title: Sleep reactivity and insomnia: genetic and environmental influences.
abstract: OBJECTIVE
  Determine the genetic and environmental contributions to sleep reactivity and insomnia.
  
  
  METHODS
  Population-based twin cohort.
  
  
  METHODS
  1782 individual twins (988 monozygotic or MZ; 1,086 dizygotic or DZ), including 744 complete twin pairs (377 MZ and 367 DZ). Mean age was 22.5 ± 2.8 years; gender distribution was 59% women.
  
  
  METHODS
  Sleep reactivity was measured using the Ford Insomnia Response to Stress Test (FIRST). The criterion for insomnia was having difficulty falling asleep, staying asleep, or nonrefreshing sleep "usually or always" for ≥ 1 month, with at least "somewhat" interference with daily functioning.
  
  
  RESULTS
  The prevalence of insomnia was 21%. Heritability estimates for sleep reactivity were 29% for females and 43% for males. The environmental variance for sleep reactivity was greater for females and entirely due to nonshared effects. Insomnia was 43% to 55% heritable for males and females, respectively; the sex difference was not significant. The genetic variances in insomnia and FIRST scores were correlated (r = 0.54 in females, r = 0.64 in males), as were the environmental variances (r = 0.32 in females, r = 0.37 in males). In terms of individual insomnia symptoms, difficulty staying asleep (25% to 35%) and nonrefreshing sleep (34% to 35%) showed relatively more genetic influences than difficulty falling asleep (0%).
  
  
  CONCLUSIONS
  Sleep reactivity to stress has a substantial genetic component, as well as an environmental component. The finding that FIRST scores and insomnia symptoms share genetic influences is consistent with the hypothesis that sleep reactivity may be a genetic vulnerability for developing insomnia.
authors: Henry Ford Hospital, Sleep Disorders and Research Center, Detroit, Michigan 48202, USA. cdrake1@hfhs.org
authors: Christopher L
authors: CL
authors: Drake
authors: Naomi P
authors: NP
authors: Friedman
authors: Kenneth P
authors: KP
authors: Wright
authors: Thomas
authors: T
authors: Roth
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D004200:Diseases in Twins; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D007319:Sleep Initiation and Maintenance Disorders / Q000235:genetics*; D013312:Stress, Physiological; D013315:Stress, Psychological / Q000150:complications; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D014851:Wakefulness / Q000235:genetics*; D055815:Young Adult