Abstract
This review summarizes current knowledge and outlines future directions relevant to questions concerning environmental epigenetics and the processes that contribute to temperament development. Links between prenatal adversity, epigenetic programming, and early manifestations of temperament are important in their own right, also informing our understanding of biological foundations for social-emotional development. In addition, infant temperament attributes represent key etiological factors in the onset of developmental psychopathology, and studies elucidating their prenatal foundations expand our understanding of developmental origins of health and disease. Prenatal adversity can take many forms, and this overview is focused on the environmental effects of stress, toxicants, substance use/psychotropic medication, and nutrition. Dysregulation associated with attention-deficit/hyperactivity-disruptive disorders was noted in the context of maternal substance use and toxicant exposures during gestation, as well as stress. Although these links can be made based on the existing literature, currently few studies directly connect environmental influences, epigenetic programming, and changes in brain development/behavior. The chain of events starting with environmental inputs and resulting in alterations to gene expression, physiology, and behavior of the organism is driven by epigenetics. Epigenetics provides the molecular mechanism of how environmental factors impact development and subsequent health and disease, including early brain and temperament development.
Highlights
Considerable evidence points to the importance of in utero environmental exposures in shaping offspring temperament development, with epigenetic mechanisms conferring the risk, as indicated by the environmental epigenetics perspective. Greater understanding of these connections is critical for advancing developmental origins of health and disease (DOHaD) research and for elucidating prenatal origins of developmental psychopathology, which could lead to more effective preventative efforts
Research that starts with environmental adversities and considers epigenetic alterations as well as brain/behavior effects related to temperament has been limited to date
Animal studies provide an opportunity to directly manipulate independent variables related to environmental exposure, ensuring internal validity, yet their external validity with respect to human applications is necessarily limited
Summary
DNA methylation occurs when a small (methyl) chemical group is attached to the DNA base cytosine (C) in a cytosine nucleotide–phosphate–guanine nucleotide (CpG) sequence. Covalent modification of DNA by methylation of cytosine residues serves to alter transcription and genome activity. DNA methylation is responsible for silencing of transposable elements and pericentromeric repeats to ensure genome integrity (Chen, Tsujimoto, & Li, 2004; Kaneko-Ishino & Ishino, 2010; Xu, Bai, Collins, & Ghishan, 1999), inactivation of the X-chromosome (Lock, Takagi, & Martin, 1987; Sado, Okano, Li, & Sasaki, 2004), and genomic imprinting & Khosla, 1999; Reik, Collick, Norris, Barton, & Surani, 1987). Critical to multiple developmental outcomes, DNA methylation is emerging as important for temperament development (e.g., Fuemmeler et al, 2016)
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