Abstract
Background. Evidence suggests that in affective, non-psychotic
disorders: (i) environmental exposures increase risk of subthreshold
psychotic experiences (PEs) and strengthen connectivity between domains
of affective and subthreshold psychotic psychopathology; and (ii) PEs
are a marker of illness severity.
Method. In 3021 adolescents from the Early Developmental Stages of
Psychopathology cohort, we tested whether the association between PEs
and presence of DSM-IV mood disorder (MD)/obsessive-compulsive disorder
(OCD) would be moderated by risk factors for psychosis (cannabis use,
childhood trauma and urbanicity), using the interaction contrast ratio
(ICR) method. Furthermore, we analysed whether the interaction between
environment and PEs was mediated by non-psychotic psychopathology.
Results. The association between PEs and MD/OCD was moderated by
urbanicity (ICR = 2.46, p = 0.005), cannabis use (ICR = 3.76, p = 0.010)
and, suggestively, trauma (ICR = 1.91, p = 0.063). Exposure to more than
one environmental risk factor increased the likelihood of co-expression
of PEs in a dose-response fashion. Moderating effects of environmental
exposures were largely mediated by the severity of general non-psychotic
psychopathology (percentage explained 56-68%, all p < 0.001). Within
individuals with MD/OCD, the association between PEs and help-seeking
behaviour, as an index of severity, was moderated by trauma (ICR = 1.87,
p = 0.009) and urbanicity (ICR = 1.48, p = 0.005), but not by cannabis
use.
Conclusions. In non-psychotic disorder, environmental factors increase
the likelihood of psychosis admixture and help-seeking behaviour through
an increase in general psychopathology. The findings are compatible with
a relational model of psychopathology in which more severe clinical
states are the result of environment-induced disturbances spreading
through a psychopathology network.
