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Diagnostic categories do not completely reflect the heterogeneous expression of psychosis. Using data from the EU-GEI study, we evaluated the impact of schizophrenia polygenic risk score (SZ-PRS) and patterns of cannabis use on the transdiagnostic expression of psychosis. We analysed first-episode psychosis patients (FEP) and controls, generating transdiagnostic dimensions of psychotic symptoms and experiences using item response bi-factor modelling. Linear regression was used to test the associations between these dimensions and SZ-PRS, as well as the combined effect of SZ-PRS and cannabis use on the dimensions of positive psychotic symptoms and experiences. We found associations between SZ-PRS and (1) both negative (B = 0.18; 95%CI 0.03-0.33) and positive (B = 0.19; 95%CI 0.03-0.35) symptom dimensions in 617 FEP patients, regardless of their categorical diagnosis; and (2) all the psychotic experience dimensions in 979 controls. We did not observe associations between SZ-PRS and the general and affective dimensions in FEP. Daily and current cannabis use were associated with the positive dimensions in FEP (B = 0.31; 95%CI 0.11-0.52) and in controls (B = 0.26; 95%CI 0.06-0.46), over and above SZ-PRS. We provide evidence that genetic liability to schizophrenia and cannabis use map onto transdiagnostic symptom dimensions, supporting the validity and utility of the dimensional representation of psychosis. In our sample, genetic liability to schizophrenia correlated with more severe psychosis presentation, and cannabis use conferred risk to positive symptomatology beyond the genetic risk. Our findings support the hypothesis that psychotic experiences in the general population have similar genetic substrates as clinical disorders., (© 2021. The Author(s).)

Objectives: Profile characteristics are factors that are relevant for diagnosis, prognosis or treatment. The present study aims to develop a set of clinically relevant profile characteristics. Moreover, our goal is to determine the inter-rater reliability (IRR) of the selected profile characteristics., Methods: Potential profile characteristics were determined by literature review. Assessment of IRR was done by comparing scores on profile characteristics determined by two researchers. We conducted three subsequent studies: (1) assessment of pre-training IRR, (2) IRR following implementation of an instruction manual, (3) IRR after optimizing scoring methods. IRR was measured with the Intraclass Correlation Coefficient (ICC)., Results: IRR scores of profile characteristic Illegal activities were high across the three studies (ICC ≥ 0.75). Following training procedures in study 2 and 3, reliability estimates remained low to moderate (ICC < 0.75) for the profile characteristics Support of relatives, Aggression recent and lifetime, substance use and insight recent. IRR scores of the other eight profile characteristics varied from low, moderate to high across studies., Conclusion: IRR scores of profile characteristics were highly variable, and mostly inadequate in all three studies. Consequently, further research should focus on specification of severity scores of profile characteristics, optimizing scoring methods and re-evaluation of IRR., (© 2020 The Authors. International Journal of Methods in Psychiatric Research published by John Wiley & Sons Ltd.)

Aim: Clinical staging of schizophrenia entails a new method that identifies clusters of symptoms and variation in level of remission, with the goal to create a framework for early intervention. Additionally, duration of untreated psychosis (DUP) may influence symptom severity in the first episode of psychosis (FEP) and could necessitate refining of the staging model. However, consistent evidence concerning variation in symptom severity and DUP between stages is missing. Therefore, we evaluated the clinical validity of the staging model by investigating differences in symptom severity across stages in schizophrenia spectrum disorders. Second, we assessed if a prolonged DUP is associated with higher symptom severity in FEP., Methods: We performed a cross-sectional study of 291 acutely admitted patients with a schizophrenia spectrum disorder. Patients were assigned to clinical stages following the definition of McGorry. Symptom severity was evaluated with the new DSM-5 Clinician-Rated Dimensions of Psychosis Symptom Severity (CRDPSS). In FEP, we determined the DUP., Results: Significantly higher severity scores of CRDPSS items hallucinations (H = 14.34, df = 4, P-value = .006), negative symptoms (H = 19.678, df = 4, P-value = .001) and impaired cognition (H = 26.294, df = 4, P-value = <.001) were found in more advanced stages of disease. Moreover, patients with FEP and a DUP longer than 1 year showed significantly more severe negative symptoms (U = 314 000, P = .015) compared to patients with a DUP shorter than 1 year., Conclusions: The present study found supporting evidence for the clinical validity of the staging model in schizophrenia spectrum disorders. In addition, we found support for refining the stage "first episode" with information concerning the DUP., (© 2020 The Authors Early Intervention in Psychiatry Published by John Wiley & Sons Australia, Ltd.)