The role of circadian rhythms and sleep in the aetiology of autism spectrum disorder and attention-deficit/hyperactivity disorder: New evidence from bidirectional two-sample Mendelian randomization analysis

Increasing evidence highlights the role of disrupted circadian rhythms in the neural dysfunctions and sleep disturbances observed in autism spectrum disorder and attention-deficit/hyperactivity disorder. However, the causality and directionality of these associations remain unclear. In this study, we employed a bidirectional two-sample Mendelian randomization framework, leveraging genome-wide association study data from the UK Biobank ( n = 85,670) and FinnGen ( n = 377,277). Genetic variants served as instrumental variables to infer causation, and objective accelerometer-derived metrics identified circadian rhythm and sleep genetic instruments. The results showed that the timing of the most active 10 h was significantly linked to higher odds of autism spectrum disorder and attention-deficit/hyperactivity disorder. Independently, higher sleep efficiency predicted a lower risk of autism spectrum disorder, while attention-deficit/hyperactivity disorder was linked to an increase in nocturnal sleep episodes. Heterogeneity and sensitivity analyses confirmed these findings. Our study establishes causal links between circadian alterations and autism spectrum disorder and attention-deficit/hyperactivity disorder, distinguishing the independent and protective role of sleep efficiency in autism spectrum disorder from circadian rhythms. In attention-deficit/hyperactivity disorder, however, disrupted sleep appears as a consequence, not a cause. These insights highlight divergent interactions with sleep factors in autism spectrum disorder and attention-deficit/hyperactivity disorder, laying the groundwork for tailored therapeutic strategies that recognize the distinct influences of sleep quality and circadian rhythms in each disorder. Lay abstract Research shows that people with autism spectrum disorder and attention-deficit/hyperactivity disorder often have sleep issues and problems with the body’s natural daily rhythms, known as circadian rhythms. By exploring the genetic variants associated with these rhythms and the conditions, this study reveals that these rhythm changes and sleep patterns are directly linked to autism spectrum disorder and attention-deficit/hyperactivity disorder. It found that the timing of one’s most active hours can increase the likelihood of having both autism spectrum disorder and attention-deficit/hyperactivity disorder. Importantly, it also shows that good sleep quality might protect against autism spectrum disorder, while disturbed sleep in people with attention-deficit/hyperactivity disorder seems to be a result rather than the cause of the condition. This understanding can help doctors and researchers develop better treatment approaches that focus on the specific ways sleep and body rhythms affect those with autism spectrum disorder and attention-deficit/hyperactivity disorder, considering their unique associations with circadian rhythms and sleep patterns. Understanding these unique links can lead to more effective, personalized care for those affected by these conditions.