title: Genetic and environmental contributions to age of onset of alcohol dependence symptoms in male twins.
abstract: OBJECTIVE
  To investigate genetic and environmental influences on the development of specific alcohol dependence symptoms.
  
  
  METHODS
  A classical twin study of 3372 male-male twin pairs in the Vietnam Era Twin (VET) Registry based on telephone interviews about alcohol use.
  
  
  METHODS
  The nine diagnostic symptoms according to the Diagnostic and Statistical Manual of Mental Disorder, version III (revised) (DSM-III-R) definition of alcohol dependence. Symptoms were grouped into those based on impaired control, biological effects and social consequences (Beresford's classification) or early versus late symptoms (Nelson's classification). Survival models with random effects were used to examine the age of onset of each symptom.
  
  
  RESULTS
  Approximately 38% of the variation in age of onset of each symptom group based on Beresford's classification is due to additive genetic factors. The age of onset of late symptoms from Nelson's classification appears to be most affected by genetic factors. Estimates of genetic effects for impaired control symptoms are greatly decreased when twins with comorbid psychiatric disorders are excluded.
  
  
  CONCLUSIONS
  Our results support the heritability of age of onset of DSM-III-R-defined symptoms for alcohol dependence. However, no symptom group in Beresford's classification could be identified as more heritable than other symptom groups. A strong association between genetic vulnerability and co-occurring diseases for symptoms indicative of impaired control could be found. In addition, our findings show that the late symptom group could be a good candidate for subsequent genetic research.
authors.affiliation: Department of Psychiatry, Cardinal Tien Hospital, Taipei, Taiwan. iliu@post.harvard.edu
authors.forename: I-Chao
authors.initials: IC
authors.lastname: Liu
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Blacker
authors.forename: Ronghui
authors.initials: R
authors.lastname: Xu
authors.forename: Garrett
authors.initials: G
authors.lastname: Fitzmaurice
authors.forename: Ming T
authors.initials: MT
authors.lastname: Tsuang
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Lyons
mesh_terms: D000328:Adult; D017668:Age of Onset; D000437:Alcoholism / Q000209:etiology* / Q000235:genetics; D004200:Diseases in Twins / Q000209:etiology* / Q000235:genetics; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D014481:United States