problems later in life (Kim-Cohen, Caspi, et al., 2006; Caspi, McClay, et al., 2002): Maltreated children who have the genotype that confers high levels of MAOA expression are less likely to develop conduct disorder, antisocial personality, or adult violent crime. In another domain, a common polymorphism of the dopamine transporter gene has been reported to interact with the risk conferred by prenatal exposure to tobacco smoke, leading to increased hyperactive-impulsive and oppositional behaviors in later childhood (Kahn, Khoury, et al., 2003).
In contrast to GxE interactions, gene–environment correlations are genetic influences on variations in the likelihood that an individual will experience specific environmental circumstances (Jaffee and Price, 2007; Rutter and Silberg, 2002; Rutter, Moffitt, and Caspi, 2006). Gene–environment correlations can confound cause and effect and hinder measurement of GxE interactions because a genetically determined behavioral trait can produce a systematic variation in environmental exposure, and that environmental variation can be deemed erroneously to be a cause of a behavioral trait under study (Jaffee and Price, 2007; Lau and Eley, 2008). Children with autism, for example, are chronically and consistently withdrawn from their caregivers. This chronic withdrawal might induce in the caregiver a sense of hopelessness about ever making a deep interpersonal connection with the child, prompting a secondary withdrawal on the part of the caregiver. An