Figure I.

Methylation of CpG islands near gene promoters is typically associated with reduced transcription initiation. Although hypomethylated (A) and hypermethylated (C) CpG islands are generally associated with normal and repressed gene expression, respectively, emergent imaging epigenetic work suggests smaller inter-individual variability in the relative methylation level of otherwise hypomethylated CpG islands may also result in phenotypically relevant differences in gene expression (B).