Five Major Psychiatric Disorders and Alzheimer's Disease: A Bidirectional Mendelian Randomization Study

Background: Extensive studies put forward the association between Alzheimer's disease (AD) and psychiatric disorders; however, it remains unclear whether these associations are causal. Objective: We aimed to assess the potential causal relationship between major psychiatric disorders and AD. Methods: A bidirectional two-sample Mendelian randomization (MR) was applied to evaluate potential causality between five psychiatric disorders and AD by selecting the single-nucleotide polymorphisms from the genome-wide association studies as instrumental variables. Inverse-variance weighted (IVW) method was used as the main analyzing approach to estimate possible causal effects, alternative methods including MR-Egger, the MR pleiotropy residual sum and outlier, and leave-one-out analysis method were implemented as sensitivity analyzing approaches to ensure the robustness of results. Results: All forward and reverse MR analyses consistently suggested absent causal relations between psychiatric disorders and AD risk [forward IVW: ORADHD, 1.030, 95% CI, 0.908-1.168, p = 0.674; ORanxiety disorders, 0.904, 95% CI, 0.722-1.131, p = 0.377; ORASD, 0.973, 95% CI, 0.746-1.272, p = 0.846; ORBIP, 1.033, 95% CI, 0.925-1.153, p = 0.564; and ORschizophrenia, 1.039, 95% CI, 0.986-1.095, p = 0.156; reverse IVW: ORADHD, 0.993, 95% CI, 0.954-1.034, p = 0.746; ORanxiety disorders, 1.000, 95% CI, 0.999-1.000, p = 0.898; ORASD, 1.001, 95% CI, 0.962-1.042, p = 0.949; ORBIP, 0.997, 95% CI, 0.966-1.028, p = 0.831; and ORschizophrenia, 1.013, 95% CI, 0.978-1.051, p = 0.466]. Conclusion: There is no significant evidence supporting the causal association between the five major psychiatric disorders and AD.