Attention-Deficit/Hyperactivity Disorder (ADHD) is a prevalent neurodevelopmental condition in childhood, and growing evidence suggests a potential link between gut microbiome (GM) and ADHD symptoms via the microbiota-gut-brain axis. This systematic review aimed to evaluate current evidence on the associations between human GM and ADHD, addressing microbial composition, diversity measures, and potential pathways through which microbiota could be associated with the symptoms. A systematic search was conducted in PubMed, Embase, and Scopus databases. Fourteen studies met the eligibility criteria, which focused on original research assessing GM characteristics in individuals with ADHD. Selected articles comprised a total of 1319 participants, 67 % male, from Europe (53 %) and East Asia (47 %), mostly with children and adolescents aged 4-18 years. Alterations in microbial composition were observed among ADHD patients; including higher relative abundance of Agathobacter and Ruminococcus gnavus and decreased Faecalibacterium, identified in different studies. Results regarding alpha- and beta-diversity were inconclusive. There was also evidence of links between GM and inflammatory markers and neurotransmitter-related pathways. Despite current limitations, emerging data suggest that GM may play a role in ADHD pathophysiology, supporting its potential as a target for personalized therapeutic strategies.
Gut-Brain Axis