Causal Associations of Sleep Apnea with Alzheimer's Disease and Cardiovascular Disease: a Bidirectional Mendelian Randomization Analysis

BackgroundSleep apnea (SA) has been linked to an increased risk of dementia in numerous observational studies; whether this is driven by neurodegenerative, vascular or other mechanisms is not clear. We sought to examine the bidirectional causal relationships between SA, Alzheimers disease (AD), coronary artery disease (CAD), and ischemic stroke using Mendelian randomization (MR). MethodsUsing summary statistics from four recent, large genome-wide association studies of SA (n=523,366), AD (n=64,437), CAD (n=1,165,690), and stroke (n=1,308,460), we conducted bidirectional two-sample MR analyses. Our primary analytic method was fixed-effects inverse variance weighted MR; diagnostics tests and sensitivity analyses were conducted to verify the robustness of the results. ResultsWe identified a significant causal effect of SA on the risk of CAD (odds ratio (ORIVW) =1.35 per log-odds increase in SA liability, 95% confidence interval (CI) =1.25-1.47) and stroke (ORIVW=1.13, 95% CI =1.01-1.25). These associations were somewhat attenuated after excluding single-nucleotide polymorphisms associated with body mass index (BMI) (ORIVW=1.26, 95% CI =1.15-1.39 for CAD risk; ORIVW=1.08, 95% CI =0.96-1.22 for stroke risk). SA was not causally associated with a higher risk of AD (ORIVW=1.14, 95% CI =0.91-1.43). We did not find causal effects of AD, CAD, or stroke on risk of SA. ConclusionsThese results suggest that SA increased the risk of CAD, and the identified causal association with stroke risk may be confounded by BMI. Moreover, no causal effect of SA on AD risk was found. Future studies are warranted to investigate cardiovascular pathways between sleep disorders, including SA, and dementia.