Macrothrombocytopenia (MTC) – Cavalier King Charles Spaniel

Thrombocytopenia or macrothrombocytopenia (MTC) is a hereditary disorder characterized by a reduced number of blood platelets (thrombocytes), many of which are enlarged. Thrombocytes play an essential role in blood clotting (coagulation). Mutations in the ß1‑tubulin (TUBB1) gene have been identified as the cause of this reduction. Depending on the specific variant, symptoms may range from prolonged bleeding times to an apparently healthy animal.
The variant in this test occurs in the Cavalier King Charles Spaniel and is caused by a recessive mutation in TUBB1. This form is generally considered mild: affected dogs often show low platelet counts and enlarged platelets, but many remain clinically healthy without spontaneous bleeding problems.
A related mutation has been identified in the Norfolk Terrier and Cairn Terrier. This version is regarded as more severe, with affected dogs more likely to show clinical signs such as prolonged bleeding times, petechiae, or bruising.