Neurodevelopmental disorders and the gut microbiome: insights into ADHD and tic disorders.

This review examines the relationship between tic disorders (TD), attention deficit hyperactivity disorder (ADHD), and the gut microbiota within the framework of the gut-brain axis. We summarize current evidence on the clinical characteristics and neurobiological features of TD and ADHD, and discuss how genetic susceptibility, environmental exposures, and dietary factors may interact with gut microbial composition. We further review studies comparing the gut microbiota of affected individuals and healthy controls, with attention to recurrent taxa-level findings, functional hypotheses, and emerging microbiome-targeted interventions such as probiotics and fecal microbiota transplantation. Importantly, most available human studies remain associative rather than mechanistic, and cross-study comparability is limited by heterogeneity in sequencing approaches, cohort characteristics, medication exposure, and dietary control. Overall, current findings support the gut microbiota as a relevant component of neurodevelopmental disorders such as ADHD and TD, while highlighting the need for larger longitudinal and mechanistic studies to clarify causality and therapeutic potential.