E2A Breakapart Probe

Translocations involving the E2A (Transcription Factor 3) gene have been generally accepted as non-random chromosome translocations in childhood B-ALL. At present, there are two partner genes, PBX1 and HLF on chromosomes 1 and 17 respectively, which become fused to E2A as a result of the t(1;19) and t(17;19) translocations forming the E2A/PBX1 and E2A/HLF fusion proteins. The former is more common, being present in about 5% of paediatric ALLs1 whilst the other is present in some 1%. Both are associated with poor outcome, with the t(1;19) patients being at high risk of relapse. Both fusion proteins have transcriptionally active domains but their true pathway to the leukaemia is yet to be completely understood.

Detection of the t(1;19) is best carried out using molecular methods such as FISH as the fusion has been shown to be missed in 20 to 25% of patients by standard cytogenetics.2 The E2A probe mix consists of a 3' probe, labelled in green, covering 164kb 3' of the gene spanning the markers D19S883 and D2S2123 whilst the 5' region probe, labelled in red, (191kb) is 157kb from the 5' end of the gene.