Gene–environment interactions
It is generally accepted that complex disorders such as ADHD
develop as the result of interplay between genetic and environmental
factors (Rutter et al. 2006). Gene–environment interactions
(GxE) offer a plausible explanation as to why some
children show susceptibility to environmental risks while others
are somewhat resilient (Wermter et al. 2010). Although still
in their infancy, exploratory studies are beginning to identify circumstances in which specific genetic variants and environmental
factors interact to heighten risk of ADHD (Nigg et al.
2010). However, despite encouraging early findings, there is
currently a lack of replication in GxE effects and heterogeneity
among trials prevents pooled analysis of effects (Nigg et al.
2010). In addition, genes and environments can overlap in other
ways (gene–environment correlations; rGE). For example, genes
can determine the types of environment a person is exposed to
(including the quality of parenting received), while environmental
experience can also influence gene expression (Rutter
et al. 2006). rGE may therefore manifest as GxE interactions and
future research designs should control for the potential confounding
influences of rGE (Wermter et al. 2010).