Causes, consequences, and life-course trajectories of personality pathology - a longitudinal extended children-of-twins study

Personality disorders affect the way a person thinks, feels, and behaves, and can be destructive in many areas of life. This can manifest as extreme distrust and paranoia, intense mood swings, impulsive behavior with little regard for the safety or well-being of others, or crippling perfectionism and social inhibition. Personality disorders often place a heavy burden not only on the affected individual but also on those close to them, particularly partners and children. Despite the fact that around 10% of the population meets the criteria for personality disorders, we have less knowledge about the causes, life course, and psychosocial consequences of these disorders compared to other mental disorders. So far in this project, we have analyzed register data to examine the relationship between parental personality pathology and psychosocial outcomes in children’s, such as education and school performance. In the next phase, we will invite all Norwegian twins born between 1967 and 1979 to participate in a new data collection. Some of these twins have already taken part in previous studies on personality disorders in 1999 and 2010, but we will now also include their siblings, partners, and children over the age of 16. This will enable us to track the development of personality disorders and other mental illnesses from when the participants were young adults over a period of 25 years. By linking these data with information from public registers, we can analyze how these disorders affect different areas of life, such as physical health, education, and workforce participation, over time. The unique aspect of this project is that by including twins, partners, and children, we can study how personality disorders run in families, explore the influence of the upbringing environment, and at the same time account for the impact of genetic factors.

Individuals with personality pathology are at high risk of suffering, disability, and a range of negative health and psychosocial outcomes. Since personality pathology can have a detrimental impact on virtually all social interactions, the risk of distress and negative outcomes also extends to people in close relationships with those afflicted, in particular their spouse and children. In the proposed study we aim to assess personality pathology and clinical disorders in all twins born 1967-1979, as well as their non-twin siblings, spouses, and children over 16 years of age. To this stem we will link data on a subset of the same cohort, from the only large and genetically informative population representative study assessing all PDs in DSM-IV (AI/AII study) , the 10 year follow-up (AI/AII-FU), as well as data from national health and social registries unique to the Scandinavian countries. This will permit us to advance the international research front with respect to personality pathology on three key areas. First, we will investigate the etiology of personality pathology across a 25 year span from early to middle adulthood, as well as the causes underlying their longitudinal relationships with clinical disorders. Second, we will determine the cumulative health, functional and psychosocial outcomes of personality pathology. Third, we will provide unique insight into the processes by which personality pathology and clinical disorders are transmitted across generations, and the impact and mechanisms by which children are influenced by personality pathology in parents, and visa versa. The children-of-twins-design will permit us to accurately estimate the genetic influence on PP, investigate the causal effects of parental mental health problems on children, and determine the risk or protective effects of a range of measured environmental exposures, all while controlling for genetic confounding and circumventing the limitations inherent in the classical twin design.