Guest Lecture on the Origins of Psychosis

Abstract

It has commonly been assumed that the psychotic disorders (conditions that involve hallucinations and delusions, and which usually lead to diagnoses such as ‘schizophrenia’ or ‘bipolar disorder’) are largely genetic in origin. This assumption is usually justified by referring to heritability estimates that exceed 80%. However, these estimates are not measures of causation and their misinterpretation is an example of one of the most common mistakes in statistics – assuming that correlation proves causality. In fact, major environmental influences are possible even if heritability approaches 100%. The only way of assessing these influences is to look for them. In recent years, considerable evidence had accumulated on a range of environmental risk factors for psychosis, including urban environments, poverty, migration and trauma. In each of these cases, the effects are particularly strong when these exposures occur in childhood.

The guest lecture will focus particularly on the effects of childhood trauma which, in a meta-analysis, raises the risk of adult psychosis by a factor of 3. In three epidemiological datasets, specific patterns of association were found, with childhood sexual abuse being a particular risk factor for hallucinations and disruption of attachment bonds a particular risk factor for paranoid beliefs. These findings point to psychological mechanisms that explain these associations: dissociative states in the case of hallucinations and insecure attachment styles in the case of paranoia. Implications for the treatment and prevention of severe mental illness will be discussed.