title: Peer deviance, parental divorce, and genetic risk in the prediction of drug abuse in a nationwide Swedish sample: evidence of environment-environment and gene-environment interaction.
abstract: OBJECTIVE
  Peer deviance (PD) strongly predicts externalizing psychopathologic conditions but has not been previously assessable in population cohorts. We sought to develop such an index of PD and to clarify its effects on risk of drug abuse (DA).
  
  
  OBJECTIVE
  To examine how strongly PD increases the risk of DA and whether this community-level liability indicator interacts with key DA risk factors at the individual and family levels.
  
  
  METHODS
  Studies of future DA registration in 1,401,698 Swedish probands born from January 1, 1970, through December 31, 1985, and their adolescent peers in approximately 9200 small community areas. Peer deviance was defined as the proportion of individuals born within 5 years of the proband living in the same small community when the proband was 15 years old who eventually were registered for DA.
  
  
  METHODS
  Drug abuse recorded in medical, legal, or pharmacy registry records.
  
  
  RESULTS
  Peer deviance was associated with future DA in the proband, with rates of DA in older and male peers more strongly predictive than in younger or female peers. The predictive power of PD was only slightly attenuated by adding measures of community deprivation, collective efficacy, or family socioeconomic status. Probands whose parents were divorced were more sensitive to the pathogenic effects of high PD environments. A robust positive interaction was also seen between genetic risk of DA (indexed by rates of DA in first-, second-, and third-degree relatives) and PD exposure.
  
  
  CONCLUSIONS
  With sufficient data, PD can be measured in populations and strongly predicts DA. In a nationwide sample, risk factors at the level of the individual (genetic vulnerability), family (parental loss), and community (PD) contribute substantially to risk of DA. Individuals at elevated DA risk because of parental divorce or high genetic liability are more sensitive to the pathogenic effects of PD. Although the effect of our PD measure on DA liability cannot be explained by standard measures of community or family risk, we cannot, with available data, discriminate definitively between the effect of true peer effects and other unmeasured risk factors.
authors.affiliation: Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond2Department of Psychiatry, Virginia Commonwealth University, Richmond3Department of Human and Molecular Genetics, Virginia Commonwealth University, Richm.
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
authors.affiliation: Center for Primary Health Care Research, Lund University, Malmö, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Ohlsson
authors.affiliation: Center for Primary Health Care Research, Lund University, Malmö, Sweden5Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, California.
authors.forename: Kristina
authors.initials: K
authors.lastname: Sundquist
authors.affiliation: Center for Primary Health Care Research, Lund University, Malmö, Sweden5Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, California.
authors.forename: Jan
authors.initials: J
authors.lastname: Sundquist
mesh_terms: D000293:Adolescent; D000367:Age Factors; D004243:Divorce / Q000523:psychology* / Q000706:statistics & numerical data*; D054541:Family Conflict / Q000523:psychology; D005260:Female; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006801:Humans; D007389:Internal-External Control; D008297:Male; D010379:Peer Group; D011610:Psychosocial Deprivation; D012306:Risk; D012737:Sex Factors; D012931:Social Environment; D012932:Social Facilitation; D012959:Socioeconomic Factors; D013223:Statistics as Topic; D019966:Substance-Related Disorders / Q000235:genetics* / Q000523:psychology*; D013548:Sweden