54. Neurobiological Correlates of Symptom Dimensions in Individuals at Ultra High Risk for Psychosis

Background: The Ultra High Risk (UHR) state is a combination of genetic and clinical risk factors that are associated with an imminent high risk for psychotic disorder. Clinical features in UHR individuals are assessed using specialized semistructured interviews, such as the Comprehensive Assessment of At Risk Mental State (CAARMS). Previous studies have found that the range of symptoms measured by the CAARMS can be reduced to underlying symptom dimensions and these underlying psychopathological dimensions have been linked to higher risk of transition to psychosis, however neither of the two alternative factor structures in UHR have been replicated and to date there has been no investigation of the neurobiological correlates of symptom dimensions in UHR. Methods: CAARMS data for 500 UHR subjects from 10 different countries was split randomly in to two to perform principle axis factoring (PAF) on one half, and confirmatory factor analysis (CFA) of structures previously found in the literature and any structure found through PAF on the other half. Scores for each factor of the structure found to best fit the data were then correlated with clinical outcome and resting regional cerebral blood flow (rCBF) attained through pseudo-continuous arterial spin labelling imaging in a subset of 90 UHR. Results: PAF revealed a 5-factor structure accounting for 41% of the variance. CFA showed neither of the two factor structures found in the literature fit the data, but the 5-factor structure found through PAF showed statistical goodness of fit (χ 2 = 6.18 (1298.01), P < .05; RMSEA = 0.058 [90% CI = 0.04, 0.07]; CFI =0.90). Correlation of factor scores with clinical outcome and rCBF is ongoing, however preliminary analysis show increased midbrain rCBF in the transition group. Conclusion: A five factor structure has been found in the largest sample of UHR to date, and confirmed in an independent data set. We hope to show a correlation of the negative/disorganized dimension with transition to psychosis, and an inverse correlation with rCBF in frontal and parietal regions as found previously in the literature. A dimensional approach to UHR symptomatology could better understand clinical vulnerability and enable patient tailored assessment and treatment in a notoriously heterogeneous group.