title: Timing of menarche and the origins of conduct disorder.
abstract: BACKGROUND
  Precocious onset of menses (ie, age < or =11 years) has repeatedly been identified as a risk factor for higher rates of delinquency or conduct disorder (CD) in girls. Although this association is often conceptualized as environmentally mediated (via processes such as affiliation of early-menstruating youth with older, more deviant peers), such conclusions are premature as biological and genetic explanations have yet to be fully considered.
  
  
  OBJECTIVE
  To uncover the origins of the association between CD and timing of menarche.
  
  
  METHODS
  The sample consisted of a population-based birth cohort of 708 mid-adolescent female twins assessed as part of the ongoing Minnesota Twin Family Study. We conducted 2 sets of analyses: standard bivariate analyses to uncover possible common genes and moderator analyses to evaluate possible moderation of genetic influences on CD by timing of menarche.
  
  
  METHODS
  Conduct disorder was assessed via individual semistructured interviews with mothers and adolescents. Menarcheal status and age at menarche were assessed via the Pubertal Development Scale.
  
  
  RESULTS
  The results argued against common genetic influences but did provide evidence of etiological moderation of CD by timing of menarche. The heritability of CD was strongest (67%) in girls with average timing of menarche (ie, age 12-13 years) and substantially weaker (8%) in those with early onset. Those with late initiation of menses (ie, age >13 years) similarly exhibited weaker genetic influences (29%). Shared environmental influences showed the opposite pattern, as they were far stronger for those with precocious and delayed onset vs those with average onset.
  
  
  CONCLUSIONS
  Our findings provide indirect support for psychosocial interpretations of the impact of precocious menarche and, to a lesser extent, delayed menarche on CD development. Further, they lend support to the notion that in some cases, genetic influences on psychopathology may be strongest in the "average, expectable" environment.
authors.affiliation: Department of Psychology, Michigan State University, East Lansing, MI 48824, USA. burts@msu.edu
authors.forename: S Alexandra
authors.initials: SA
authors.lastname: Burt
authors.forename: Matt
authors.initials: M
authors.lastname: McGue
authors.forename: Janeen A
authors.initials: JA
authors.lastname: DeMarte
authors.forename: Robert F
authors.initials: RF
authors.lastname: Krueger
authors.forename: William G
authors.initials: WG
authors.lastname: Iacono
mesh_terms: D000367:Age Factors; D002648:Child; D015331:Cohort Studies; D019955:Conduct Disorder / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D004200:Diseases in Twins / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008572:Menarche / Q000235:genetics / Q000502:physiology*; D009035:Mothers / Q000523:psychology / Q000706:statistics & numerical data; D011569:Psychiatric Status Rating Scales; D011629:Puberty, Precocious / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D012307:Risk Factors; D012931:Social Environment