Examining the continuum of psychosis: Frequency and characteristics of psychotic-like symptoms in relatives and non-relatives of patients with schizophrenia.

BACKGROUND: A key finding underlying the continuum of psychosis concept is the presence of psychotic-like experiences (PLEs) in healthy subjects. However, it remains uncertain to what extent these experiences are related to the genetic risk for schizophrenia and how far they actually resemble attenuated forms of psychotic symptoms. METHODS: Forty-nine adults with no history of mental illness in first-degree relatives and 59 siblings of patients with schizophrenia were rated on the psychosis section of the Computerized Diagnostic Interview Schedule IV (C DIS-IV) and the Rust Inventory of Schizotypal Cognitions (RISC). Those who rated positive on the CDIS-IV were re-interviewed using the lifetime version of the Present State Examination 9th edition (PSE-9) and the Structured interview for Schizotypy (SIS). RESULTS: Seventeen (34.69%) of the non-relatives and 22 (37.29%) of the relatives responded positively to one or more of the psychosis questions on the DIS. This difference was not significant. RISC scores were also similar between the groups. At follow-up interview with the PSE-9, 13/40 PLEs (32.50%) in the non-relatives were classified as possible or probable psychotic symptoms compared to 11/46 (23.91%) in the relatives. Using liberal symptom thresholds, 5 of those who attended the follow-up interview (2 non-relatives and 3 relatives) met SIS criteria for schizotypal personality disorder. CONCLUSIONS: Rates of PLEs, however considered, do not differ substantially between relatives and non-relatives of patients with schizophrenia. Only a minority of PLEs picked up by screening interviews resemble attenuated forms of psychotic symptoms.