title: Genetic and environmental influences on daytime and nighttime sleep duration in early childhood.
abstract: OBJECTIVE
  To determine the relative contributions of genetic and environmental factors on daytime and nighttime continuous sleep duration at 6, 18, 30, and 48 months of age, and to identify different subgroups of children who followed different daytime and nighttime sleep duration trajectories and to investigate their etiology.
  
  
  METHODS
  The current study included 995 twins (405 monozygotic and 586 dizygotic) of the Quebec Newborn Twin Study recruited from the birth records of the Quebec Statistics Institute. Daytime and nighttime sleep was assessed through maternal reports at 6, 18, 30, and 48 months of age. A semiparametric modeling strategy was used to estimate daytime and nighttime sleep duration trajectories. Quantitative genetic models were used to examine to what extent genetic and environmental factors influenced daytime and nighttime continuous sleep duration.
  
  
  RESULTS
  Genetic modeling analyses revealed environmental influences for all daytime sleep duration trajectories. In contrast, strong genetic influences were found for consolidated nighttime sleep duration (except at 18 months and for the short-increasing sleep duration trajectory).
  
  
  CONCLUSIONS
  This is the first indication that early childhood daytime sleep duration may be driven by environmental settings, whereas the variance in consolidated nighttime sleep duration is largely influenced by genetic factors with a critical environmental time-window influence at ∼18 months.
authors.affiliation: Center for Advanced Research in Sleep Medicine, Sacré-Coeur Hospital, Montreal, Quebec, Canada.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Touchette
authors.forename: Ginette
authors.initials: G
authors.lastname: Dionne
authors.forename: Nadine
authors.initials: N
authors.lastname: Forget-Dubois
authors.forename: Dominique
authors.initials: D
authors.lastname: Petit
authors.forename: Daniel
authors.initials: D
authors.lastname: Pérusse
authors.forename: Bruno
authors.initials: B
authors.lastname: Falissard
authors.forename: Richard E
authors.initials: RE
authors.lastname: Tremblay
authors.forename: Michel
authors.initials: M
authors.lastname: Boivin
authors.forename: Jacques Y
authors.initials: JY
authors.lastname: Montplaisir
mesh_terms: D002675:Child, Preschool; D004777:Environment; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D011792:Quebec; D012890:Sleep / Q000235:genetics* / Q000502:physiology*; D012893:Sleep Wake Disorders / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics
keywords: early childhood; genetic and environmental interplay; sleep duration; twin study