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

Area of Science:

• Behavioral Genetics
• Developmental Psychology
• Psychopathology

Background:

• Internalizing and externalizing behavior problems are significant risk factors for adult psychopathology.
• Existing heritability estimates for these behaviors vary widely, often limited by reliance on twin data and other-reports.

Purpose of the Study:

• To investigate genetic and environmental influences on problem behavior using a Nuclear Twin Family Design and self-reports.
• To address limitations of previous twin studies and clarify the interplay of genes and environment.

Main Methods:

• Analysis of 3,087 twin pairs (aged 11-23), siblings, and parents using structural equation modeling.
• Estimation of heritability for internalizing and externalizing behaviors across three twin birth cohorts.
• Utilized a Nuclear Twin Family Design with self-report data.

Main Results:

• Genetic influences account for approximately one-third of the variance in both internalizing and externalizing behaviors.
• Shared environmental influences were identified only for internalizing behaviors and found to be twin-specific.
• Heritability estimates from classic twin designs may be overestimated, suggesting a greater role for environmental influences.

Conclusions:

• Environmental influences play a more substantial role in behavior problems than previously suggested.
• Family-specific environmental influences appear to have a lesser impact than initially assumed or operate on an individual level.
• Findings contribute to understanding the 'missing heritability problem' by highlighting potential overestimation in traditional twin studies.