Causal Relationship between White Matter Tracts and Psychiatric Disorders: A Mendelian Randomization Study

White matter tracts (WMTs), which are responsible for information transmission in the brain, are closely associated with the onset, development, and prognosis of psychiatric disorders, yet the underlying causal mechanisms of their associations remain largely unclear. Thus, we employed two-sample bidirectional Mendelian randomization (MR) to explore the causality between WMTs and 10 psychiatric disorders. The sample sizes of summary-level datasets were ranged from 14,307 to 1,222,882. We found that changes in WMTs are associated with the risk of 8 types of psychiatric disorders, one standard deviation change in WMTs can increase or reduce the risk of psychiatric disorders by 2.2–71.4%. In the reverse MR analysis, we discovered that alcohol use disorder also increases the probability of specific WMT abnormalities. Our study provides novel insights into the potential causal association between WMTs and psychiatric disorders, indicating that specific characteristics of WMTs may serve as potential biomarkers for psychiatric disorders.