To quantitatively detect hypermethylation and to analyze methylation pattern, a methylation-specific oligonucleotide microarray for quantitative analysis was developed. The method used bisulfite-modified DNA as a template for PCR amplification, resulting in conversion of unmethylated cytosine, but not methylated cytosine, into thymine within CpG islands of interest. The amplified product, therefore, may contain a pool of DNA fragments with altered nucleotide sequences due to differential methylation status. A test sample was hybridized to a set of oligonucleotide arrays that discriminate methylated and unmethylated cytosine at specific nucleotide positions,and quantitative differences in hybridization were determined by fluorescence analysis. Four clinical samples of gastric cancer were quantitatively detected and methylation pattern of five methylated clones were analyzed with the methylation-specific oligonucleotide microarray. The results of microarray hybridization were in agreement with bisulfite genomic DNA sequencing. It showed that methylation-specific oligonucleotide microarray for quantitative analysis is a promising technique for mapping methylation changes in multiple CpG island loci and for generating epigenetic profiles in cancer.
