People who suffer from personality disorders have ways of thinking, emotional reactions, or behavior, that has a destructive impact on many areas of their lives. This can manifest as extreme mistrust and paranoia, violent fluctuations in emotions, impulsive behavior without consideration for the well-being or security of others, or paralyzing perfectionism and inhibition in social situations. Personality disorders can be devastating for the person afflicted, but also for others in close relationships, especially their partners and children. Although about 10% of the population meets the criteria for personality disorders, we have less knowledge about their causes, life course development, and psychosocial consequences, than we have for other mental disorders.
In this project, we will carry out a data collection on all Norwegian twins born between 1967 and 1979. Some of these twins have participated in data collections on personality disorders in 1999 and 2010, but now we will also invite their other siblings, partners, and children over 16 years of age. This will enable us to follow the development of personality disorders and other mental disorders, from the participants are young adults, and over a period of 25 years. By linking to information from public registers, we will be able to study the long-term consequences of personality disorders on domains such as physical health, education, and work participation. Most uniquely, linking data from twins, partners and children will allow us to study how personality disorders are transmitted within families, and test possible environmental causes, while we can assess and take into account the influence of genes.
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.