An epigenomics approach to individual differences and its translation to neuropsychiatric conditions

This review concerns epigenetic mechanisms and their roles in conferring interindividual differences, especially as related to experientially acquired and genetically driven changes in central nervous system (CNS) function. In addition, the review contains commentary regarding the possible ways in which epigenomic changes may contribute to neuropsychiatric conditions and disorders and ways in which epigenotyping might be cross-correlated with clinical phenotyping in the context of precision medicine. The review begins with a basic description of epigenetic marking in the CNS and how these changes are powerful regulators of gene readout. Means for characterizing the individual epigenotype are briefly described, with a focus on DNA cytosine methylation as a readily measurable, stable epigenetic mark. This background enables a discussion of how "epigenotyping" might be integrated along with genotyping and deep phenotyping as a means of implementing advanced precision medicine. Finally, the commentary addresses two exemplars when considering how epigenotype may correlate with and modulate cognitive and behavioral phenotype: schizophrenia and Rett syndrome. These two disorders provide an interesting compare-and-contrast example regarding possible epigenotypic regulation of behavior: whereas Rett syndrome is clearly established as being caused by disruption of the function of an epigenetic "reader" of the DNA cytosine methylome-methyl-CpG-binding protein 2 (MeCP2)-the case for a role for epigenetic mechanisms in schizophrenia is still quite speculative.