Genetic and Environmental Influences on Different Components of the Pittsburgh Sleep Quality Index and their Overlap

Study Objectives: To examine the extent to which genetic and environmental factors influence components of sleep quality; the degree to which these components co-occur; and genetic and environmental influences on this co-occurrence. Design: Twin study. Setting: Population based twin registry across the UK. Patients or Participants: Four hundred twenty monozygotic twins, 773 dizygotic twins, and 363 siblings (mode age = 20 years; range 18 to 27 years). Interventions: N/A Measurements and Results: The Pittsburgh Sleep Quality Index (PSQI) assessed 7 components of sleep quality which overlap to varying degrees. Genetic influence on individual components ranged from 0% to 47%. The remaining source of variance was non-shared environment, except for "sleep duration," for which shared environmental influences were important. Phenotypic correlations between components ranged from 0.22 to 0.61. Bivariate analyses indicated substantial overlap between genes influencing phenotypes (10 of 15 correlations were 0.69); and in general, genetic influence accounted for roughly half the association (>40% in 9 of 15 correlations). Non-shared environmental influences were in general less correlated across variables (11 of 15 were < 0.4), but owing to their greater influence on each variable, still accounted for roughly half of each association 40% in 12 of 15 correlations). Conclusions: Genetic and non-shared environmental factors are most important in explaining individual differences with regards to different components of sleep quality, although shared environment may influence sleep duration. The pattern of overlap in the genetic and environmental influences accounting for the associations between components of sleep quality is consistent with that seen in other areas of developmental psychopathology of general genes and specific non-shared environmental influences.