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Pyruvate kinase is an enzyme present in red blood cells (RBC). It helps to produce energy for the RBC by participating in the breakdown of glucose. With a pyruvate kinase deficiency, there is a reduced amount of energy for the cells, leading to a buildup of secondary breakdown products. These cells are affected and get flagged by the spleen as abnormal, ultimately getting destroyed. This whole process causes a premature death of red blood cells and leads to a decreased amount of circulating RBCs that are needed for oxygen transport to the body.
Pyruvate kinase deficiency is an inherited disorder of the PK-LR gene that has an autosomal recessive pattern. This means that both parents need to pass on one copy of the gene for affected individuals to show clinical signs. Individuals with only one gene are carriers, but are affected clinically. Interestingly, different mutations of the same PK-LR gene have been identified for different breeds of dogs and cats.
There are multiple breeds of dogs and cats that can have this genetic disorder, including:
- West Highland White Terriers
- Cairn Terriers
- Miniature Poodles
- Labrador Retrievers
- Domestic short hair
- Egyptian Maus
- Maine Coon Cats
- Norwegian Forest Cats
The most common presenting signs for dogs and cats with pyruvate kinase deficiency are lethargy, exercise intolerance, and anemia. The affected animals tend to be young when clinical signs are first noted, commonly under 2 years of age. Clinical signs closely mimic other types of hemolytic anemia, including auto-immune hemolytic anemia. Patients are often mistaken for having immune-mediated hemolytic anemia, but when they fail to respond to treatment, further genetic testing is evaluated.
Physical exam findings often include:
- Pale mucous membranes/pallor
- Icteric mucous membranes/jaundice
- Large spleen on abdominal palpation
- Elevated heart rate
- Elevated respiratory rate
Pets with pyruvate kinase deficiency have chronic anemia, therefore, they are able to compensate for their anemia and tend to tolerate it better than pets who acutely become anemic. Patients with hemolytic anemia that do not have this genetic mutation tend to be much sicker and more affected than pyruvate kinase deficiency patients.
There is no cure for pyruvate kinase deficiency, and treatment is purely supportive. Treatment during times of crisis involves blood transfusions to improve their anemia. Occasionally, treatment will include corticosteroids for their anti-inflammatory properties.
Dogs and cats with pyruvate kinase deficiency tend to do well for multiple years of their lives, but have a shortened life span compared to an non-affected individual of the same breed. Long-term consequences of this disease include bone marrow and liver failure. Some studies have noted that dogs with this genetic mutation have end stage bone marrow and liver failure by 5 years of age. One study showed that cats with this mutation passed away or were euthanized 1 – 7.5 years after diagnosis.
There are multiple laboratories that do genetic testing on potentially affected individuals or before breeding to confirm that they are not carriers. Because different breeds of animals have different mutations of the same genes, genetic testing should be done through labs that conduct specific breed-related panels. If conducting testing prior to breeding, all individuals that are carriers should be left out of breeding pools, as they can pass it on to offspring.