Transdiagnostic Symptom Dimensions in Individuals at Ultra-High Risk for Psychosis: Towards Dimensional Representations of Pluripotent Risk

Intro: Research has shifted focus from categorical to dimensional conceptualizations of mental health conditions. This is supported by high overlap between disorders, particularly psychosis spectrum and affective disorders, which cuts across traditional diagnostic boundaries. While there is evidence for a general factor of psychopathology in individuals with schizophrenia, schizoaffective disorder, and psychotic bipolar I disorder, transdiagnostic dimensions of psychopathology have not been investigated in young individuals at Ultra-High Risk (UHR) for psychosis. The current study sought to investigate (1) whether there is a general dimension underlying psychopathological symptoms in UHR individuals and (2) whether the formation of specific symptom dimensions (positive symptoms, negative symptoms, affect, and activation) is justified alongside a general dimension. Methods: Item factor analyses were conducted on symptom ratings of the Brief Psychiatric Rating Scale at baseline in the Staged Treatment in Early Psychosis (STEP) trial. Results: In total, 342 UHR participants were included. A bifactor model with one general symptom dimension and four specific factors of positive symptoms, negative symptoms, affect, and activation yielded the best relative model fit and interpretability when compared to uni- and multidimensional models, albeit absolute model fit statistics provided no strong evidence to support this finding. However, model stability and interpretability tentatively support its utility in addressing our aims of disentangling pluripotent from domain-specific dimensions. Conclusion: These findings shed light on the dimensionality of symptoms in youth at UHR for psychosis and reflect an important step towards dimensional phenotypes in hierarchical models of psychopathology.