MOLECULAR VARIANTS OF THE 1-19-CHROMOSOMAL TRANSLOCATION IN PEDIATRICACUTE LYMPHOBLASTIC-LEUKEMIA (ALL)

The t(1;19)(q23;p13), a non-random chromosome rearrangement associated with childhood pre-B acute lymphoblastic leukemia (ALL), results at m olecular level in the hybrid E2A-PBX1 gene. This gene is expressed in a typical set of fusion transcripts and oncogenic chimeric proteins. H owever, the occurrence of t(1;19) molecular variants has been recently suggested. In an attempt to identify these variants, we analyzed 25 p ediatric cases of pre-B clg+ cell ALL. We used Southern blot analysis to detect E2A gene rearrangements and RT-PCR to detect chimeric E2A-pb x1 transcripts. In addition to seven cases with the molecular pattern usually associated with the t(1;19), we identified three molecular var iants. In one case, a variant E2A-pbx1 transcript showed 27 additional base pairs inserted in frame at the junction site. In two cases, Sout hern blot evidenced the expected E2A gene rearrangements. However, ext ensive RT-PCR analysis failed to detect any E2A-pbx1 transcript. These findings led us to hypothesize that a gene other than PBX1 might be i nvolved in these 1;19 variant translocations.