A 10-year-old boy was admitted to the hospital because of anemia detected after a two week history of fatigue, dizziness, nausea, headaches, and weight loss. A bone marrow investigation confirmed a diagnosis of acute lymphoblastic leukemia of the B-cell precursor phenotype. Chromosome G-banding analysis yielded the karyotype 46,XY,t(17;19)(q22;p13), and fluorescence in situ hybridization (FISH) analysis showed rearrangement of the genes TCF3 (on 19p13; accession number NM_03200 version 3) and HLF (on 17q22; accession number NM_002126 version 4) with the generation of a TCF3-HLF chimera. Polymerase chain reaction and sequencing analyses demonstrated the presence of two in-frame chimeric TCF3-HLF transcripts. In the first one, which corresponds to a type 2 fusion, exon 15 of TCF3 is fused to exon 4 of HLF. In the second, described here for the first time and named type 3, exon 14 of TCF3 is fused to exon 4 of HLF. Whether the type 3 chimeric transcript has the same DNA binding and transcriptional regulatory effect as type 1 and type 2 TCF3-HLF chimeras remains to be seen.
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