a1 Washington University, St Louis, Missouri, United States of America. firstname.lastname@example.org
a2 Washington University, St Louis, Missouri, United States of America.
a3 Indiana University, Bloomington, United States of America.
a4 Whitehead Institute, MIT, Massachusetts, United States of America.
a5 University of Helsinki and National Public Health Institute, Helsinki, Finland.
a6 University of Jyväskylä, Finland.
a7 Indiana University, Bloomington, United States of America.
In contrast to many phenotypes that have been studied using twin designs, substance use shows considerable evidence of environmental influence. Accordingly, specifying the relevant environments and understanding the nature of their effects is an important research priority. Twin studies also have demonstrated that the importance of genetic and environmental influences varies across development for a variety of behavioral outcomes, including substance use. Here, we report analyses exploring moderating effects associated with parenting and peer characteristics on adolescent smoking and drinking, measured at ages 14 and 17. We find significant evidence of moderating effects associated with two dimensions of parenting (parental monitoring and time spent in activities with parents) on adolescent smoking, measured at two time points across development, but no moderating effects on adolescent drinking. Genetic influences on smoking increased, and common environmental effects decreased, as adolescents reported less parental monitoring and spending more time with their parents. Conversely, we find evidence that adolescent drinking is more strongly influenced by peer characteristics. The importance of genetic predispositions was increased among adolescents who reported more friends who used alcohol. These analyses illustrate the importance of incorporating measured aspects of the environment into genetically informative twin models to begin to understand how specific environments are related to various outcomes. Furthermore, they illustrate the importance of using a developmental perspective to understand how specific influences may vary across different ages, and across different phenotypes.
(Received November 06 2006)
(Accepted January 29 2007)
c1 Address for correspondence: Danielle M. Dick, Washington University in St Louis, Department of Psychiatry, Box 8134, 660 South Euclid Ave, St. Louis, MO 63110, USA.