Assessing the causal association between celiac disease and autism spectrum disorder: A two-sample Mendelian randomization approach.

The association between celiac disease (CD) and autism spectrum disorder (ASD) remains inconclusive. Reports from different observational studies have become controversial, necessitating exploration of the causal relationship between CD and ASD. To assess true causality, this study used a two-sample Mendelian randomization (MR) analysis to determine the causal association between CD and ASD. Summary-level data from a genome-wide association study (GWAS) of the European population were used to select instrument variables (IVs) at genome-wide significance (p < 5 × 10). The strength of IVs was also evaluated with F-statistics. The inverse variance weighted method (IVW) was the primary MR analysis, supported by other MR tests such as the weighted median method and weighted mode. The presence of horizontal pleiotropy was tested with MR-Egger and MR-PRESSO while other sensitivity analyses such as heterogeneity, leave-one-out analysis, and scatterplot were used to assess the validity of our MR results. Our study did not show an association between CD and ASD (OR, 0.994; 95% CI, 0.935-1.057; p = 0.859). There was also no evidence of horizontal pleiotropy (MR-Egger intercept = 0.015; p-value = 0.223) and heterogeneity (Q = 14.029; p-value = 0.051). These results were also complemented by the leave-one-out analyses, forest plot, and scatter plot, which showed that none of the SNPs influenced the result. The result of this study shows that CD is not causally associated with ASD.