Macrothrombocytopenia (Discovered in Norfolk and Cairn Terrier)

Macrothrombocytopenia is a blood disorder characterized by oversized blood platelets, which play an important role in blood clotting when a blood vessel is injured.

Found in

1 in 1,000 dogs

in our testing

Key Signs

Low platelet count, Macroplatelets

Age of Onset

At birth

Present at birth


Autosomal Recessive

For autosomal recessive disorders, dogs with two copies of the variant are at risk of developing the condition. Dogs with one copy of the variant are considered carriers and are usually not at risk of developing the disorder. However, carriers of some complex variants grouped in this category may be associated with a low risk of developing the disorder. Individuals with one or two copies may pass the disorder-associated variant to their puppies if bred.

Likelihood of the Condition

Moderate-high likelihood

At risk dogs are likely to show signs of this disease in their lifetime.

What to Do

Here’s how to care for a dog with Macrothrombocytopenia

Partner with your veterinarian to make a plan regarding your dog’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about Macrothrombocytopenia

Congenital macrothrombocytopenia is characterized by oversized platelets, also called macroplatelets, and an abnormally low number of platelets. Macroplatelets function normally and the affected dogs do not exhibit any health problems due to either the size or the lower platelet count. Macrothrombocytopenia is not associated with spontaneous bleeding.

While this disorder is relatively mild, it is important not to mistake macrothrombocytopenia for other more severe conditions characterized by low platelet counts.

For Breeders

Planning to breed a dog with this genetic variant?

There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.

This condition is autosomal recessive meaning that two copies of the mutation are needed for signs to occur. However signs of this condition are very mild, and are unlikely to affect a dog's wellbeing. Breeding a carrier dog with a clear dog will not produce any puppies with clnical signs of this condition. About half of the puppies will have one copy (carriers) and half will have no copies of the Macrothrombocytopenia mutation. Breeding a dog with two copies of the Macrothrombocytopenia mutation with a clear dog will produce a litter containing all carriers. Please note: It is possible that signs similar to the ones caused by the Macrothrombocytopenia mutation could develop due to a different genetic or clinical cause.

Technical Details

Gene TUBB1
Variant G>A
Chromosome 24
Coordinate 43,761,303

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Gelain, M. E., Tutino, G. F., Pogliani, E., & Bertazzolo, W. (2010). Macrothrombocytopenia in a group of related Norfolk terriers. Veterinary Record. View the article