Behavior problems in 5-year-old monozygotic and dizygotic twins: Genetic and environmental influences, patterns of regulation, and internalization of control

Genetic influence on externalizing problems, internalizing problems, and attentional/activity problems in 5-year-olds was consistently identified across informants and assessment contexts. Effects of the shared environment were identified as well but with less consistency (i.e., only from parents, not teachers, and more from father than mother reports). Correlations between observed patterns of regulation at ages 3, 4, and 5 years and behavior problems at age 5 years were often significant, but low in magnitude and specific to teacher reports. Adaptive internalization of control at each age (e.g., frustration tolerance, capacity to attend and focus, good impulse control) predicted fewer externalizing problems. Internalization of standards, reflected in children's moral themes, understanding of reciprocity, and constructive social problem solving, also were sometimes associated with fewer problems. Significant correlations were low in magnitude and again specific to teacher reports. Externalizing problems were more prevalent for boys than girls, and regulation (i.e., internalization of control and standards) was more characteristic of girls than boys.