Myelodysplastic syndromes (MDS) are clonal disorders of hematopoietic progenitors characterized by impaired blood cell production due to ineffective hematopoiesis and high propensity to acute myeloid leukemias. One of the prominent features of MDS is the high frequency of unbalanced chromosomal abnormalities that result in genetic imbalances and copy number alterations. Although the chromosomal segments involved in these abnormalities are thought to contain relevant genes to the pathogenesis of MDS, conventional analyses including FISH have failed to identify critical regions small enough to pinpoint their target genes.
Affymetrix® GeneChip® 100K/500K mapping arrays were originally developed for large-scale genotyping of more than 100,000/500,000 SNPs in two separate arrays, but the quantitative nature of the preparative whole-genome amplification and array hybridization thereafter also allows for accurate copy number estimate of the genome using these platforms at the resolutions of 21.3 kb and 5.4 kb with 116,204 and 520,000 oligonucleotide probes, respectively. Here we developed robust algorithms (CNAG) for copy number detection using 100K and/or 500K arrays and analyzed 88 MDS samples on these platforms in order to identify relevant genes for development of MDS.
With these huge numbers of uniformly distributed SNP probes, numerous copy number alterations were sensitively detected in cases with MDS with more numbers of abnormalities found in advanced diseases (RAEB and RAEB-t). In addition to large-scale alterations of various chromosomal segments previously reported in these syndromes, a number of small cryptic chromosomal abnormalities were identified that would escape conventional cytogenetic analysis or array CGH analysis. Minimum overlapping deletions in 5q, 7q, 12p, 13q, and 20q were precisely defined, although no pinpoint homozygous deletions were detected within these regions. A common 20q deletion spans a 400 kb segment harboring five transcriptomes and the common 12p deletion defines a 1.3 Mb region that contains the ETV6 gene. Other common overlapping abnormalities include deletions in 21q22, 17q13, and gains of 11q25. Genome-wide analysis of copy number changes using high-density oligonucleotide arrays provides valuable information about genetic abnormalities in MDS.