Supplementary Material for: Sterol Regulatory Element Binding Transcription Factor-1 Gene Variation and Medication Load Influence White Matter Structure in Schizophrenia

Background: Diffusion tensor imaging (DTI) studies have shown a widespread disruption of white matter (WM) microstructure in schizophrenia. Furthermore, higher fractional anisotropy (FA) has been consistently correlated with the severity of psychotic symptoms. Antipsychotic drugs (APDs) affect lipid homeostasis. Gene polymorphisms in sterol regulatory element binding transcription factor (SREBF)-1 and SREBF-2 have been associated with schizophrenia. Methods: In a sample of 65 patients affected by chronic schizophrenia, we investigated the effect of ongoing APD medication, SREBF-1 rs11868035 polymorphism and SREBF-2 rs1052717 polymorphism on the WM microstructure, using tract-based spatial statistics with threshold-free cluster enhancement. Results: We reported increased FA associated with the risk rs11868035 G/G genotype in several WM tracts, mainly located in the left hemisphere, and opposite effects of the APD medication load, with reduced FA and generally increased diffusivity. These opposite effects overlapped in the forceps minor, cingulum, uncinate fasciculus, the superior and inferior longitudinal fasciculi, the corticospinal tract, inferior fronto-occipital fasciculus and the anterior thalamic radiation. Conclusion: We suggest that changes of WM structure could be an as yet poorly explored biomarker of the effects of APDs, to be further investigated in prospective studies correlating long-term clinical effects with changes of DTI measures in specific WM tracts contributing to the functional integrity of the brain.