E2A, 19p13.3, Green
PBX1, 1q23.3, Red
The E2A probe, labelled in green, contains two probes (110kb and 146kb) that cover the 3’ end of the E2A (TCF3) gene and flanking region and a 321kb probe that covers a region 5’ (centromeric) to the gene. The PBX1 probe, labelled in red, contains two probes (147kb and 110kb) that map within the PBX1 gene and a 117kb probe that maps 3’ (telomeric) to the gene.
Probe information
The TCF3 (transcription factor 3) gene is located at 19p13.3 and PBX1 (PBX homeobox 1) at 1q23.3. Translocations involving TCF3 are some of the most common rearrangements in childhood B-cell acute lymphoblastic leukaemia (ALL)1,2.
Two of the main TCF3 partners are PBX1 at 1q23.3 and HLF at 17q22. These become fused to TCF3 as a result of the t(1;19)(q23;p13) and t(17;19)(q22;p13) translocations, forming the TCF3-PBX1 and TCF3-HLF fusion genes, respectively. A rare cryptic inversion, inv(19)(p13;q13), has been reported to fuse TCF3 to TFPT (TCF3 fusion partner), resulting in the TCF3-TFPT fusion gene1.
UK and European best practice guidelines suggest that when a TCF3 rearrangement is identified in B-cell ALL, it is important to distinguish between t(17;19)(q22;p13) and t(1;19)(q23;p13) as the former translocation is associated with adverse prognosis3,4.
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