that methylation of OXTR would be greater for those initiating early substance use to the extent they also carried the “s” allele, but would be less for those protected against early substance use initiation by participation in SAAF, or who were LL homozygotes. Thus, we expected that the pattern would highlight a significant indirect effect of SAAF on OXTR methylation among “s” allele carriers only, leading to a significantly moderated pattern of mediation. Differential methylation for those facing different environmental circumstance follows a general pattern in which behavioral traits are modified by experience to better fit with environmental demands (Landecker and Panofsky, 2013; Meloni, 2014; Simons & Klopack, 2015), a pattern that may be more pronounced for some environmental effects among carriers of the “s” allele of the 5-HTTLPR (Beach et al., 2014).
