Congenital Macrothrombocytopenia (Cairn and Norfolk Terrier Type)

Other Names: Macrothrombocytopenia, Macrothrombocytosis, Thrombocytopenia, MTC
Affected Genes: TUBB1
Inheritance: Autosomal Recessive
Mutation: chr24:44509479 (canFam4): G/A
Breed(s): Cairn Terrier, Lucas Terrier, Norfolk Terrier

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Common Symptoms

Congenital Macrothrombocytopenia (Cairn and Norfolk Terrier Type) is an inherited blood condition affecting dogs. This condition is diagnosed via microscopic examination of a blood smear. It is characterized by reduced numbers of normal sized Platelets in the blood (thrombocytopenia) and the presence of large platelets (macrothrombocytes). Affected dogs rarely exhibit clinical signs related to platelet abnormalities however, recognizing a congenital cause for macrothrombocytopenia is important because both the lack of platelets and large platelets can be associated with other clinically important diseases. In addition, some blood analyzer machines can misinterpret macrothrombocytes as red blood cells, thus further complicating diagnoses. Dogs affected with this condition do not show increased incidence of Hemorrhage and blood clotting times are normal.

Testing Tips

Genetic testing of the TUBB1 gene will reliably determine whether a dog is a genetic Carrier of Congenital Macrothrombocytopenia (Cairn and Norfolk Terrier Type). This disease is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the TUBB1 gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Dogs that are not carriers of the mutation have no increased risk of having affected pups.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


  • Boudreaux MK. Inherited platelet disorders. J Vet Emerg Crit Care (San Antonio). 2012 Feb;22(1):30-41. [PubMed: 22316339]
  • Gelain ME, Bertazzolo W, Tutino G, Pogliani E, Cian F, Boudreaux MK. A novel point mutation in the β1-tubulin gene in asymptomatic macrothrombocytopenic Norfolk and Cairn Terriers. Vet Clin Pathol. 2014 Sep;43(3):317-21. [PubMed: 25060661]
  • Gelain ME, Tutino GF, Pogliani E, Bertazzolo W. Macrothrombocytopenia in a group of related Norfolk terriers. Vet Rec. 2010 Sep 25;167(13):493-4. [PubMed: 20871084]