Non-imprinted epigenetics in fetal and postnatal development and growth.

Recent evidence demonstrates that the environment in early life can have important effects on fetal and postnatal growth, on development and on risk of developing common non-communicable diseases in later life. In animals, the environment during early life induces altered phenotypes in ways which are influenced or mediated by epigenetic mechanisms. The latter include DNA methylation, covalent modifications of histones and non-coding RNAs. Most is known about DNA methylation changes, which are gene specific, include effects on non-imprinted genes and function at the level of individual CpG dinucleotides to alter gene expression. Preliminary evidence from human studies suggests a similar important role for epigenetic processes. Tuning of phenotype by the developmental environment has adaptive value because it attempts to match an individual's responses to the environment predicted to be experienced later; hence, such processes have been selected during evolution as conferring fitness advantage. When the phenotype is mismatched, e.g. from inaccurate nutritional cues from the mother or placenta before birth, or from rapid environmental change through improved socioeconomic conditions, risk of non-communicable diseases increases. Evidence is accruing that endocrine or nutritional interventions during early postnatal life can reverse epigenetic and phenotypic changes induced, for example, by unbalanced maternal diet during pregnancy. Elucidation of epigenetic processes may enable early intervention strategies to improve early development and growth.