On Psychotic Phenomena and Unruliness: studies on the childhood risk for severe mental illness

Psychiatric disorders in adulthood, including severe mental illnesses, commonly have antecedents in childhood or adolescence. A better understanding of the developmental pathways of psychiatric problems in early childhood might help to achieve a more comprehensive understanding of severe mental illness in adults. The general aim of this thesis was to gain insights into the neurodevelopmental pathways of children at increased risk for severe mental illness. Here we focussed on two prevalent yet impairing psychiatric phenotypes of childhood: psychotic phenomena and disruptive behaviour problems. Each of these constellations of psychiatric symptoms is in its own right predictive of substantially poorer psychosocial functioning in the long term. All studies described in this thesis were conducted in the context of the Generation R Study, a population-based cohort study in Rotterdam, the Netherlands. The findings and interpretations of the individual studies are discussed in the broader context of the existing literature. More specifically, several methodological considerations are discussed pertaining to the neurodevelopmental model of psychosis, the neurodevelopmental model of disruptive behaviour, analytical methods of behavioural heterogeneity, assessment of psychotic experiences in children and the link between cannabis use and psychopathology. We conclude with several recommendations for improved clinical practice and future research