Risk factors for schizophrenia and affective disorders in the Northern Finland Birth Cohort studies

Schizophrenia and psychotic and nonpsychotic affective disorders are a major public health problem, affecting over 10% of the population. Risk factors for these disorders are for instance genetic factors, complications of pregnancy and childbirth, substance use, poor school success, life events, somatic illness, and socioeconomic factors. Many of these potential risk factors may be pluripotent, resulting in risk for diverse mental health outcomes. It is also likely that risk factors differ between psychotic and nonpsychotic affective disorders, but research on this is quite scarce. The research project aims to study extensively biological and environmental risk factors, their specificity, and interactions and causal pathways in schizophrenia, psychotic and nonpsychotic affective disorders in two large birth cohorts. Regarding interactions of risk factors, we study especially mechanisms, how genetic risk (estimated with polygenic risk scores) associate with early life risk factors or substance use in onset of these disorders. A survey related to the effects of the COVID-19 pandemic will be used to study if earlier vulnerability affects the risk of increased depressive symptoms as a consequence of the pandemic.

The study is based on the Northern Finland Birth Cohorts 1966 (n = 11647) and 1986 (n = 9340), which are two population-based studies where data on individuals have been collected progressively since pregnancy. There are currently 1,345 (11.9%) people in the 1966 birth cohort and 1,168 (12.5%) people in the 1986 birth cohort with schizophrenia or affective disorder. In addition to traditional epidemiological methods, structural equation modeling and machine learning methods are used to analyze data. In sensitivity analyses, we can replicate analyses using depressive symptoms instead of diagnoses.

The innovative methodological approaches hold promise for scientifically and clinically significant findings. Some of the potential risk factors are modifiable, finding these may renew the knowledge on aetiology of schizophrenia and affective disorders. These birth cohorts offer a unique opportunity to study the interactions of risk factors and possible pragmatic causal pathways to disease onset in two unique datasets. Research findings can be used to more effectively design interventions to reduce and alleviate these serious and critical illnesses with public health impact.