On the etiology of internalizing and externalizing problem behavior: A twin-family study

Abstract

Internalizing and externalizing behavior problems are established risk factors for many unpleasant outcomes and psychopathology in adulthood, and understanding the interplay between genes and environment is important for deducing implications for therapeutic interventions. Among genetic studies on internalizing and externalizing problem behavior, the heritability estimates differ widely. Most research only uses twin data and other-reports, and therefore certain limitations are inevitable. Our study is the first to investigate genetic and environmental influences on problem behavior using a Nuclear Twin Family Design and self-reports, in order to address these limitations. Internalizing and externalizing problem behavior of 3,087 twin pairs (age 11-23), a sibling, and their parents were analyzed with structural equation modeling to estimate heritability separately for each of three twin birth cohorts. Genetic influences account for about one-third of the variance for both internalizing and externalizing. Shared environmental influences were only found for internalizing, and through the advantages of considering data from the whole twin family, firstly could be identified as solely twin-specific. Our findings could contribute to a better understanding of the gap between heritability based on twin studies and DNA-based heritability ('missing heritability problem'): Results indicate that heritability estimates gained via classic twin design and other-reports are slightly overestimated and therefore environmental influences, in general, are more important than previous research suggests. Simultaneously, we showed that family-specific environment either contributes to behavior problems only on an individual level, or that it has a lesser influence than originally thought.

Integrative analysis of genomic and exposomic influences on youth mental health

“…We initially found that genome‐wide influences explained more than twice the variance in externalizing symptoms (19%) compared to internalizing symptoms (6%) at this age. This aligns with twin‐based literature, indicating externalizing symptoms are more heritable than internalizing symptoms in early adolescence (Bergen, Gardner, & Kendler, 2007 ; Nikstat & Riemann, 2020 ) – potentially due to measurement, as externalizing behaviors are more easily observed and potentially captured with reduced noise (Bartels et al., 2004 ), or life course timing, since depression and other internalizing conditions may onset later in adolescence and young adulthood (Nivard et al., 2017 ). Unlike twin studies that extrapolate genetic and environmental influences based on inherited similarities/differences, we examined common genomic variation in unrelated individuals.…”

“…Broadly speaking, it is known that both genetic and environmental factors play a role in influencing mental health among youth (Kwong et al., 2019 ; Nikstat & Riemann, 2020 ). However, a complete picture remains obscured by the limited focus of prior studies.…”

Polygenic risks for joint developmental trajectories of internalizing and externalizing problems: findings from the ALSPAC cohort

“…Whereas demographic, perinatal, child dispositional, and family and broader social environmental predictors of joint internalizing/externalizing developmental trajectories have been studied, the role of genetic predisposition to mental health problems has only been indirectly considered through parental history of psychiatric illness. Yet, the heritability for both internalizing and externalizing difficulties is estimated to be above 30% (Nikstat & Riemann, 2020) and for externalizing difficulties as high as 80% (Hicks, Krueger, Iacono, McGue, & Patrick, 2004). The genetic architecture of internalizing and externalizing difficulties is complex with hundreds to thousands of genes contributing to their heritability and individual risk alleles typically only having very small effects.…”

An Introduction to the Special Issue: Developmental Behavior Genetics and Externalizing Psychopathology

“…Parent rating assimilation and contrast biases for various child behaviors have been demonstrated for monozygotic (MZ) and dizygotic (DZ) pairs, respectively (Bartels et al 2004;Saudino 2003). Self-reports also are prone to social report biases (Nikstat and Riemann 2020), as in all research. Court records may reflect social or cultural biases (Ahonen et al 2017;Stevens and Morash 2015).…”