Similar to GWAS, EWAS are non-hypothesis-driven study approaches. Recently, the EWAS approach was widely applied to study genome-wide DNA methylation alterations associated with a number of diseases including AUDs (Table 3). Two types of DNA methylation microarray platforms were commonly used: one was the Illumina Infinium HumanMethylation27 BeadChip, which covers 27,578 CpG sites located in the proximal promoter regions of 14,475 annotated genes (including 110 microRNA genes), and another was the Illumina Infinium HumanMethylation450 BeadChip, which covers 487,557 CpGs across the genome and includes 94% of the Illumina Infinium HumanMethylation27 BeadChip probes.
