Causal associations between gut microbiota and autism spectrum disorder and attention-deficit/hyperactivity disorder: a two-sample mendelian randomization study.

Background: The gut microbiota have been implicated in the development of autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD). However, the precise causal relationships between the gut microbiota and ASD or ADHD remain unclear. Methods: We investigated potential causal associations between gut microbiota and two neurodevelopmental mental disorders (ASD and ADHD) via Mendelian randomization (MR) analyses. We used genome-wide association study (GWAS) summary datasets, including data from the MiBioGen consortium (N = 18,340), the Dutch Microbiome Project (N = 8,208), an ASD GWAS (N = 46,350), and an ADHD GWAS (N = 292,548). Results: Our MR analysis identified 16 gut bacterial taxa associated with ASD. Seven taxa were associated with an increased risk (OR 1.03-1.10), while nine were associated with a decreased risk (OR 0.89-0.96). Conversely, 28 gut bacterial taxa were causally linked to ADHD: 16 were associated with an increased risk (OR 1.02-1.04), and 12 were associated with a decreased risk (OR 0.95-0.98). Both ASD and ADHD were causally influenced by the family "Clostridiales noname," but with opposite effects. Conclusion: Our MR analysis revealed causal effects of specific gut microbiota on ASD and ADHD, suggesting that certain gut microbes may play a role in the development and treatment of these disorders, as well as in their differential diagnosis.