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Background: Adults exhibiting severe impulsive and aggressive behaviors have multiple indices of low serotonin (5-HT) neurotransmission. It remains unclear though whether low 5-HT mediates the behavior or instead reflects a pre-existing vulnerability trait. Methodology/Principal Findings: In the present study, positron emission tomography with the tracer alpha-[11C]methyl-Ltryptophan (11C-AMT) was used to compare 5-HT synthesis capacity in two groups of adult males from a 21-year longitudinal study (mean age ± SD: 27.1±0.7): individuals with a history of childhood-limited high physical aggression (CLHPA; N = 8) and individuals with normal (low) patterns of physical aggression (LPA; N = 18). The C-LHPA males had significantly lower trapping of 11C-AMT bilaterally in the orbitofrontal cortex and self-reported more impulsiveness. Despite this, in adulthood there were no group differences in plasma tryptophan levels, genotyping, aggression, emotional intelligence, working memory, computerized measures of impulsivity, psychosocial functioning/adjustment, and personal and family history of mood and substance abuse disorders. Conclusions/Significance: These results force a re-examination of the low 5-HT hypothesis as central in the biology of violence. They suggest that low 5-HT does not mediate current behavior and should be considered a vulnerability factor for impulsive-aggressive behavior that may or may not be expressed depending on other biological factors, experience, and environmental support during development. [ABSTRACT FROM AUTHOR]

Poverty is a well-established risk factor for behavior problems, yet our understanding of putative family mediators during early childhood (i.e., before age 5 years) is limited. The present study investigated whether the association between poverty and behavior problems during early childhood is mediated simultaneously by perceived parenting, family dysfunction and/or maternal depression symptoms. Outcomes measures were high trajectories of physical aggression and hyperactivity between 1.5 and 5 years. Poverty was defined as living 2-4 years below the low-income thresholds defined by Statistics Canada. Using data from the first five rounds of the Quebec Longitudinal Study of Child Development, logistic regressions models showed that poverty was associated with a higher likelihood of being assigned to the high trajectory of physical aggression and hyperactivity. Overprotection and maternal depression symptoms mediated observed associations. Interventions targeting maternal depression, parenting, and poverty should help reducing children's risk for early behavior problems. [ABSTRACT FROM AUTHOR]

Over the past decade, epigenetic analyses have made important contributions to our understanding of healthy development and a wide variety of adverse conditions such as cancer and psychopathology. There is increasing evidence that DNA methylation is a mechanism by which environmental factors influence gene transcription and, ultimately, phenotype. However, differentiating the effects of the environment from those of genetics on DNA methylation profiles remains a significant challenge. Monozygotic (MZ) twin study designs are unique in their ability to control for genetic differences because each pair of MZ twins shares essentially the same genetic sequence with the exception of a small number of de novo mutations and copy number variations. Thus, differences within twin pairs in gene expression and phenotype, including behavior, can be attributed in the majority of cases to environmental effects rather than genetic influence. In this article, we review the literature showing how MZ twin designs can be used to study basic epigenetic principles, contributing to understanding the role of early in utero and postnatal environmental factors on the development of psychopathology. We also highlight the importance of initiating longitudinal and experimental studies with MZ twins during pregnancy. This approach is especially important to identify: (1) critical time periods during which the early environment can impact brain and mental health development, and (2) the specific mechanisms through which early environmental effects may be mediated. These studies may inform the optimum timing and design for early preventive interventions aimed at reducing risk for psychopathology. [ABSTRACT FROM AUTHOR]