Acute basophilic leukemia (ABL) is a rare subtype of acute leukemia with clinical features and symptoms related to hyperhistaminemia because of excessive growth of basophils. No known recurrent cytogenetic abnormality is associated with this leukemia. Rare cases of t(X;6)(p11;q23) translocation have been described but these were sporadic. We report here 4 cases of ABL with a t(X;6)(p11;q23) translocation occurring in male infants. Because of its location on chromosome 6q23, MYB was a good candidate gene. Our molecular investigations, based on fluorescence in situ hybridization and rapid amplification of cDNA ends, revealed that the translocation generated a MYB-GATA1 fusion gene. Expression of
MYB-GATA1
IntroductionAcute myeloid leukemia (AML) accounts for 15%-20% of cases of childhood leukemia. 1-2 Acute basophilic leukemia (ABL) is a rare subtype of acute leukemia. Clinical features are close to those of poorly differentiated AML with, in some cases, symptoms related to hyperhistaminemia because of excessive expansion of the basophil compartment. 3 The diagnosis of ABL is associated with detection of basophil blast cells. To date, because of the rarity of ABL cases, no recurrent cytogenetic abnormality has been described. Rare cases of t(X;6)(p11;q23) translocations have been reported but these were sporadic. [4][5] Of note, a very recent paper reported the cloning of the t(X;6)(p11;q23) in a case of acute monoblastic leukemia. 6 We report here 4 cases of ABL with a t(X;6)(p11;q23) translocation occurring in male infants. Patients P1 and P2 have been reported previously. 4 Because of its location on chromosome 6q23 and its well established involvement in oncogenesis, 7 MYB was a good candidate gene. Our molecular investigations, based on fluorescence in situ hybridization (FISH) and rapid amplification of cDNA ends (RACE), revealed that the translocation generated a MYB-GATA1 fusion gene. This chimera commits myeloid cells to the granulocyte lineage and blocks their differentiation.
Methods PatientsCharacteristics of the patients fit with the diagnosis of ABL (supplemental Methods and supplemental Table 1, available on Blood Web site; see the Supplemental Materials link at the top of the online article).
FISHCytogenetic analysis of bone marrow samples was performed by standard methods and FISH as described 8 (supplemental Methods, supplemental Figure 1).
Cloning of MYB-GATA1MYB-GATA1 was isolated using the 5Ј/3Ј RACE Kit (Roche). Full-length MYB-GATA1 cDNA was cloned into the retroviral pMSCVIresEGFP vector (pMIE-MG; supplemental Table 2).
Screening of mutationsThe mutational status of FLT3, NPM1, WT1, CEBPa, K-RAS, N-RAS, IDH1, IDH2 was investigated by high-resolution melting and multiplex PCR (supplemental Table 2).
CFC assaysColony forming cell (CFC) assays were performed on mouse lineagenegative (lin Ϫ ) cells harvested from C57BL/6 mice, sorted using a Lineage Cell Depletion Kit (Miltenyi Biotec) and transduced with pMIE (control) or pMIE-MG (MYB-GATA1) retroviral vectors. Cells were seeded in triplicate...