A Genetic Study of Problem Behaviors in Children

Behavioral/emotional problems are common among children of preschool and school age. Verhulst, and Koot (1992, p. 130) reviewed prevalence studies published since 1965. They reported a median prevalence rate for general psychiatric dysfunction in children and adolescents of l3%. This number illustrates that problem behaviors in children present a public health problem that cannot be ignored. During the 1960s and 1970s, many people came to dismiss the role of genetic factors in behavioral/emotional problems in children, and to emphasize the power of environmental influences (Rutter, 1991). However, recent years have shown an increased interest in the study of genetic factors (Piomin, in press; Rutter et al., 1990a). This has led to a broader recognition that genetic as well as environmental factors may be involved in children's problem behaviors. Compared to the number of studies concerning the genetic influence in adult psychiatric disorders, only few have focussed on the role of genetic factors in child psychiatric conditions. A number of family, adoption, and twin studies have demonstrated the probable importance of genetic factors in relatively well-delineated child psychiatric conditions such as autism (Folstein, & Rutter, 1977), enuresis (Bakwin, 1971), tics (Pauls, Cohen, Heimbuch, Detlor, & Kidd, 1981), anorexia nervosa (Holland, Hall, Murray, Russel, & Crisp, 1984), and stuttering (Vandenberg, Singer, & Pauls, 1986). Other studies have investigated the genetic and environmental contributions to the commoner varieties of children's problem behaviors such as depression (Wierzbicki, 1987), hyperactivity (Goodman, & Stevenson, 1989a,b), delinquency (Rowe, 1983), and aggression (Ghodsian-Carpey, & Baker, 1987; Plomin, Foch, & Rowe,- 1981). Nevertheless, for the vast majority of problem behaviors we cannot yet say whether genetic influence is significant, let alone estimate its magnitude (Plomin, in press). The primary aim of this study was to address the most basic question of the extent of genetic involvement in the commoner varieties of problem behaviors in children. Estimates of genetic influences can be obtained by disentangling genetic and environmental influences. The genetic study in this dissertation is therefore as informative about environmental influences as it is about genetic influences. The value of a genetically informative design to study environmental influences is further illustrated by the possibility to assess the relative importance of two kinds of environmental influences. Environmental influences can be distinguished according to whether they have an impact on all children growing up in the same family, or uniquely influence one specific child. Parental rearing practices, illness/loss of a parent, or the socio-economic status are examples of possible shared environmental influences. Accidents, differential parental treatment, or peer group influences are examples of non-shared environmental influences because these are likely to affect the behavior of only the child of concern. Disentangling genetic, shared environmental, and non-shared environmental influences may be scientifically and clinically useful. For instance, for most psychological characteristics in the area of personality, psychopathology, and cognition, the relevant environmental influences are not shared by children in the same family (Plomin, & Daniels, 1987). A possible implication is that research efforts and clinical interventions might perhaps better focus on environmental variables that affect just one child, than on environmental variables that are assumed to affect all the children in the family. An important part of this dissertation concerned problem behaviors in preschool children. Little is known about genetic influences on problem behaviors in preschool children, and the present study is one of the first reports on this subject. Further, a number of studies reported a substantial stability of problem behaviors in children (Richman, Stevenson, & Graham, 1982; Verhulst, & Van Der Ende, 1992a,b). Since early adjusttnent is an important predictor of the level of problem behavior at a later point in time, this argues for a greater understanding of the determinants of problem behaviors in young children. An increased knowledge might help to optimalize clinical interventions, and prevent later maladjustment