title: Genetic and environmental factors shape infant sleep patterns: a study of 18-month-old twins.
abstract: OBJECTIVE
  Between 25% and 30% of children and adolescents experience sleep disorders. These disorders are complex phenotypes that are regulated by many genes, the environment, and gene-environment interactions. The objective of this study was to evaluate the contribution of genetic and environmental factors to sleep behaviors in early childhood and to contribute to the knowledge on appropriate therapeutic approaches, using a twin design.
  
  
  METHODS
  Data on sleeping behavior were collected from 314 18-month-old twin pairs (127 monozygotic and 187 dizygotic)using a parent-rated questionnaire. We used structural equation modeling to estimate genetic and environmental variance components for different sleep behaviors (cosleeping, sleep duration, and night awakenings).
  
  
  RESULTS
  Shared environment explained almost all (98.3%) of the total variance in cosleeping. Sleep duration was substantially influenced by shared environmental factors (64.1% nocturnal sleep and 61.2% diurnal sleep), with a moderate contribution of additive genetic effects (30.8% and 36.3% for nocturnal and diurnal sleep, respectively). For nocturnal waking episodes, we found a shared environmental contribution of 63.2% and a heritability estimate of 35.3%.
  
  
  CONCLUSIONS
  Most sleep disturbances during early childhood are explained by common shared environmental factors, and behavioral interventions adopted by parents and focused on modifying sleep behavior could contribute to solving sleep disturbances in this age group. However, the influence of genetic factors should not be underestimated, and research in this area could clarify the physiologic architecture of sleeping and contribute to selecting appropriate personalized therapeutic approaches.
authors.affiliation: Istituto Superiore di Sanità, V.le Regina Elena 299, 00161 Rome, Italy. sonia.brescianini@iss.it
authors.forename: Sonia
authors.initials: S
authors.lastname: Brescianini
authors.forename: Anna
authors.initials: A
authors.lastname: Volzone
authors.forename: Corrado
authors.initials: C
authors.lastname: Fagnani
authors.forename: Valeria
authors.initials: V
authors.lastname: Patriarca
authors.forename: Valentina
authors.initials: V
authors.lastname: Grimaldi
authors.forename: Roberta
authors.initials: R
authors.lastname: Lanni
authors.forename: Laura
authors.initials: L
authors.lastname: Serino
authors.forename: Pierpaolo
authors.initials: P
authors.lastname: Mastroiacovo
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Stazi
mesh_terms: D000367:Age Factors; D015331:Cohort Studies; D004777:Environment; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D007558:Italy; D008297:Male; D012016:Reference Values; D012737:Sex Factors; D012894:Sleep Stages / Q000235:genetics* / Q000502:physiology; D012893:Sleep Wake Disorders / Q000453:epidemiology / Q000235:genetics* / Q000503:physiopathology; D011795:Surveys and Questionnaires; D014427:Twins / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics