Gut dysbiosis as a driver of neuroinflammation in attention-deficit/hyperactivity disorder: A review of current evidence

Abstract

There is mounting evidence for the involvement of the immune system, neuroinflammation and disturbed gut microbiota, or dysbiosis, in attention-deficit/hyperactivity disorder (ADHD). Gut dysbiosis is strongly implicated in many physical, autoimmune, neurological, and neuropsychiatric conditions, however knowledge of its particular pathogenic role in ADHD is sparse. As such, this narrative review examines and synthesizes the available evidence related to inflammation, dysbiosis, and neural processes in ADHD. Minimal differences in microbiota diversity measures between cases and controls were found, however many relative abundance differences were observed at all classification levels (phylum to strain). Compositional differences of taxa important to key gut-brain axis pathways, in particular Bacteroides species and Faecalibacterium, may contribute to inflammation, brain functioning differences, and symptoms, in ADHD. We have identified one possible model of ADHD etiopathogenesis involving systemic inflammation, an impaired blood–brain barrier, and neural disturbances as downstream consequences of gut dysbiosis. Nevertheless, studies conducted to date have varied degrees of methodological rigour and involve diverse participant characteristics and analytical techniques, highlighting a need for additional research.