Psychopathic personality in adolescence : Genetic and environmental influences

Psychopathy, or psychopathic personality, is a personality disorder characterized by a constellation of deviant interpersonal, affective, and behavioral dimensions. It has consistently been shown that the psychopathic personality can be used to understand the development of antisocial behavior in adolescents. Less research has been devoted to exploring the underlying etiology of psychopathic personality. There has also been a lack of genetically sensitive longitudinal studies that have examined the developmental associations between psychopathic personality and putative psychopathological correlates. This thesis has used longitudinal and multivariate twin data to clarify both the etiology of psychopathic personality and its association with other psychopathological problems. The data used in this thesis comes from the Twin Study of Child and Adolescent Development, a prospective longitudinal study with data collected when the twins were 8-9, 13-14, 16-17, and 19-20 years old. Study I in this thesis showed that genetic factors contributed substantially to the stability of the higher-order psychopathic personality factor, whereas environmental factors were of little importance. We also found specific genetic stability in the Callous/unemotional (affective) and Impulsive/irresponsible (behavioral) dimensions. Study II showed that persistent externalizing problems in childhood was associated with both psychopathic personality and antisocial behavior in adolescence. Twin analyses showed that genetic factors explained the association between persistent externalizing problems and psychopathic personality, whereas shared environmental factors explained the association between persistent externalizing problems and antisocial behavior. In Study III it was shown that that psychopathic personality in adolescence predicted antisocial behavior in adulthood via genetic effects, but not the other way around. However, bidirectional effects were found when a measure of persistent antisocial behavior was used. In Study IV, the higher-order psychopathic personality factor was associated with externalizing problems due to genetic factors, whereas the specific variances in the Callous/unemotional and Impulsive/irresponsible dimensions were divergently related to psychopathological problems. Findings in this thesis highlights the importance of both general and specific etiologic factors in understanding the stability and change of psychopathic personality, as well as for identification of risk and protective factors in the development of externalizing and internalizing problems. Future attempts to identify specific genes could therefore focus on the general, but also the specific variance of the psychopathic personality constellation. Second, this thesis has added to previous research by showing that adolescent psychopathic predicts adult antisocial behavior via genetic effects, but also that persistent antisocial behavior predicts adult psychopathic personality. Researchers are encouraged to include measures of psychopathic personality in younger samples and at several assessment points to clarify the nature of the association between psychopathic personality and antisocial behavior in more detail