title: The causes of parent-offspring transmission of drug abuse: a Swedish population-based study.
abstract: BACKGROUND
  While drug abuse (DA) is strongly familial, we still have limited knowledge about the causes of its cross-generational transmission.
  
  
  METHODS
  We examined DA ascertained from national registers in offspring of three family types from the Swedish population [intact (n = 2,111,074), 'not-lived-with' (n = 165,315, where biological parents never lived with their offspring) and 'step' (n = 124,800 offspring)], which reflected, respectively, the effects of genes + rearing, genes only and rearing only. We replicated these results in three high-risk co-relative designs.
  
  
  RESULTS
  Combined across mothers and fathers, the hazard ratio (HR) for DA in offspring given DA in parents was 3.52 in intact, 2.73 in 'not-lived-with' and 1.79 in stepfamilies. In 968 biological full or half-sibling pairs one of whom was reared by and the other never lived with their parent with DA, the HR for DA was greater in the reared than 'not-lived-with' child (HR 1.57). In 64 offspring pairs of a parent with DA, the HR for DA was greater in a reared biological v. step-parented non-biological child (HR 3.33). In 321 pairs of offspring of a parent with DA one of whom was a not-lived-with biological child and the second a step-parented non-biological child, the HR for DA was greater in the biological v. stepchild (HR 1.80).
  
  
  CONCLUSIONS
  Both genetic and environmental factors contribute substantially to parent-offspring resemblance for DA. The general population contains informative family constellations that can complement more traditional adoption designs in clarifying the sources of parent-offspring resemblance.
authors: Virginia Institute for Psychiatric and Behavioral Genetics,Virginia Commonwealth University,Richmond, VA,USA.
authors: K S
authors: KS
authors: Kendler
authors: Center for Primary Health Care Research,Lund University,Malmö,Sweden.
authors: H
authors: H
authors: Ohlsson
authors: Center for Primary Health Care Research,Lund University,Malmö,Sweden.
authors: K
authors: K
authors: Sundquist
authors: Center for Primary Health Care Research,Lund University,Malmö,Sweden.
authors: J
authors: J
authors: Sundquist
mesh_terms: D000293:Adolescent; D000300:Adoption; D002648:Child; D002668:Child Rearing / Q000523:psychology*; D002675:Child, Preschool; D005190:Family / Q000523:psychology; D005260:Female; D059647:Gene-Environment Interaction; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D010287:Parent-Child Relations; D016016:Proportional Hazards Models; D012042:Registries; D012307:Risk Factors; D012931:Social Environment; D019966:Substance-Related Disorders / Q000209:etiology* / Q000235:genetics; D013548:Sweden