Poster #55 - Sleep and Externalizing Problems in Early Childhood: Shared Environmental and Genetic Underpinnings

• In Event: 1-005 - Poster Session 01
  In Poster Session: PS 01 Section - Developmental Psychopathology

Integrative Statement

Introduction
Sleep problems and externalizing behaviors are related in children and adults (e.g., Aronen et al, 2000), however, little is known about why the two are consistently linked. A handful of genetically-informed studies in adults demonstrates modest genetic overlap between the two (Barclay et al, 2010; Lind et al, 2016), and a study of young children indicates shared environmental overlap between sleep problems and specific behavior problems (e.g., anxiety; Gregory et al, 2004). No research has explored the underlying etiologic links between sleep and the broader externalizing phenotype in childhood. This study examines the genetic and environmental overlap between the two behavioral domains in an early childhood twin sample, at a time when these behaviors are emerging.
Procedure
The sample comprised 623 same-sex twin pairs (MZ=268, DZ=355) assessed within one month of their 3rd birthday. Sleep problems (SP) and externalizing behaviors (EXT) were assessed via parent ratings on the Child Behavior Checklist 1½-5 (CBCL1½-5). No items overlapped across the two scales.
Results and Discussion
SP and EXT were moderately correlated (r=.40, p<.0001). A Bivariate Cholesky model was fit to the data and demonstrated that SP and EXT were highly heritable, explaining 65% and 61% of the overall variance, respectively (Table 1). Shared environmental influences (i.e., experiences that are common to members of a family) were significant but modest (SP c2=.8%; EXT c2=15%), and nonshared environmental factors (i.e., experiences unique to members of a family) were moderate (SP e2=27%; EXT e2=24%). In the best fitting model (Figure 1), there was moderate genetic overlap between the two behavioral domains (rg=.46). These findings are striking similar to research in adults (Barclay et al, 2010; Lind et al, 2016) wherein roughly 80% of the genetic influences on EXT were independent from those on SP (i.e., .48/.61=79%; Table 1) and suggest largely distinct genetic etiologies. In a childhood twin study examining etiologic overlap between sleep and specific behavior problems averaged across ages 3 and 4 years, no genetic overlap was found and shared environmental influences on SP were higher. It is difficult to determine why these differences exist given that they used a measurement that may have increased shared environmental variance (Gregory et al, 2004). Similar to our findings, and in contrast to the adult research, however, is the overlap of the shared environmental influences on SP and EXT (rc=1.00). In other words, though the effect of shared environmental experiences on each was minimal, the common environmental factors that influence sleep are also the same ones that influence externalizing behaviors; for example, family-level chaos or inter-parental conflict. Nonshared environmental influences, as is often the case, were specific to each. Although not included in this abstract, we will also examine etiological sex differences.

Authors

• Megan Flom, Boston University
  Presenting Author

• Jody Ganiban, George Washington University
  Non-Presenting Author

• Kimberly Saudino, Boston University
  Non-Presenting Author