Array-Based Comparative Genomic Hybridization for Genome-Wide Analysis of DNA Copy Number in Myelodysplastic Syndromes.

Myelodysplastic syndrome(MDS)is a clonal disorder of hematopoietic stem cells characterized by ineffective hematopoiesis and propensity to acute myeloid leukemias. The conversion of a normal stem cell into a preleukemic and ultimately leukemic state is thought to be a multistep process requiring accumulation of a number of genetic changes. Conventional cytogenetic analysis has disclosed a number of chromosome abnormalities common to MDS and provided valuable clues to characterize these genetic lesions, rarity of balanced translocations and relative predominance of unbalanced abnormalities in MDS, including gene deletions and amplifications. However conventional analytical methods provide only limited resolutions of analysis for identification of genetic gains and losses and prevent further molecular delineation of relevant genes to the pathogenesis of MDS.</PRE>

Array-based comparative genomic hybridization (CGH) is a robust technique to enable rapid and comprehensive genome-wide analysis of genetic aberrations in cancers, in which differentially labeled DNAs from both tumor and normal samples are comparatively hybridized to a large number of genomic DNAs. In this study, we constructed a high-quality array-based CGH system for genome-wide analysis of chromosomal abnormalities to identify candidate target genes of MDS. Our whole genome arrays consisted of 3,300 BAC/PAC clones, thus having an average resolution of 1.0 Mb over the whole human genome. Each clone was amplified with degenerated oligonucleotide primed-PCR (DOP-PCR) and the amplified products were spotted in duplicate grids onto aminosilan-coated glass slides. For more high-resolution analysis, we employed the GeneChip Mapping 100k arrays (Affymetrix), originally developed for large-scale SNP typing, as a tool for detection of copy number changes in selected MDS cases. It contains 116,204 different SNPs on two separate arrays, covering the whole human genome with an average resolution of 21 kb. With this arrays DNA copy number’s changes could be estimated by comparing intensity of SNP signals of tumor cells with that of normal cells from the same patients. In addition, using paired samples from tumor cells and normal cells, large-scale LOH analysis became also possible.</PRE>

In total, 54 MDS samples were analyzed using our array CGH system. In addition to large chromosomal changes, including loss of 5q, 7q, 13q, and 20q, and gain of the whole chromosome 8, a number of small, cryptic chromosomal abnormalities were identified that would escape from conventional cytogenetic detection. Many of these abnormalities were represented only by a single PAC/BAC clone. In several chromosome regions, including 3q13, 5p15, 13p33, and 20q12, there existed commonly deleted regions, which could be confirmed by FISH analysis. Similarly gains of genetic materials were found on 8p23 and 17p13. Several genes were identified within these regions that may be candidates for relevant genes to these genetic alterations. In conclusion, genome-profiling using array CGH techniques were highly useful tools for delineating the pathogenesis of MDS.</PRE>