An internal tandem duplication (ITD) of the FLT3 gene is found in nearly 20% of acute myeloid leukemia (AML) and 5% of myelodysplastic syndrome cases. Our serial studies on 51 samples with the FLT3 gene mutation indicated that the ITD was frequently (47/51) clustered in the tyrosine-rich stretch from codon 589 to 599 and rarely (3/51) in its downstream region, both of which are located within the juxtamembrane (JM) domain. One remaining sample had an insertion into the JM domain of nucleotides of unknown origin. To eludicate the biological relevance of the ITD or the insertion, we expressed various types of mutant FLT3 in Cos 7 cells. All mutant FLT3 studied were ligand-independently dimerized and their tyrosine residues were phosphorylated. The Y589 of FLT3 was essential for the phosphorylation in the wild FLT3, but a Y589F conversion did not affect the phosphorylation status of the mutant FLT3. These findings suggest that the elongation of the JM domain rather than increase of tyrosine residues causes gainof-function of FLT3. Thus, ITD is a novel modality of somatic mutation which activates its product. Since the DNA corresponding to codon 593 to 602 potentially forms a palindromic intermediate, we propose that a DNA-replication error might be associated with generating the ITD of the FLT3 gene.

Background. Efavirenz (EFV) is metabolized primarily by cytochrome P450 2B6 (CYP2B6), and high plasma concentrations of the drug are associated with a GrT polymorphism at position 516 (516GrT) of CYP2B6 and frequent central nervous system (CNS)-related side effects. Here, we tested the feasibility of genotype-based dose reduction of EFV.Methods. CYP2B6 genotypes were determined in 456 human immunodeficiency virus type 1 (HIV-1)-infected patients who were receiving EFV treatment or were scheduled to receive EFV-containing treatment. EFV dose was reduced in CYP2B6 516GrT carriers who had high plasma EFV concentrations while receiving the standard dosage (600 mg). EFV-naive homozygous CYP2B6 516GrT carriers were treated with low-dose EFV. In both groups, the dose was further reduced when plasma EFV concentration remained high.

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 ␤1-tubulin localization/marginal band organization was observed, the level of ␤1-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 ␤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. IntroductionCongenital macrothrombocytopenia is a genetically heterogeneous group of rare disorders. [1][2][3] The most frequent forms include MYH9 disorders, such as May-Hegglin anomaly, and Bernard-Soulier syndrome. In approximately half of the cases the pathogenesis remains unknown; thus, a definite diagnosis is not possible. The linkage between the membrane skeleton and cytoskeletal actin filaments as well as the marginal microtubule band maintains normal platelet morphology. 4,5 Defects in these systems may result in macrothrombocytopenia. The microtubules are assembled from ␣-and ␤-tubulin heterodimers. ␤1-Tubulin expression is restricted in the megakaryocyte/platelet lineage. 6 Tubb1 knockout mice show thrombocytopenia and spherical platelets. 7 TUBB1 Q43P functional polymorphism has been reported. However, it may not be relevant to macrothrombocytopenia. 8 We identified the first TUBB1 mutation affecting microtubule assembly in congenital macrothrombocytopenia. Methods PatientThe patient was a 7-year-old boy who was incidentally found to have thrombocytopenia (platelets, 40-60 ϫ 10 9 /L). He was diagnosed with immune thrombocytopenic purpura. Peripheral blood smears showed the prominent appearance of giant platelets. Electron microscopy showed no other abnormalities ( Figure 1A,B). There were no leukocyte inclusion bodies, confirmed by myosin IIA localization. 9 The platelets aggregated normally with adenosine diphosphate (ADP), collagen, and ristocetin. Flow cytometry showed normal expression of platelet GPIb/IX. An initial bone marrow examination revealed normal megakaryocyte number and morphology. The mother of the patient also had macrothrombocytopenia. Peripheral blood samples were obtained after the mother gave informed consent in accordance with the Declaration of Helsinki for the study, which was approved by the...

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