A NOVEL BCR-ABL, FUSION GENE (E6A2) IN A PATIENT WITH PHILADELPHIA CHROMOSOME-NEGATIVE CHRONIC MYELOGENOUS LEUKEMIA

A novel variant of the chimeric BCR-ABL mRNA transcript was detected i n a patient with Philadelphia chromosome-negative (Ph(-)) chronic myel ogenous leukemia (CML) by multiplex reverse transcription polymerase c hain reaction (RT-PCR). Sequence analysis of the fusion region of the amplified cDNA fragment showed an in-frame joining of exon e6 of the B CR gene and exon a2 of the ABL gene, giving rise to an e6a2 BCR-ABL tr anscript. This finding was confirmed by Southern blot analysis using a specific probe corresponding to intron 6 of the BCR gene, whereas con ventional Southern blot for rearrangement of the major breakpoint clus ter region (M-bcr] was negative, Western blot studies detected a BCR-A BL protein slightly larger than p185 BCR-ABL. Metaphase fluorescence i n situ hybridization showed an insertion of ABL material into the BCR region without reciprocal BCR translocation. The findings in this case show that atypical BCR-ABL transcripts are detectable even in Ph(-) C ML patients without M-bcr-rearrangements. Multiplex PCR using primers that allow for amplification of all known BCR-ABL transcripts is an ap propriate method to exclude these rare variants. (C) 1996 by The Ameri can Society of Hematology.