Environmental risk factors and antecedents for schizophrenia: A focus on social stressors

Abstract

Background Identifying at-risk individuals during the premorbid stage of the illness pathway to schizophrenia relies on accurate identification of the risk factors and antecedents that precede the onset of psychosis. Progress has been made in identifying people during the prodromal stage; however, identifying children and adolescents prior to this stage may be the key to preventing psychosis. The aims of this thesis were to assess the evidence on non-genetic environmental risk factors and antecedents of schizophrenia, with a focus on social stressors. Childhood maltreatment and social-emotional functioning were investigated in adults with schizophrenia and in putatively at-risk children. Method The thesis incorporated systematic meta-review, meta-analysis, and primary data analysis methods. A meta-review presented and quality assessed evidence on risk factors and antecedents of schizophrenia from reviews with pooled data. Meta-analyses assessed relationships between childhood maltreatment and schizophrenia, and between childhood social withdrawal and schizophrenia compared with symptoms of social withdrawal in 9-14 year old children at-risk for schizophrenia. A data-linkage study assessed relationships between childhood maltreatment and social-emotional functioning in five year-old children with and without parental schizophrenia. Results Physical risk factors included advanced paternal age, obstetric complications, infectious agents, and cannabis use. Social risk factors included urbanicity, migration, ethnicity, and socio-economic status, with social stress underlying all of these factors. Antecedents included motor dysfunction and low intelligence quotient. Meta-analysis identified a three-fold increased risk of childhood adversity in schizophrenia. Meta-analysis identified large effects of social withdrawal in 9-14 year-old children who later developed schizophrenia and in similarly-aged children displaying a triad of antecedents of schizophrenia, with smaller effects in similarly-aged children with a family history of schizophrenia. The data-linkage study found associations between all types of maltreatment and poor social-emotional functioning that were greater in magnitude among children with no parental history of schizophrenia than in children with parental schizophrenia. Conclusions The pathways to schizophrenia are complex, involving multiple risk factors and antecedents that add to, mediate, or moderate each other’s effects. This thesis provides new information regarding potential risk factors and antecedents that might be used to identify at-risk children putatively in the premorbid stage of schizophrenia.