Background: Attention deficit/hyperactivity disorder (AD/HD) and autism spectrum disorders (ASDs) are early-onset, but often life-time impairing, neurodevelopmental disorders. They are highly overlapping and seem to carry considerable risks of negative outcomes, psychiatrically and psychosocially. Childhood hyperactivity is a known risk factor for early-onset conduct disorder (CD), but details concerning the associations between neurodevelopmental problems, aggression, and antisocial personality disorder (ASPD) in adult age are still uncertain. The current diagnostic subdivision of the ASDs is based on children, while the adult characteristics, including patterns of comorbidity and psychosocial adversities, have been less studied, especially in subjects without concomitant intellectual disability. Objectives: The overall aim of this thesis was to describe the adult outcome of AD/HD and ASDs. Specific aims were to: (1) review prospective, longitudinal studies of the adult outcome of childhood hyperactivity, equivalent to AD/HD, with special regard to ASPD, (2) investigate the relationships between AD/HD, ASDs, and different types of aggressive behaviours, (3) describe the clinical presentation, including personality development and psychosocial outcome, in normal-intelligence adult subjects with ASDs. Method: The first paper is a systematic meta-analysis of published studies. The subsequent studies are descriptive analyses of common clinical assessment protocols from consecutive groups of adults either referred for clinical evaluations of childhood-onset neuropsychiatric disorders, for forensic psychiatric investigations, or recruited to a population-based, longitudinal study of teenage-onset anorexia nervosa (AN). Results: Childhood hyperactivity increases the risk for CD, which is found in at least one-third of all hyperactive children, forming the starting point for the development of aggressive antisociality in adulthood in about half of cases with the combination of hyperactivity and CD in childhood. Support for the hypothesis that childhood hyperactivity, in the absence of early CD, carries a risk for adult ASPD, is still lacking (Paper I). Both conditions are, however, predictors of aggression in adults, together with substance-related disorders and poor development of the character trait Cooperativeness. ASD traits or symptoms did not generally predict aggression but may be associated with unique violent offences (Paper II). Among subjects with normal-intelligence ASDs, life-time psychiatric comorbidity was very high, and measures of outcome indicated low psychosocial functioning. AD/HD was common in all ASD subject categories studied with the notable exception of subjects with AN, none of whom had AD/HD. ASPD and substance-related disorders were more common in patients with an atypical ASD as compared to Asperger´s disorder or autistic disorder. Among all adults diagnosed with an ASD, less than half led an independent life and comparatively few had ever had a long-term relationship. Female subjects more often reported having been bullied at school than male subjects (Paper III and IV). Discussion and conclusions: Childhood-onset neuropsychiatric conditions such as AD/HD and ASDs are relevant for adult psychiatric phenotypes but insufficiently studied. Current classifications suffer from the hiatus between child- and adolescent psychiatry and adult psychiatry and future diagnostic concepts ought to be longitudinal with a life-time perspective on cognitive and emotional development and a patient-centred focus rather than fragmented into complex patterns of “comorbidities”
