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

Extensive studies put forward the association between Alzheimer's disease (AD) and psychiatric disorders; however, it remains unclear whether these associations are causal.

We aimed to assess the potential causal relationship between major psychiatric disorders and AD.

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.

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].

There is no significant evidence supporting the causal association between the five major psychiatric disorders and AD.