Six studies have examined whether the 5-HTTLPR polymorphism (L and S variants, LL, LS and SS genotypes) interacts with environmental risk factors to predict drinking outcomes. These studies are reviewed in chronological order starting with positive GxE findings. In the first study, young Swedish adults who had the LS genotype and neutral or poor family relationships were more likely to drink until they were intoxicated (89–90%) than those with other combinations of genotypes and family relationship quality (range 39–67%) (Nilsson et al., 2005). A similar pattern of GxE was found for quantity of alcohol consumption. In a study of maltreated children and matched community controls aged 8 to 16 (Kaufman et al., 2007), individuals with the LS and SS genotypes with exposure to maltreatment were at a greater risk for alcohol initiation (33%) compared to those not exposed to maltreatment (8%), and those with the LL genotype with or without a history of maltreatment (24% and 0%, respectively). It is noteworthy that none of the children with the SS genotype had initiated alcohol consumption, and similar to findings reported by Nilsson et al. (2005), the GxE associated with the S variant was attributable to the LS genotype.
