Analysis of acute leukemias with MLL/ENL fusion transcripts: identification of two novel breakpoints in ENL

t(11;19)(q23;p13.3); is one of the common chromosomal translocations in acute leukemias involving MLL rearrangements. This translocation generates MLL/ENL fusion transcripts. In a study of acute leukemias, 148 patients were identified to have MLL rearrangements by Southern blot analysis. Reverse transcriptase-polymerase chain reaction (RT-PCR) assay, using primer sets covering the 2 previously described breakpoints at exons 2 and 7 of ENL detected 11 samples harboring MLL/ENL. complementary DNA panhandle PCR further identified 4 additional cases with novel breakpoints in ENL at exon 4 or 6. Sequencing analysis showed that all novel fusion transcripts were in-frame. The conventional cytogenetic analysis failed to detect t(11;19) in 6 of 13 cases. Of 15 patients with MLL/ENL, 7 had precursor B-cell acute lymphoblastic leukemia, 4 had T-cell acute lymphoblastic leukemia, and 4 had acute myeloid leukemia. The present study showed that PCR-based techniques are more sensitive than conventional karyotyping for detecting MLL/ENL fusions and an extra antisense primer at exon 6 of ENL should be included in RT-PCR assay to ensure complete detection of all MLL/ENL fusion transcripts.