +/- terminal liver disease with hemochromatosis and cirrhosis.
Because this is an autosomal recessive trait, both parents of affected dogs carry the defective gene. Neither affected (homozygous) or carrier dogs (heterozygous) should be used for breeding. There is a DNA test that can identify carrier dogs at any age (see reference below). Many affected and carrier dogs have already been removed from the breeding population.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Harvey, J.W. 1995. Congenital hemolytic anemias and methemoglobinemias. ACVIM-Proceedings of the 13th Annual Veterinary Medical Forum: 37-40.
Henderson A. Anemia, Hemolytic. In: Côté E, ed. Clinical Veterinary Advisor Dogs and Cats. Missouri: Mosby Elsevier, 2007:64-66.
Sargan DR. Pyruvate kinase deficiency. In IDID - Inherited diseases in dogs:web-based information for canine inherited disease genetics.
vetGen - information on genetic testing available (Basenjis and West Highland white terriers)