title: Genetic and environmental contributions to sleep-wake behavior in 12-year-old twins.
abstract: OBJECTIVE
  To examine the role of genetic and environmental factors on sleep behavior in 12-year-old twins matched for family environment.
  
  
  METHODS
  Population-based twin cohort.
  
  
  METHODS
  Participants were assessed in their home environment.
  
  
  METHODS
  One hundred thirty-two adolescent twins comprising 25 monozygotic (MZ) and 41 dizygotic (DZ) twin pairs; aged 12.2 ± 0.1 y (mean ± standard deviation).
  
  
  METHODS
  N/A.
  
  
  RESULTS
  For 2 weeks in their home environment, participants wore a wrist activity monitor and completed a daily sleep diary. Sleep diaries included reports of bedtime, wake time, and estimated sleep onset time. Mean timing, duration, and quality of sleep during the 2 weeks were calculated for each individual and compared within twin pairs. MZ twin correlations were higher than the DZ correlations for total sleep time (MZr = 0.64; DZr = 0.38) and sleep onset latency (MZr = 0.83; DZr = 0.53) and significantly higher for wake after sleep onset (MZr = 0.66; DZr = 0.04) and sleep efficiency (MZr = 0.82; DZr = 0.10). Univariate modeling showed additive genetic factors accounted for 65% of the variance in total sleep time, 83% in sleep onset latency, and 52% and 57% of the variance in wake after sleep onset and sleep efficiency, respectively. A predominant influence of shared environment was found on the timing of sleep (67% for sleep start time, 86% for sleep end time).
  
  
  CONCLUSIONS
  There is a strong genetic influence on the sleep-wake patterns of 12-year-old adolescents. Genes have a greater influence on sleep initiation and sleep maintenance and a smaller role in sleep timing, likely to be influenced by family environment.
authors.affiliation: School of Psychology and Psychiatry, Monash University, Melbourne, Australia.
authors.forename: Tracey L
authors.initials: TL
authors.lastname: Sletten
authors.forename: Shantha M W
authors.initials: SM
authors.lastname: Rajaratnam
authors.forename: Margaret J
authors.initials: MJ
authors.lastname: Wright
authors.forename: Gu
authors.initials: G
authors.lastname: Zhu
authors.forename: Sharon
authors.initials: S
authors.lastname: Naismith
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Martin
authors.forename: Ian
authors.initials: I
authors.lastname: Hickie
mesh_terms: D056044:Actigraphy; D002648:Child; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D012890:Sleep / Q000235:genetics* / Q000502:physiology; D014427:Twins / Q000235:genetics* / Q000523:psychology; D014429:Twins, Dizygotic / Q000235:genetics / Q000523:psychology; D014430:Twins, Monozygotic / Q000235:genetics / Q000523:psychology; D014851:Wakefulness / Q000235:genetics* / Q000502:physiology
keywords: Adolescence; environmental influences; genetics; heritability; sleep; twins