Moderation of Genetic Influences on Alcohol Involvement by Rural Residency among Adolescents: Results from the 1962 National Merit Twin Study.

Adolescents in rural and urban areas may experience different levels of environmental restrictions on alcohol use, with those in rural areas experiencing greater monitoring and less access to alcohol. Such restrictions may limit expression of genetic vulnerability for alcohol use, resulting in a gene-environment interaction (G × E). This phenomenon has previously been reported in Finnish and Minnesota adolescents. The current study used data from 839 same-sex twin pairs from the 1962 National Merit Scholarship Qualifying Test to determine whether the G × E interaction would be evident in this earlier time period. We also assessed whether the G × E interaction would be moderated by sex, and whether family socioeconomic status (SES; income and parental education) may mediate the G × E interaction. Findings showed the expected interaction among females, with a weaker contribution of genes (2 vs. 44%) and greater contribution of shared environment (62 vs. 29%) to variation in alcohol involvement among rural as compared to urban residents. The G × E interaction was not observed among males, and operated independently from differences in family SES among rural and urban adolescents. This study represents a partial replication in a novel setting of the moderation of the genetic contribution to alcohol use by rural/urban residency, and suggests that SES differences may not explain this effect.