title: Characterization of a patient with atypical amegakaryocytic thrombocytopenia.
abstract: We report a 6-year-old girl with amegakaryocytic thrombocytopenia, the first case of this rare congenital disorder not to have an MPL gene mutation. Although no mutations were identified in MPL, Mpl protein was absent in the platelets and TPO induced phosphorylation of the Janus tyrosine kinase 2 (Jak2) was not detected. In addition to the defect of Mpl, the patient demonstrated markedly reduced expression of glycoprotein VI (GPVI) in contrast to normal expression of other platelet-specific proteins GPIb alpha, GPIb beta, and GPIIb. To explore the causes for the absence of Mpl, the entire coding region of Jak2 and AML1 were sequenced and no mutations were identified. To our knowledge, this is the first report that describes a case of amegakaryocytic thrombocytopenia that is not caused by a mutation in MPL and demonstrates the severe impairment of GPVI expression on platelets.
authors.affiliation: Division of Medical Biochemistry, Department of Biomolecular Sciences, Saga Medical School, Saga, Japan. kanajit@med.kurume-u.ac.jp
authors.forename: Sachiko
authors.initials: S
authors.lastname: Kanaji
authors.forename: Taisuke
authors.initials: T
authors.lastname: Kanaji
authors.forename: Masahiro
authors.initials: M
authors.lastname: Migita
authors.forename: Shinji
authors.initials: S
authors.lastname: Kunishima
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Kunicki
authors.forename: Takashi
authors.initials: T
authors.lastname: Okamura
authors.forename: Kenji
authors.initials: K
authors.lastname: Izuhara
mesh_terms: D020413:3' Untranslated Regions / Q000235:genetics; D001792:Blood Platelets / Q000378:metabolism; D002648:Child; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D008533:Megakaryocytes / Q000378:metabolism*; D016366:Open Reading Frames / Q000235:genetics; D010375:Pedigree; D015398:Signal Transduction; D013921:Thrombocytopenia / Q000235:genetics / Q000378:metabolism*
chemical_list: D020413:3' Untranslated Regions; D018076:DNA, Complementary