Thrombocytopenia in dogs

Thrombocytopenia is a disease of impaired blood clotting, manifested by severe bleeding conditions. Thrombocytopenia is caused by a reduced platelet count. In Cavalier King Charles Spaniels, a mutation in the gene for β1-tubulin (TUBB1) is responsible for the disease. It is a missense mutation c.745G>A that leads to defective fragmentation of megakaryocytes, the precursors of platelets. The thrombocytes produced are then larger (a condition referred to as macrothrombocytopenia) but their number is reduced. The same mutation was then demonstrated in chihuahuas, Russell terriers, King Charles spaniels, Labrador retrievers, Maltese dogs, poodles, and Shih-tzu.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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References:

Davis, B., Toivio-Kinnucan, M., Schuller, S., Boudreaux, MK. : Mutation in beta1-tubulin correlates with macrothrombocytopenia in Cavalier King Charles Spaniels. J Vet Intern Med 22:540-5, 2008. Pubmed reference: 18466252.