title: Are there genetic influences on addiction: evidence from family, adoption and twin studies.
abstract: OBJECTIVE
  In this exciting era of gene discovery, we review evidence from family, adoption and twin studies that examine the genetic basis for addiction. With a focus on the classical twin design that utilizes data on monozygotic and dizygotic twins, we discuss support in favor of heritable influences on alcohol, nicotine, cannabis and other illicit drug dependence.
  
  
  METHODS
  We review whether these genetic factors also influence earlier stages (e.g. experimentation) of the addictive process and whether there are genetic influences specific to each psychoactive substance.
  
  
  RESULTS
  Converging evidence from these studies supports the role of moderate to high genetic influences on addiction with estimates ranging from 0.30 to 0.70. The changing role of these heritable factors as a function of gender, age and cultural characteristics is also discussed. We highlight the importance of the interplay between genes and the environment as it relates to risk for addiction and the utility of the children-of-twins design for emerging studies of gene-environment interaction is presented.
  
  
  CONCLUSIONS
  Despite the advances being made by low-cost high-throughput whole genome association assays, we posit that information garnered from twin studies, especially extended twin designs with power to examine gene-environment interactions, will continue to form the foundation for genomic research.
authors.affiliation: Department of Psychiatry, Washington University School of Medicine, St Louis, MO 63110, USA. arpana@wustl.edu
authors.forename: Arpana
authors.initials: A
authors.lastname: Agrawal
authors.forename: Michael T
authors.initials: MT
authors.lastname: Lynskey
mesh_terms: D000300:Adoption; D017677:Age Distribution; D016739:Behavior, Addictive / Q000235:genetics*; D004200:Diseases in Twins / Q000235:genetics*; D019317:Evidence-Based Medicine; D005190:Family / Q000523:psychology*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006801:Humans; D008297:Male; D012307:Risk Factors; D017678:Sex Distribution; D012931:Social Environment; D019966:Substance-Related Disorders / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics