High-Resolution Genomic Arrays Facilitate Detection of Novel Cryptic Chromosomal Lesions in MDS.

The evolution of abnormal hematopoietic clones characterized by acquired chromosomal abnormalities is the central event in the pathogenesis of MDS. Defective chromosomes have significant clinical implications in the management of MDS and suggest the presence of an inherent chromosomal instability. As karyotypic lesions are not found in all MDS patients, it is possible that in some the dysplastic clone may evolve without a chromosomal defect or, more likely, the resolution of routine metaphase cytogenetics is not sufficient to detect smaller lesions; in many instances lack of growth precludes the analysis.

Array-based comparative genomic hybridization (A-CGH) allows for a high-resolution genomic scan that circumvents some of the limitations associated with the use of conventional cytogenetics. We hypothesized that high-resolution genomic analysis of genetic gains and losses by A-CGH may detect cryptic lesions, particularly in patients with negative/non-informative cytogenetics that may be of clinical/scientific significance. We examined bone marrow cells from 39 MDS patients (18 RA/RARS, 11 RAEB-t, 6 CMML and 4 secondary AML) and 11 controls using a 2632 BAC microarray and CGH. Dye swapping on duplicate arrays assured reproducibility of the CGH results, confirmed globally by a high resolution 50K SNP microarray in 4 patients and by microsatellite analysis in others.

By traditional cytogenetics 19 patients had chromosomal lesions, 18 were normal and 2 tests non-informative. When A-CGH was applied, a normal karyotype was found in only 15% of patients in comparison to 46% by metaphase cytogenetics. Of note is that both cases with uninformative cytogenetics showed an abnormal CGH result and in several patients (N=11) with an abnormal karyotype additional lesions were found. Karyotypic results were confirmed in 7 cases; discordant analysis may be due to a lower proportion of dysplastic cells in marrow.

Irrespective of the genomic area affected, when we studied the raw number of lesions more advanced forms of MDS (RAEB-t/AML) were evenly distributed between patients subdivided on sheer number of lesions (0, 1–17, >17). Many hotspots of genomic instability shared between patients were identified. For example, 1p26.3, 10q26 and 4p16 lesions were found in 2 or more patients. Interestingly, these regions contain genes of potential pathologic significance, including tubulin gamma complex associated protein 2 (TUBGCR2) and histone stem-loop binding protein (SLBP). Cryptic lesions on chromosome 7 (e.g. 7p21, 7q31) were identified in 5 patients with normal cytogenetics. These patients suffered from severe cytopenias, consistent with the prognosis of monosomy 7 and highlighting a consensus defect on chromosome 7. Certain chromosomes were rarely or never affected, implying that a more targeted array might be designed for clinical use.

In summary, our study highlights the superior level of resolution of A-CGH as compared to metaphase analysis in the diagnosis of MDS. A prospective analysis is underway to determine the prognostic value of CGH-detected lesions and their pathophysiologic significance.