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Canine Macrothrombocytopenia
| Acronym: | MTC-R |
| Gene: | TUBB1 |
| Mutation: | c.5G>A |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Canine Macrothrombocytopenia is a condition characterized by oversized platelets and a low platelet count. The name is derived from the 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 the clumping of blood vessel injuries. At a site of vascular injury, platelets are exposed to the surface which is not from a blood vessel, and they initiate to aggregate with each other, which results in the 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 the 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 a mutation in the beta1- tubulin gene, causing the expression of malfunctioning beta1- tubulin. This causes altered thrombopoietin 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. The prevalence of carrier and affected dogs rate is very high. Although the condition is not life-threatening, it is important to be aware of 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.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Gelain ME, Tutino GF, Pogliani E, Bertazzolo W. Macrothrombocytopenia in a group of related Norfolk terriers. Vet Rec 167:493-4, 2010.
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.