Table 2.

Definition of Common Terms Used in Epigenetics Research

Term	Definition
Epigenome-Wide Association Study (EWAS)	A comprehensive genome-wide testing of epigenetic marks and how they are associated with phenotypes or exposures of interest
CpG Site	DNA dinucleotides of cytosine followed by guanine in which the cytosine nucleotide may have a methyl group added by DNA methyltransferase, which can alter gene transcription
Differentially Methylated Region (DMR)	An entire genomic region composed of multiple CpG sites with differential DNA methylation across samples
Non-coding RNAs	Functional molecules of RNA that are not translated to proteins but can affect gene expression and protein functioning
Epigenetic Clocks	Statistical calculators that use methylation data at certain CpG sites to derive an epigenetic age, which is a marker of biological aging that is correlated with morbidity and mortality
Epigenetic Age Acceleration (EAA)	Deviations between epigenetic and chronological age calculated as the residuals from when each DNA methylation clock output is regressed on the chronological age of each participant
Methylation Euantitative Trait Loci (meQTL)	Single-nucleotide polymorphisms (SNPs) associated with DNA methylation variation of a CpG site