t(5;14)(q35;q32.2)

Cytogenetics Morphological	t(5;14), like other cryptic chromosomal aberrations, was discovered relatively recently and most subsequent studies have focused on molecular and clinical aspects of this entity to the exclusion of cytogenetics. This gap is aggravated by the uniquely large breakpoint cluster region (bcr) of the 14q32 partner gene, BCL11B (alias CTIP2, RIT1). Hence, detailed documentation of this interesting rearrangement is largely based on data obtained using t(5;14) T-ALL cell lines which hitherto all carry submicroscopic insertions, both ins(5;14) and ins(14;5), instead of conventional reciprocal translocations. If verified in patient material, detailed analysis of such configurations may reveal neighboring genes or regulators inimical to the oncogenic activity of t(5;14), and therefore excluded by the more selective insertional rearrangements.
	G-banding of t(5;14)(q35;q32.2) in a pediatric T-ALL leukemia cell line (CCRF-CEM) illustrating the cryptic nature of this rearrangement. Hence normal and rearranged homologs are indistinguishable by G-banding, as are standard and rare variant t(5;14) subtypes. In chromosome painting images only a minority of cells in even superior preparations show the t(5;14).
Cytogenetics Molecular	The proximities of the 14q32.2, and of both standard and variant 5q35 breakpoints to their respective telomeres, impairs FISH detection using chromosome painting probes except in optimal preparations. The tendency of t(5;14) to involve microinsertions (in both directions), together with the sheer magnitude of the BCL11B bcr, impedes detection by specific BAC/PAC combinations.
	Upper image depicts results of chromosome painting in an above average T-ALL cell (CCRF-CEM) with t(5;14) and concurrent ins(14;5). Note absence of visible signs betraying reciprocal exchange. Chromosome painting was performed using Cambio probes (Cambridge, UK) for chromosomes 5 (TexasRed), and 14 (Cy3). Middle image depicts standard t(5;14)(q35.1;q32.2) as represented by ins(5;14)(q35.1;q32.2q32.2) in cell line DND-41 which activates TLX3 transcription by juxtaposition with part of the noncoding region of BCL11B (clones shown below). Insert shows fiber-FISH confirming the regions juxtaposed. Lower image summarizes breakpoint data for t(5;14)(q35;q32) in T-ALL at three loci: TLX3 (standard translocation), NKX2-5 (variant translocation), and BCL11B (both translocations). Patient and cell line breakpoints are shown red and blue, respectively, together with insertion data from cell line DND-41. The NKX2-5 patient breakpoint included for comparison is from a t(5;14)(q35.2;q11.2) patient where TRAD is the activating partner. Coordinates are given in Mbp. Note the circa 1 Mbp 14q32.2 bcr which effectively covers the 3'-BCL11B regulatory region, while TLX3 breakpoints cover a "modest" 90 Kbp. NKX2-5 cases are too rare to allow bcr delineation.
Variants	A microscopically synonymous variant, t(5;14)(q35.2;q32.2), whereby the closely related and neighboring NKX2-5 is juxtaposed to BCL11B, has proved frustratingly difficult to identify clinically despite occurring in two widely used T-ALL cell lines, CCRF-CEM and PEER. NKX2-5 is ectopically activated in t(5;14)(q35.2;q11.2) where it is juxtaposed with TRAD. The diagnostic caveats for the standard translocation also apply: detection of variant t(5;14) by RT-PCR is likely to pose fewer technical difficulties than cytogenetic detection by FISH.

	Figure 1 shows RT-PCR analysis of genes involved in t(5;14)(q35;q32) in T-ALL cell lines PEER and CCRF-CEM, both expressing NKX2-5 instead of TLX3. Figure 2 shows expression array data converted into a heat-map and demonstrate gene activities in five T-ALL cell lines: ALL-SIL (TRAD/TLX1), CCRF-CEM (NKX2-5/BCL11B), HPB-ALL (TLX3/BCL11B), PEER (NKX2-5/BCL11B), JURKAT (negative control). Red indicates high, green low, and black medium expression level. Note expression of homeobox genes is restricted to presence of corresponding translocation.

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