Adolescent adjustment problems : the role of heritability and family environment

Abstract

Approximately one fifth of children and adolescents in Europe and United States of America suffer from behavioral, emotional or developmental problems. More effective prevention and intervention of these problems may be achieved through understanding the role of genetic and environmental factors. This thesis investigates the interplay between genes and environments in the development of adolescent adjustment problems, with a focus on the role of parental practices.

The studies included in this thesis are based on data from two studies: Twin study of Child and Adolescent Development (TCHAD) and Twin and Offspring Study in Sweden (TOSS). TCHAD is an ongoing Swedish longitudinal population-based study of 1,480 twin pairs concerning health and behavior in children and adolescents. The twins and their parents have been contacted on four different occasions (8-9 years, 13-14 years, 16-17 years, and 19-20 years) with good to excellent response rates. TOSS is a two-cohort study of 909 pairs of twins, their spouse or partner, and one biological adolescent child. TOSS aims to better understand the relationships within the family and how they are associated with the mental health of the family members.

The data was analyzed using conventional and newly developed twin methods. Results of Paper IV revealed that antisocial behavior that persists from late childhood to early adulthood is to a major part influenced by familial factors in both males and females. One of the well-investigated environmental familial risk factors for antisocial behavior is parenting practices. Research suggests that parenting is partly explained by genetic effects emanating from child, which is usually interpreted as an indication of evocative genotypeenvironment correlation (rGE). Paper I shows that the genetic contributions to the association between parental criticism and antisocial behavior in adolescents can be explained by heritable early adolescent aggression. These findings are consistent with evocative rGE.

The main focus of Paper II is an extension of the existing children-of-twins model (ECOT), enabling to test for different types of rGE. The ECOT was applied to examine the nature of rGE in the association between maternal emotional overinvolvement and internalizing behavior problems in adolescents. The results suggest that evocative rGE is important for this association. That is, mothers tend to get more emotionally overinvolved in their parenting as a response to internalizing behavior problems in their children. Similarly, mothers critical behavior seems to be evoked by externalizing behavior in adolescents, as suggested by Paper III, whereas fathers criticism was found to influence the development of externalizing problems in an environmental way, that is, a way independent of either fathers or adolescents heritable characteristics.

Future research should focus on studying the association between adverse parenting and adjustment problems across the development, from childhood to adulthood. In such studies, different types of mechanisms rGE, genotype-environment interaction, and direct environmental influences are possible to be examined simultaneously. As a result, more details about when and how behavior problems start and develop could be gained, hopefully helping to identify effective prevention and intervention targets.