Parental characteristics and offspring internalizing behaviors : understanding the associations using quantitative genetics

Sammanfattning: Internalizing problems increase dramatically from childhood to adolescence and account for a large proportion of mental health problems worldwide. During the past decade research has documented a robust association between offspring internalizing problems and different aspects of parental characteristics, such as parenting practices and psychiatric disorders. Findings from twin and family studies have suggested that this association is influenced by both genetic and environmental factors. Nevertheless, prior studies have had limited possibilities to disentangle familial confounding from causal environmental mechanisms. Therefore, we aimed to use different genetically informative designs to explore the direction and etiology of the association between different parental characteristics and offspring internalizing behaviors. In Paper I, we examined a sample of Swedish twins to understand the direction and etiology of the association between different parenting styles and offspring internalizing behavior from adolescence to early adulthood. We found that daughters internalizing behavior influenced an emotional overinvolved behavior from their parents. Twin analyses indicated that this association was mediated by genetic factors. In Paper II, we investigated the impact of offspring death and suicide on psychiatric disorders among their parents in a cohort defined by nationwide registers. Parents exposed to offspring suicide had considerably higher risk for subsequent psychiatric hospitalization. Furthermore, a shared genetic liability for psychiatric disorder seemed important judging from family-based analyses. In Paper III, we specifically examined the suicide risk among offspring of parents hospitalized for schizophrenia and the mechanisms behind this association. We observed a doubled risk of suicidal behavior in offspring. Cousin comparisons suggested that environmental factors play an important role in this association. In Paper IV, we explored if ADHD and suicidal behavior shared genetic and environmental factors. We found an increased risk of both completed and attempted suicide among relatives of individuals with ADHD. The pattern of familial aggregation indicated genetic influences for this association. In conclusion, genetic and environmental factors contributed to the associations between parental characteristics and offspring internalizing behavior. Internalizing behaviors in offspring predicted both parenting and psychiatric disorders through genetic mechanisms. However, we could also show that specific parental psychiatric disorders predicted offspring internalizing behaviors through environmental mechanisms. In addition, we found that genetic factors for internalizing behavior to some extent is shared with genetic factors for ADHD. Future research using other genetically informative designs to control for familial confounding is necessary to provide a clearer understanding of the etiological link between parental characteristics and offspring internalizing behavior.