Identification of parental chromosomes involved in translocations BCR-ABL, t(9;22) and PML-RARA, t(15;17)

Cells of blood and bone marrow often exhibit a genome- or ploidywise organization of the two haploid sets, representing apparently maternal and paternal chromosomes in interphase nuclei and in metaphase spreads. This provides the opportunity to perform "genomic karyotyping." Such application of karyotyping may indicate whether two chromosomes involved in a translocation are both maternal, both paternal, or intermingled, i.e., one maternal and the other paternal (we refer to this as mixed). The parental origin for these translocations likely has profound differences and implications in disease expression and response to treatments, making such information very important to personalized medicine. In this mini-review, we present our observations from specimens with translocations BCR-ABL, t(9;22) and PML-RARA, t(15;17). About 20% metaphases of these specimens indicated ploidywise organization and were amenable to genomic karyotyping analysis. Fluorescence in situ hybridization (FISH) probes for BCR-ABL translocation suggest a close approximation of the HSA 9 and 22, as control values for false-positive signals run from approximately 5-10%. Given a ploidywise distribution of the maternal and paternal sets of chromosomes, it would be expected that the chromosomes involved in the translocation t(9;22) would more often belong to one of the two genomes, either maternal or paternal. Contrastingly, HSA 15 and 17 are not considered as spatially close to each other and therefore an intragenomic involvement would be rarer for translocation t(15;17). In 14 out of the 21 (66.6%) specimens with informative metaphases, the chromosomes involved in the translocation BCR-ABL were restricted to one of the two genomes--either maternal or paternal. In cases of translocation PML-RARA only 4 out of 21 (19.1%) specimens indicated an intragenomic involvement. These simple yet informative analyses of cancer-related translocations show profound underlying genomic origins and lend support to genomic karyotyping.