Differential time course of microstructural white matter in patients with psychotic disorder and individuals at risk: A 3-year follow-up study

Background: Although widespread reduced white matter (WM) integrity is a consistent finding in crosssectional diffusion tensor imaging (DTI) studies of schizophrenia, little is known about the course of these alterations. This study examined to what degree microstructural WM alterations display differential trajectories over time as a function of level of psychosis liability. Methods: Two DTI scans with a 3-year time interval were acquired from 159 participants (55 patients with a psychotic disorder, 55 nonpsychotic siblings and 49 healthy controls) and processed with tract-based spatial statistics. The mean fractional anisotropy (FA) change over time was calculated. Main effects of group, as well as group × region interactions in the model of FA change were examined with multilevel (mixed-effects) models. Results: Siblings revealed a significant mean FA decrease over time compared to controls (B = -0.004, P = .04), resulting in a significant sibling-control difference at follow-up (B = -0.007, P = .03). Patients did not show a significant change over time, but their mean FA was lower than controls both at baseline and at followup. A significant group × region interaction (χ² = 105.4, P = .01) revealed group differences in FA change in the right cingulum, left posterior thalamic radiation, right retrolenticular part of the internal capsule, and the right posterior corona radiata. Conclusion: Whole brain mean FA remained stable over a 3-year period in patients with psychotic disorder and declined over time in nonaffected siblings, so that at follow-up both groups had lower FA with respect to controls. The results suggest that liability for psychosis may involve a process of WM alterations.