Mutation in β1-tubulin correlates with macrothrombocytopenia in cavalier king charles spaniels

Background: Cavalier King Charles Spaniels (CKCS) have a high prevalence of inherited macrothrombocytopenia. The purpose of this study was to determine if a mutation in beta 1-tubulin correlated with presumptive inherited macrothrombocytopenia. Hypothesis: A mutation in beta 1-tubulin results in synthesis of an altered beta 1-tubulin monomer. alpha-beta tubulin dimers within microtubule protofilaments are unstable, resulting in altered megakaryocyte proplatelet formation. Animals: Blood samples were obtained from CKCS and non-CKCS dogs. Methods: DNA was used in polymerase chain reaction (PCR) assays to evaluate beta 1-tubulin. Platelet numbers and mean platelet volume (MPV) were evaluated for a correlation with the presence or absence of a mutation identified in beta 1-tubulin. Platelets obtained from homozygous, heterozygous, and clear CKCS were further evaluated using electron microscopy and immunofluorescence. Results: A mutation in the gene encoding beta 1-tubulin correlated with macrothrombocytopenia in CKCS. Electron microscopy and immunofluorescence studies suggest that platelet microtubules are present but most likely are unstable and decreased in number. Conclusions and Clinical Importance: The macrothrombocytopenia of CKCS correlated with a mutation in beta 1-tubulin. alpha-beta tubulin dimers within protofilaments most likely are unstable, leading to altered proplatelet formation by megakaryocytes. This information will aid in distinguishing inherited from acquired thrombocytopenia. It also provides insight into the mechanism of platelet production by megakaryocytes, and also may prove useful in understanding heart-related changes in macrothrombocytopenic CKCS with concurrent mitral valve regurgitation.