Letter to the Editor: Beyond childhood trauma – stressful events early and later in life in relation to psychotic experiences

Traumatic experiences during childhood increase the risk for psychopathology later in life (Danese & Baldwin, 2016), yet the underlying mechanisms remain elusive. In the context of psychotic disorders, Reininghaus et al. (2016) recently found support for the notion that enhanced sensitivity and increased threat anticipation to stress are important psychological mechanisms in the pathways from childhood trauma to psychosis (as put forward by Morgan & Hutchinson, 2010). The question is whether these mechanisms are relevant to the development of psychotic symptoms with a need for care, or merely contribute to a more general vulnerability for psychotic experiences, including those without a need for care. This can be studied by comparing patients with a psychotic disorder to individuals with frequent non-clinical psychotic experiences. We previously found that both groups reported equally high rates of childhood trauma (Daalman et al. 2012), suggesting that traumatic experiences early in life make a person vulnerable for psychotic experiences in general rather than forming a specific risk factor for a full-blown psychotic disorder. Notably, only a minority of maltreated children eventually develop psychotic experiences, whether or not part of a psychotic disorder, whereas others do not develop such experiences. To understand these differences, we need to gain more insight into the mechanisms involved in the pathways from childhood trauma to clinical and non-clinical psychotic experiences in adulthood. During the past years, interest has increased regarding the role of stressful events after childhood in the development of psychotic experiences or a psychotic disorder. In individuals who have experienced maltreatment as a child, the risk for trauma exposure later in life is elevated (Acierno et al. 1999; Kim et al. 2014), which could be viewed as a second hit. According to meta-analytic data, exposure to adult stressful life events is associated with a higher risk of subsequent onset of a psychotic disorder or psychotic experiences, compared with controls [odds ratio (OR) 3.19, 95% confidence interval (CI) 2.15–4.75] (Beards et al. 2013). However, none of the included studies adjusted for childhood trauma (Beards et al. 2013), while the impact of stressful events on psychotic experiences later in life may be greater in individuals with a history of maltreatment. For instance, Read et al. (2003) found that a combination of both child and adult abuse, rather than either one alone, best predicted psychotic symptoms in psychiatric patients. In a population-based study by Morgan et al. (2014), early abuse and life events combined synergistically to increase the odds of subclinical psychotic experiences. In a population-based 10-year prospective study, only the highest levels of exposure to adversity (510 recent events) was related to psychotic symptoms, and this relationship was stronger in individuals who were maltreated during childhood (Lataster et al. 2012). Until recently, studies rarely considered the subjective interpretation of life events (Beards et al. 2013). However, as Reininghaus et al. (2016) demonstrated, psychological and cognitive mechanisms are important when evaluating the effects of childhood trauma and stressful events later in life. Indeed, when childhood trauma and adult trauma are related to both psychotic experiences as well as psychotic disorders, the question remains why some individuals pass the psychosis threshold while others do not. By studying patients with a psychotic disorder, individuals with frequent non-clinical psychotic experiences and controls without psychotic experiences, we aimed to investigate: