The E2A product consists of a 189kb probe, labelled in red, located centromeric to the E2A (TCF3) gene, including the RH98588 marker, and a green probe covering a 163kb region located telomeric to the E2A gene, including the D19S883 marker.
The TCF3 (transcription factor 3) gene is located at 19p13.3. 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 (PBX homeobox 1) at 1q23.3 and HLF (HLF transcription factor, PAR bZIP family member) 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.
The t(1;19)(q23;p13) is the most common TCF3 rearrangement, being present in around 6% of childhood B-ALL1,2. According to the World Health Organization (WHO) classification of myeloid neoplasms and acute leukaemia, B lymphoblastic leukaemia/lymphoma with t(1;19)(q23;p13); TCF3-PBX1 is recognised as a distinct disease entity2. The functional fusion gene resides at chromosome 19. An unbalanced form of this translocation has been reported, with loss of der(1)1,2. Detection of the E2A-PBX1 fusion by molecular methods, such as FISH, is important, as a subset of B-ALLs has a karyotypically identical t(1;19) that involves neither TCF3 nor PBX1. E2A-PBX1 positive leukaemia was historically associated with a poor outcome, though modern intensive therapies have overcome this1,2,4.
The t(17;19)(q22;p13.) is a rare translocation that is present in around 1% of precursor B-ALL cases1. TCF3-HLF positive leukaemia is associated with adverse prognosis3,4.
Running our PETS protocol was taking upwards of 5 hours to complete based on the previous SOP. After the technical training visit from CytoCell, we were able to make some tweaks to reduce the protocol time down to just 1 hour and 15 minutes, with the same or better results.
Assistant Genetic Technologist, Leicestershire Genetics Centre, UK