title: Replication of the Stockholm Adoption Study of alcoholism. Confirmatory cross-fostering analysis.
abstract: BACKGROUND
  Two forms of alcoholism with distinct clinical features and mode of inheritance were first distinguished in the Stockholm Adoption Study. This involved a large sample of children born in Stockholm, Sweden, who were adopted at an early age and reared by nonrelatives. Type 1 alcoholism had adult onset and rapid progression of dependence without criminality, whereas type 2 had teenage onset of recurrent social and legal problems from alcohol abuse.
  
  
  METHODS
  A replication study was carried out with 577 men and 660 women born in Gothenburg, Sweden, and adopted at an early age/by nonrelatives. The genetic and environmental backgrounds of the adoptees were classified by the exact procedures calibrated by discriminant analysis in the original study.
  
  
  RESULTS
  Both type 2 and severe type 1 alcoholism were confirmed as independently heritable forms of alcoholism in male adoptees. The lifetime risk of severe alcoholism was increased 4-fold in adopted men with both genetic and environmental risk factors characteristic of type 1 alcoholism compared with the others (11.4% vs 3.0%). Neither genetic nor environmental risk factors for type 1 alcoholism by themselves were sufficient to cause alcoholism. In contrast, the risk of type 2 alcoholism was increased 6-fold in adopted sons with a type 2 genetic background compared with others; regardless of their postnatal environment (10.7% vs 2.0%). The sons with a type 2 genetic background in the replication sample had no excess of type 1 alcoholism, and vice versa. There was no increased risk of mild abuse in adopted men regardless of their genetic or environmental background.
  
  
  CONCLUSIONS
  Type 1 and type 2 alcoholism are clinically distinct forms of alcoholism with causes that are independent but not mutually exclusive.
authors.affiliation: Department of Social Medicine, University of Umeå, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Sigvardsson
authors.forename: M
authors.initials: M
authors.lastname: Bohman
authors.forename: C R
authors.initials: CR
authors.lastname: Cloninger
mesh_terms: D000300:Adoption; D000328:Adult; D017668:Age of Onset; D000428:Alcohol Drinking / Q000235:genetics; D000437:Alcoholism / Q000145:classification / Q000453:epidemiology / Q000235:genetics*; D016241:Child of Impaired Parents / Q000706:statistics & numerical data; D016002:Discriminant Analysis; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D008875:Middle Aged; D009679:Nuclear Family; D016017:Odds Ratio; D010551:Personality / Q000235:genetics; D012042:Registries; D015203:Reproducibility of Results; D012307:Risk Factors; D012720:Severity of Illness Index; D012737:Sex Factors; D012923:Social Class; D012931:Social Environment; D013548:Sweden / Q000453:epidemiology