title: Associations between sleep-wake consolidation and language development in early childhood: a longitudinal twin study.
abstract: OBJECTIVE
  The objectives were (1) to assess associations between sleep consolidation at 6, 18 and 30 months and language skills at 18, 30, and 60 months; and (2) to investigate the genetic/environmental etiology of these associations.
  
  
  METHODS
  Longitudinal study of a population-based twin cohort.
  
  
  METHODS
  1029 twins from the Quebec Newborn Twin Study.
  
  
  RESULTS
  Sleep consolidation was derived from parental reports of day/night consecutive sleeping durations. Language skills were assessed with the MacArthur Communicative Development Inventory at 18 and 30 months and the Peabody Picture Vocabulary Test at 60 months. The day/night sleep ratio decreased significantly from 6 to 30 months. The 6- and 18-month ratios were negatively correlated with subsequent language skills. Children with language delays at 60 months had less mature sleep consolidation at both 6 and 18 months than children without delays and those with transient early delays. Genetic and regression analyses revealed that the sleep ratio at 6 months was highly heritable (64%) and predicted 18-month (B = -0.06) and 30-month language (B = -0.11) mainly through additive genetic influences (R(Gs) = 0.32 and 0.33, respectively). By contrast, the sleep ratio at 18 months was mainly due to shared environment influences (58%) and predicted 60-month language (B = -0.08) through shared environment influences (R(Cs) = 0.24).
  
  
  CONCLUSIONS
  Poor sleep consolidation during the first 2 years of life may be a risk factor for language learning, whereas good sleep consolidation may foster language learning through successive genetic and environmental influences.
authors.affiliation: Research Unit on Children’s Psychosocial Maladjustment, Montreal, Canada. Ginette.Dionne@psy.ulaval.ca
authors.forename: Ginette
authors.initials: G
authors.lastname: Dionne
authors.forename: Evelyne
authors.initials: E
authors.lastname: Touchette
authors.forename: Nadine
authors.initials: N
authors.lastname: Forget-Dubois
authors.forename: Dominique
authors.initials: D
authors.lastname: Petit
authors.forename: Richard E
authors.initials: RE
authors.lastname: Tremblay
authors.forename: Jacques Y
authors.initials: JY
authors.lastname: Montplaisir
authors.forename: Michel
authors.initials: M
authors.lastname: Boivin
mesh_terms: D000367:Age Factors; D000704:Analysis of Variance; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D007804:Language Development; D008137:Longitudinal Studies; D008297:Male; D011792:Quebec; D012890:Sleep / Q000235:genetics* / Q000502:physiology; D014427:Twins / Q000235:genetics*