Family, twin and adoption studies demonstrate that most behavioural phenotypes are influenced by genetic variation and some substantially. This includes phenotypes where environmental influences are thought to be important, including socially influenced behaviours such as the frequency and quantity of alcohol consumption. Laucht et al. (2012) present a study investigating the influences of both environmental measures (parental supervision, involvement and autonomy granting) and genetic effects (COMT Val 158 Met genotype) on drinking behaviour (frequency of drinking and average daily consumption) at the age of 19. After controlling for potential confounding factors including gender, alcohol use at age 15, parental alcohol use disorder, adolescent internalising and externalising symptoms and temperament, they found no main effects of either parental behaviour or COMT genotype on adolescent drinking behaviour. However, they did find evidence of significant Gene · Environment interaction. The pattern of the interaction reported in this study is consistent with the hypothesis of differential susceptibility, which proposes that some individuals by virtue of their genotype are more responsive to environmental influences, whereas others are relatively unresponsive (Ellis, Boyce, Belsky, Bakermans-Kranenburg, & Van Ijzendoorn, 2011). In the example reported here, Laucht and colleagues found that Met/Met homozygotes had either good or bad outcomes, depending on the quality of parental supervision and involvement. In contrast, Val carriers showed no significant effects of the environmental measures on risk for drinking behaviour. These are potentially important findings if it turns out that some individuals are more sensitive to their parenting environment, for better or for worse, when it comes to drinking behaviour. The study conclusions emphasise the need for parents to be aware of the need for appropriate parental supervision and guidance in determining both positive and negative outcomes for their children; but also suggests that this is more important for some individuals than others, depending on underlying genetic and neurobiological factors that lead to differential sensitivity to the parenting environment. The question then arises as to how we would use this information to improve health outcomes? Can we envisage a time when we would use genetic testing as a way to target behavioural strategies towards individual children, or to identify those children for whom we need to pay more attention to environmental risks than others? Given the low predictive power of nearly all genetic findings on behavioural outcomes, we need to be very cautious in presenting such an argument, although if the case was proven for such a mechanism, we might devise a direct (nongenetic) test of environmental sensitivity. However, the strength of the finding may not lie in such direct testing of individual sensitivities to the environment, but rather in the use of genetic data to identify an important environmental effect in the absence of a main effect of the environmental risk, as reported here for the effect of parental supervision on offspring drinking behaviour. This at least estab