The concept of moderation of the etiology of RSI via PSI has been infrequently tested within a genetically informative framework (50). By relative fit (Akaike’s Information Criterion or AIC), the moderating influences model most parsimoniously explained the relationship between RSI and PSI (AIC of −86.5, compared with AIC=961.2 for correlated influences and AIC=616.6 for the joint model). Moderation of heritable influences (e.g. genes influencing RSI) by PSI represents a (additive) gene x environment interaction (G x E). Such interactions are responsible for variations in the etiology of substance use behaviors – for instance, Dick and colleagues (29) have found that as peer alcohol use increased, heritable factors associated with an adolescent’s own alcohol involvement also increased. Harden et al. (31) provided evidence for both gene by environment correlation – whereby individuals with increased genetic liability for substance use are more likely to affiliate with substance using peers – and for gene by environment interaction, or that the influence of substance using peers was stronger in those individuals who had a high genetic liability to recent alcohol and tobacco use. Most
