Enhancers are cis-regulatory elements that enable precise spatiotemporal 
patterns of gene expression during development and are notable for being able to 
function at large distances from their target genes. Such regulatory elements 
often bypass intervening genes and typically comprise binding sites for multiple 
transcription factors that can also be transcribed by RNA polymerase II (Pol II) 
to produce noncoding enhancer RNAs (eRNAs). Genome-wide analyses have revealed 
chromatin signatures of enhancers, such as the enrichment for monomethylation of 
histone H3 lysine 4 (H3K4me1) and the acetylation or methylation of histone H3 
lysine 27 (H3K27). Enhancer signatures have been used to describe the 
transitions of these regulatory elements from inactive to primed and from 
activated to decommissioned states during development. New mutations of enhancer 
sequences and of the protein factors regulating enhancer function in human 
disease continue to be identified, contributing to a growing class of 
'enhanceropathies'.