Methylation at a given CpG residue is frequently reported as a percent methylated in a given sample, or beta value, with changes at the same location between individuals or groups often reported as a delta beta. Bisulfite pyrosequencing currently has a resolution of approximately 5%–10%, indicating that changes on this order of this magnitude may not be reliably detected. The resolution of array-based technologies such as Illumina’s HumanMethylation450 BeadChip is as precise as 1%–2% for comparison. A key issue for the development of clinically relevant biomarkers will be whether delta betas for a given association are of a sufficient magnitude to provide adequate sensitivity and specificity.
