The application of comparative genomic hybridization as an additional tool in the chromosome analysis of acute myeloid leukemia and myelodysplastic syndromes

In acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) there are frequently complex karyotypes with multiple structurally altered chromosomes, many of which are marker chromosomes of unknown origin. The aim of this study was to apply comparative genomic hybridization (CGH) to cases of AML or MDS in transformation submitted for routine cytogenetic analysis to investigate whether this approach would yield any further information and, if possible, to predict which cases would benefit from CGH analysis. Nineteen cases with AML or MDS in transformation were analyzed. CGH revealed nine cases with gains or losses of chromosomal material. In six of these cases the chromosomal location of this material was not apparent from cytogenetic analysis especially when multiple markers were present. By using fluorescence in situ hybridization (FISH) with specific libraries for the chromosome regions that showed discordance between CGH and conventional cytogenetics, we were able to identify the chromosome location of material within the karyotype. In this group of six patients, four cases of an unbalanced translocation involving regions of chromosomes 5 and 17 were characterized. Three of these cases had additional abnormalities, including two cases with regions of amplification in which oncogenes are located (MYC, MLL) and one case with a dic(7;21)(p10;p10). In all six cases it was possible to characterize complex chromosomal aberrations such as derivative chromosomes, marker chromosomes, and ring chromosomes. This study demonstrates that CGH can detect true gain and loss of critical chromosome regions more accurately than conventional karyotyping in cases with very complex karyotypes, and can thus prove useful in predicting prognosis and pinpointing areas of the genome that require further study. Also, CGH can be a useful technique to identify the origin of marker chromosomes, and it can assist in choice of probes for confirmatory FISH, when there is no clue provided from the analysis of G-banded chromosomes.