Genetic and Environmental Influences on the Stability of Withdrawn Behaviour in Children: a Longitudinal, Multi- Informant Twin Study

This study examined the contribution of genetic and environmental influences on the stability of withdrawn behaviour in childhood using a longitudinal multiple rater twin design. Maternal and paternal ratings on the withdrawn subscale of the Child Behavior Checklist were obtained from 4889 families when the twins were 3, 7, 0 and 2 years old. Withdrawn behaviour showed considerable stability throughout childhood, with correlation coefficients ranging from about .30 for the 9-year time interval to .65 for shorter time intervals. Individual differences in withdrawn behaviour were found to be largely influenced by genetic effects at all four time points, in both boys (50-66%) and girls (40-6%). Shared environmental influences explained a small to modest proportion (2 – 23%) of the variance at all ages and were slightly more pronounced in girls. Nonshared environmental influences were of moderate importance to the variance at all ages in both boys (2-38%) and girls (24-4%).The stability of withdrawn behaviour was largely explained by genetic effects, accounting for 74% of stability in boys and 65% in girls. Shared environmental effects explained 8% (boys) and 8% (girls) of the behavioural stability. As the main part of the shared environmental influences on stability was common to both raters, these effects could not be due to rater bias. Nonshared environmental effects accounted for the remaining covariance over time. Genetic and shared environmental correlations across age of the reliable phenotype approached unity, indicating that the same genes and shared environment influence withdrawn behaviour throughout childhood.