title: The rearing environment and risk for drug abuse: a Swedish national high-risk adopted and not adopted co-sibling control study.
abstract: BACKGROUND
  Although drug abuse (DA) is strongly familial, with important genetic influences, we need to know more about the role of rearing environment in the risk for DA. To address this question, we utilized a high-risk adopted and non-adopted co-sibling control design.
  
  
  METHODS
  High-risk offspring had one or more biological parents registered for DA, alcohol use disorders or criminal behavior. Using Swedish registries, we identified 1161 high-risk full-sibships and 3085 high-risk half-sibships containing at least one member who was adopted-away and one member who was not. Registration for DA was via national criminal, medical and pharmacy registers. In Sweden, adoptive families are screened to provide high-quality rearing environment for adoptees.
  
  
  RESULTS
  Controlling for parental age at birth and gender (and, in half-siblings, high-risk status of the other parent), risk for DA was substantially lower in the full- and half-siblings who were adopted v. not adopted [hazard ratios and 95% confidence intervals: 0.55 (0.45-0·69) and 0.55 (95% CI 0.48-0.63), respectively]. The protective effect of adoption on risk for DA was significantly stronger in the full- and half-sibling pairs with very high familial liability (two high-risk parents) and significantly weaker when the adoptive family was broken by death or divorce, or contained a high-risk parent.
  
  
  CONCLUSIONS
  In both full- and half-sibling pairs, we found replicated evidence that rearing environment strongly impacts on risk for DA. High-quality rearing environments can substantively reduce risk for DA in those at high genetic risk.
authors.affiliation: Virginia Institute for Psychiatric and Behavioral Genetics,Virginia Commonwealth University,Richmond,VA,USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Kendler
authors.affiliation: Center for Primary Health Care Research,Lund University,Malmö,Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Ohlsson
authors.affiliation: Center for Primary Health Care Research,Lund University,Malmö,Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Sundquist
authors.affiliation: Center for Primary Health Care Research,Lund University,Malmö,Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Sundquist
mesh_terms: D000293:Adolescent; D000300:Adoption; D000328:Adult; D002648:Child; D002668:Child Rearing; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010290:Parents; D012042:Registries / Q000706:statistics & numerical data*; D012307:Risk Factors; D035781:Siblings; D019966:Substance-Related Disorders / Q000453:epidemiology / Q000209:etiology*; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: Adoption; cross-generational transmission; drug abuse; rearing