title: Testing gene × environment moderation of tobacco and marijuana use trajectories in adolescence and young adulthood.
abstract: OBJECTIVE
  This study examines the main and interaction effects of known social risk factors for substance use (inadequate parental monitoring and substance using friends) in adolescence and a polygenic score in predicting marijuana and tobacco use in adolescence and young adulthood.
  
  
  METHODS
  Phenotypic and genetic data were derived from a longitudinal study of a cohort of urban, predominately African American youth. Last year substance-use measures were collected annually from 8th grade through age 22. Participant self-reports of substance-using friends and parent monitoring were obtained yearly from Grades 8 to 12. Using longitudinal latent class analysis, the authors identified parallel developmental trajectories of tobacco and marijuana use and parent monitoring and the proportion of substance-using friends.
  
  
  RESULTS
  Two trajectories were identified for tobacco and marijuana use, characterized by moderate versus little-to-no use. Additionally, 2 latent profiles were found for the social environment profiles: those characterized by higher parent monitoring and a lower proportion of substance-using friends versus lower parent monitoring and a higher proportion of substance-using friends.
  
  
  CONCLUSIONS
  We found main and interaction effects for the polygenic score and social environment profile in predicting the longitudinal classes of marijuana and tobacco use. With respect to the interaction effect, membership in the moderate-use classes of marijuana and tobacco use was highest among those in the social environment profile characterized by lower parent monitoring and a higher proportion of substance-using friends.
authors.affiliation: Department of Mental Health, Bloomberg School of Public Health, Johns Hopkins University.
authors.forename: Rashelle J
authors.initials: RJ
authors.lastname: Musci
authors.affiliation: Molecular Neurobiology Branch, National Institute on Drug Abuse Intramural Research Program, National Institutes of Health.
authors.forename: George
authors.initials: G
authors.lastname: Uhl
authors.affiliation: Department of Mental Health, Bloomberg School of Public Health, Johns Hopkins University.
authors.forename: Brion
authors.initials: B
authors.lastname: Maher
authors.affiliation: Department of Mental Health, Bloomberg School of Public Health, Johns Hopkins University.
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Ialongo
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D001741:Black or African American / Q000706:statistics & numerical data; D015142:Baltimore / Q000453:epidemiology; D002648:Child; D015331:Cohort Studies; D005260:Female; D059647:Gene-Environment Interaction; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008385:Marijuana Smoking / Q000453:epidemiology*; D012931:Social Environment; D064424:Tobacco Use / Q000453:epidemiology*; D014505:Urban Population / Q000706:statistics & numerical data; D055815:Young Adult