Daytime sleepiness might increase the risk of ALS: a 2-sample Mendelian randomization study

Background Observational studies have indicated that there is a high prevalence of habitual sleep disturbances in amyotrophic lateral sclerosis (ALS). However, the actual relationship between these symptoms and ALS remains unclear. Methods We used 2-sample Mendelian randomization to determine whether the sleep disturbances associated with ALS are also related to the risk of ALS. The summary statistics we used were from recent, large genome-wide association studies on daytime sleepiness and other night sleep traits (n = 85,670-452,071) and ALS (n = 20,806 cases, n = 59,804 controls). The inverse variance-weighted (IVW) method was used as the main method for assessing causality. Results Daytime sleepiness might increase the risk of ALS (IVW odds ratio = 2.45, 95% confidence interval: 1.15-5.21; P = 0.020). ALS was not associated with sleep efficiency, number of sleep episodes or sleep duration. Conclusions Our results provide novel evidence that daytime sleepiness increases the risk of ALS and points out the importance of daytime sleepiness that often goes unnoticed in ALS.