Submitted June 12, 2008
Accepted September 17, 2008
Mutation of the 
1-tubulin gene associated with congenital macrothrombocytopenia affecting microtubule assembly
Shinji Kunishima*, Ryoji Kobayashi, Tomohiko J Itoh, Motohiro Hamaguchi, and Hidehiko Saito
Department of Hemostasis and Thrombosis, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Japan
Department of Pediatrics, Hokkaido University Graduate School of Medicine, Sapporo, Japan
Division of Biological Sciences, Graduate School of Science, Nagoya University, Nagoya, Japan
Nagoya Central Hospital, Nagoya, Japan
* Corresponding author; email: kunishis{at}nnh.hosp.go.jp.
Congenital macrothrombocytopenia is a genetically heterogeneous group of rare disorders. We identified the first TUBB1 mutation, R318W, in a patient with congenital macrothrombocytopenia. The patient was heterozygous for Q43P, but this SNP did not relate to macrothrombocytopenia. Although no abnormal platelet 
1-tubulin localization/marginal band organization was observed, the level of 1-tubulin was decreased by ~50% compared to healthy controls. Large and irregular bleb protrusions observed in megakaryocytes derived from the patient's peripheral blood CD34+ cells suggested impaired megakaryocyte fragmentation and release of large platelets. In vitro transfection experiments in CHO cells demonstrated no incorporation of mutant 1-tubulin into microtubules but the formation of punctuated insoluble aggregates. These results suggested that mutant protein is prone to aggregation but is unstable within megakaryocytes/platelets. Alternatively, mutant 1-tubulin may not be transported from the megakaryocytes into platelets. W318 1-tubulin may interfere with normal platelet production, resulting in macrothrombocytopenia.
