Quantitative and qualitative symptomatic differences in individuals at Ultra-High Risk for psychosis and healthy controls.

Patients at Ultra-High Risk (UHR) for developing a first psychosis vary widely in their symptom presentation and illness course. An important aim in UHR research concerns the characterization of the clinical heterogeneity in this population. We aimed to identify qualitatively and quantitatively different clinical symptom profiles at baseline and at 2-year follow-up in a group of UHR subjects and healthy controls. We employed a Latent Class Factor Analysis (LCFA) to the 19 items of the Structured Interview for Prodromal Syndromes (SIPS) ratings at baseline and at 2-year follow-up in a sample of 147 UHR subjects and 141 controls from the Dutch Prediction of Psychosis Study (DUPS) in the Netherlands. Additionally, a stepwise logistic regression analysis was performed with transition to psychosis as a dependent variable and baseline latent variable scores as predictors. Variation in symptomatology at baseline was explained by both quantitative and qualitative differences; at 2-year follow-up qualitative differences between individuals were no longer observed. Quantitative differences showed moderate stability over time (range=0.109-0.42). Within the UHR sample, transition to psychosis was significantly associated with quantitative differences in baseline SIPS scores. The results of our study suggest a 'quasi'-continuous extended psychosis phenotype, a finding that merits replication in other samples.