Leisure Screen Time and the Risk of Six Neurodevelopmental Disorders: A Two-Sample Mendelian Randomization Study

Neurodevelopmental disorders (NDDs)-including autism spectrum disorder, attention deficit hyperactivity disorder (ADHD), intellectual disability, learning disability, speech disorder, and Tourette disorder-impact brain development and impair social, learning, and occupational functioning. We performed a Mendelian randomization (MR) analysis using summary data from global genome-wide association studies to investigate the potential causal relationship between leisure screen time (LST) and NDDs risk.

Our dataset comprised 703,901 participants of European ancestry from 51 studies, with 256,725 individuals in the LST-valid sample. We investigated causal associations with six types of NDDs using five MR methods: inverse-variance weighted (IVW), MR Egger, weighted median, simple mode, and weighted mode. IVW was the primary method due to its efficiency and precision. Heterogeneity and horizontal pleiotropy were assessed using IVW and MR Egger, while the other methods served as sensitivity analyses to confirm robustness.

The IVW method revealed that each standard deviation increase in LST was associated with a reduced risk of ADHD (OR = 0.68; 95% CI: 0.52-0.89) and an elevated risk of intellectual disability (OR = 1.66; 95% CI: 1.26-2.18). These associations were consistent with the weighted median analysis (ADHD: OR = 0.68; 95% CI: 0.47-0.98; intellectual disability: OR = 1.51; 95% CI: 1.06-2.14).

Our findings suggest that genetic predisposition to increased LST is causally associated with a lower risk of ADHD but a higher risk of intellectual disability, with no evidence for a causal relatawdionship with the other four NDDs. Larger or longitudinal studies are needed for further validation.