Personality traits, risk factors and comorbidities in Attention-deficit/hyperactivity disorder

Background: Attention-deficit/hyperactivity disorder (ADHD) comprises cognitive and behavioural traits present from childhood. During lifespan, people with ADHD are more prone to develop psychiatric- and somatic comorbidities compared to those without ADHD. Knowledge about possible risk factors, personality traits and comorbidities may increase the understanding of underlying mechanisms for ADHD. Aims: The main aim of this thesis was therefore to explore clinical features and potential causal factors in ADHD: 1) Explore personality traits and their relationship to psychiatric comorbidities in adults with ADHD; 2) Investigate maternal inflammatory and immune system diseases as prenatal risk factors for offspring ADHD; 3) Explore possible sex-specific associations between ADHD and autoimmune diseases; 4) Describe the current knowledge on somatic comorbidity in adult ADHD. Materials and methods: 1) Personality traits were assessed by a self-report questionnaire and psychiatric comorbidity by an interview in a group of persons with adult ADHD and a comparison group; 2) and 3) Prenatal risk factors and comorbidity were assessed by linking data from Norwegian population-based registries such as the Medical Birth Registry and the Norwegian Prescription Database; 4) Knowledge on adult ADHD and somatic comorbidity was described in a systematic literature review. Results: 1) The personality dimensions Novelty Seeking and Harm Avoidance were highly associated with ADHD. However, these associations were dependent on common life-time psychiatric comorbidities in ADHD; 2) Maternal multiple sclerosis, rheumatoid arthritis, diabetes mellitus type 1, asthma and hypothyroidism significantly increased the risk of offspring ADHD; 3) ADHD was associated with psoriasis in both sexes, and with Crohn`s disease and ulcerative colitis in females; 4) Obesity, sleep disorders and asthma were well-documented comorbidities in adult ADHD. Conclusions and consequences: Our findings add to the evidence that ADHD has many facets. Associations with immune-related diseases both as prenatal risk factors and somatic comorbidities may inform further aetiological research. Clinicians need to acknowledge personality traits and comorbidities in order to provide individuals with ADHD the best understanding and treatment