Mutation of the beta1-tubulin gene associated with congenital macrothrombocytopenia affecting microtubule assembly.
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 single-nucleotide polymorphism (SNP) did not relate to macrothrombocytopenia. Although no abnormal platelet beta1-tubulin localization/marginal band organization was observed, the level of beta1-tubulin was decreased by approximately 50% compared with 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 Chinese hamster ovary (CHO) cells demonstrated no incorporation of mutant beta1-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 beta1-tubulin may not be transported from the megakaryocytes into platelets. W318 beta1-tubulin may interfere with normal platelet production, resulting in macrothrombocytopenia.
Department of Hemostasis and Thrombosis, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Japan. kunishis@nnh.hosp.go.jp
Shinji
S
Kunishima
Ryoji
R
Kobayashi
Tomohiko J
TJ
Itoh
Motohiro
M
Hamaguchi
Hidehiko
H
Saito
D019943:Amino Acid Substitution; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D016466:CHO Cells; D002648:Child; D006224:Cricetinae; D003412:Cricetulus; D030342:Genetic Diseases, Inborn / Q000235:genetics* / Q000378:metabolism*; D006579:Heterozygote; D006801:Humans; D008297:Male; D008533:Megakaryocytes / Q000378:metabolism; D008870:Microtubules / Q000235:genetics* / Q000378:metabolism*; D020125:Mutation, Missense; D020641:Polymorphism, Single Nucleotide; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000235:genetics* / Q000378:metabolism*; D014404:Tubulin / Q000235:genetics* / Q000378:metabolism*
D014404:Tubulin