Psychotic-Like Experiences in Adolescence Occurring in Combination or Isolation: Associations with Schizophrenia Risk Factors.

OBJECTIVES: Individual adolescent psychotic-like experiences (PLEs) are associated with schizophrenia risk factors. As DSM-5 schizophrenia requires the co-occurrence of at least two psychotic symptoms, we investigated whether co-occurring adolescent PLEs have stronger associations with schizophrenia risk factors, lower quality of life and functioning, and have higher heritability, than individual PLEs. METHODS: Participants were 9646 16-year-old twins from the longitudinal Twins Early Development Study. We investigated co-occurrence of high questionnaire scores for three PLE combinations: (1) paranoia and hallucinations; (2) paranoia or hallucinations, and cognitive disorganization; and (3) paranoia or hallucinations, and negative symptoms, and their associations with 11 schizophrenia-relevant variables by regression analysis and structural equation twin modeling. RESULTS: Against expectation, none of the co-occurring PLEs had the nominally strongest associations significantly more often than individual PLEs. Co-occurring PLEs had the strongest associations with bullying victimization, cannabis use and lower life satisfaction, but individual PLEs had the strongest associations with cognitive function variables. Obstetric complications were most associated with negative symptoms. Secondary analysis revealed that co-occurrence of cognitive disorganization and negative symptoms had the nominally strongest associations with most schizophrenia-relevant variables overall and relatively high heritability (67%). CONCLUSIONS: Focusing on co-occurrence enhances some individual PLE associations but obscures others. The combination of subjective cognitive disorganization plus observed negative symptoms showed a broad range of enhanced associations with schizophrenia-relevant variables. Future research could investigate associations with other risk factors and the ability of this PLE combination to predict onset of schizophrenia.