Klin Onkol 2006; 19(Suppl2): 411-414.
Summary
Background: Chromosomal translocations involving immunoglobulin loci (14q32/IGH, 2p11/IGK and 22q11/IGL) play an important role in pathogenesis of B cell leukemia and lymphoma. These aberrations lead to deregulated transcription of targeted oncogenes by their juxtaposition with the IGH transcriptional enhancer(s). Fluorescent in situ hybridization (FISH) showed to be a potential tool for identification of cancer-related genes located in breakpoint regions of chromosomal translocations. However, the commonly used „probe-mapping“ FISH strategy requires numerous experiments with consecutively selected probes from the narrowed down region and uses a significant amount of cytogenetic material. One of the alternative approaches, array comparative genomic hybridisation (aCGH), is a rapid technique that operates on DNA level and uses only a small amount of tumor material. In contrast to FISH, however, it analyzes only unbalanced aberrations. The aim of this study was to evaluate array comparative genomic hybridisation (aCGH) as a potential tool for a rapid mapping of breakpoint of nonreciprocal IGH-associated translocation in B cell leukemia and lymphoma.
Material and methods. For this study, we selected one case of B cell croniclymphocytic leukemia (CLL) with a complex karyotype including unbalanced der(14)t(1;14)(q25;q32) involving IGH. Genomic profiling of this case was performed using 1 megabase (Mb) aCGH. Validation of aCGH results was done by metaphase FISH with Bacterial Artificial Chromosome (BAC) clones and chromosome painting probes.
Results and conclusions. In one single aCGH experiment eight regions of genomic imbalances (4 gains and 4 losses) were identified. As expected, these imbalances included also duplication of 1q due to the der(14)t(1;14). Two consecutive BAC clones flanking the proximal breakpoint at 1q21.3 have been identified. These clones were further applied for metaphase FISH analysis that confirmed aCGH findings. Despite of 1 Mb resolution of the applied platform, these particular clones are separated by approximately 3 Mb. Given that this region is gene-rich, further BAC-mapping is required to identify the candidate gene located in the breakpoint region. Moreover, aCGH data helped us to correct original cytogenetic findings and precisely define karyotypic changes in this case. Our data provide additional evidence that aCGH is a powerful technique for molecular karyotyping of tumors and allows a rapid mapping of genomic imbalances, including breakpoints of non-reciprocal translocations. As shown in this study, the latter can be detected with high accuracy and sensitivity during a single experiment.
