This array allows interrogating the methylation status of 27,578 highly informative CpG sites located in the proximal promoters of 14,475 protein coding genes. This corresponds to an average of two interrogated CpGs per genes although a subset of more than 200 cancer-related genes has 3-20 interrogated CpGs. The Infinium assay uses a pair of probes for every CpG, with one probe measuring the level of the methylated CpG and the other probe measuring the level of the unmethylated CpG. The methylation of the CpG is then often expressed as a beta value, which is the ratio of the methylated signal on the sum of the methylated and unmethylated signal. Thus, beta values vary from 0.0 for a fully unmethylated CpG to 1.0 for a fully methylated CpG. These data are available for 34 patients from the TOP trial.
