Unveiling causal relationship between white matter tracts and psychiatric disorders.

White matter tracts (WMTs), which mediate information transmission in the brain, are closely associated with the pathogenesis of psychiatric disorders, yet the causality of their associations remain unclear. Thus, we employed two-sample bidirectional Mendelian randomization to explore the causality between WMTs and 10 psychiatric disorders. We found that one standard deviation changes of WMTs metrics modified risks for 8 psychiatric disorders by 2·2% to 71·4%. For example, increased fornix/stria terminalis radial diffusivities elevated PTSD risk by 8.3%, while heightened mode anisotropy reduced Tourette syndrome risk by 71.4%. Reversely, alcohol use disorder increased the risk of WMTs abnormalities. Our study provides novel insights into the potential causality between WMTs and psychiatric disorders, indicating that alterations of WMTs may serve as biomarkers for psychiatric disorders.