Canine Macrothrombocytopenia is a condition characterized by oversized platelets and a low platelet count. The name is derived from words macro (large) and thrombocyte (platelets). This blood disorder is affecting Cavalier King Charles Spaniel, Norfolk Terriers and Cairn Terriers. The causative mutation was originally identified in the Cavalier King Charles Spaniel, and later a similar mutation was also discovered in affected Norfolk Terriers and Cairn Terriers.
Platelets, or thrombocytes, have a key role in bleeding prevention through clumping of blood vessel injuries. At a site of vascular injury, platelets are exposed to surface which is not from blood vessel, and they initiate to aggregate to each other, which results in formation of a hemostatic plug that will seal the defect. In the formation of this plug, fibrin has a role as its stabilizer.
Microtubules are a component of the cytoskeleton, and are very important in a number of cellular processes. One of such roles of microtubules is maintaining the disk shaped form of circulating platelets, and they also drive the orderly fragmentation of platelets from the megakaryocyte cytoplasm. Microtubules are heterodimers composed of alpha and beta monomers. Beta1- tubulin is a component of microtubules and is essential for the maintenance of platelet shape.
Canine Macrothrombocytopenia is characterized by abnormalities in size and count of platelets. Platelets in affected dogs function normally, and affected dogs do not show any health problems or prolonged bleeding time.
Macrothrombocytopenia in Norfolk Terriers and Cairn Terriers is associated with mutation in the beta1- tubulin gene, causing expression of malfunctional beta1- tubulin. This causes altered thrombopoietic mechanism and incorrect proplatelet formation in affected dogs.
Macrothrombocytopenia in Norfolk Terriers and Cairn Terriers is inherited in an autosomal recessive manner. Healthy parents of an affected puppy are obligate heterozygotes, and therefore carry one mutant allele. Heterozygotes have no symptoms. Dogs homozygous for the mutation will display the clinical signs of the disorder. At conception, 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.
Prevalence of carrier and affected dogs rate is very high. Although the condition is not life threatening, it is important to be aware whether your dog is affected. Affected dogs often receive inappropriate treatment with antibiotics, corticosteroids, or other medication because of confusion or lack of awareness of this disorder.