Childhood signs of ADHD and psychosocial outcomes in adolescence : a longitudinal study of boys and girls

Sammanfattning: Childhood neurodevelopmental problems (NDPs; encompassing attention deficit hyperactivity disorder [ADHD], autism spectrum disorder [ASD], tic disorder [TD], learning disorder [LD], and developmental coordination disorder [DCD]), affect around 10% of children worldwide. ADHD is the most common disorder, with an estimated prevalence between 5 and 10%. Based on its relatively high prevalence and associated impairments and adverse outcomes, ADHD is considered a major public health problem. The etiology of ADHD is multifactorial, including both genetic and environmental factors. ADHD affects both boys and girls in various areas of functioning; including academic, cognitive, psychosocial, and mental health. Previous longitudinal research on ADHD has rarely included aspects of comorbidity in relation to such outcomes. Also, it remains unclear how genetic and environmental factors influence the association between ADHD and internalizing problems during childhood and adolescence. To avoid the potentially artificial demarcation of a diagnostic cut-off, several studies have assessed the degree of core ADHD-symptoms rather than the clinical diagnosis. Such work indicates that subthreshold levels of ADHD may also be associated with negative outcomes such as poorer academic achievements, lower selfesteem, and relationship problems. A particular challenge for society lies in the fact that only children who are clinically assessed and diagnosed with ADHD may be entitled to care and support, when in fact individuals with subthreshold level symptoms might also benefit from such interventions. The general aim of this thesis was to investigate how childhood symptoms of ADHD affect psychosocial outcomes in adolescence, with a special focus on gender differences. We used data from a population-based cohort of twins, who were assessed for the presence of NDP symptoms during childhood and followed up at age 15. Study I investigated the diagnostic predictive validity of the screening-interview A-TAC, an instrument that is used throughout all studies in this thesis. The results demonstrated that ATAC is an effective screening tool for NDPs, and that it can be used for the purpose of predictive assessment in the general population. Overall, A-TAC demonstrated satisfactory psychometric properties as a screening instrument. Study II examined the association between childhood signs of ADHD and/or other NDPs (at age 9 or 12) and psychosocial outcomes at age 15. The results demonstrated that symptoms of NDPs or other mental health problems at the age of 9 or 12 were associated with a higher degree of psychosocial problems during adolescence. Despite the presence of comorbidity, childhood ADHD symptoms stood out as the most important risk factor for later antisocial development and impaired daily functioning. Study III examined if different levels of ADHD symptoms were differentially associated with psychosocial problems in adolescent boys and girls. ADHD symptoms as well as their associated negative outcomes were dimensionally distributed in the study cohort. Girls and boys displayed somewhat different risk profiles, even after controlling for other neuropsychiatric symptoms. Study IV explored the relative contribution of genetic and environmental influences associated with childhood ADHD and internalizing problems to symptoms of internalizing problems during adolescence. ADHD and internalizing problems were associated. There was a gender difference in the genetic explanation of internalizing problems at age 15. In both boys and girls, both new genetic and new environmental factors emerged in adolescence. In summary, childhood symptoms of ADHD turned out to be the most important risk factor for adolescent antisocial behavior and impaired daily functioning, despite the presence of comorbid symptoms. During adolescence, increasing levels of ADHD-related symptoms were associated with increasing levels of psychosocial problems. Girls and boys displayed somewhat different risk profiles, e.g. girls displayed more internalizing symptoms and seemed to have a higher risk for drug misuse. The finding that ADHD symptoms were associated with higher drug misuse in girls motivates particular attention and active screening routines. The findings also point to the need for increased awareness and further study of the complex etiologic and developmental relationship between internalizing symptoms and ADHD.