Autism and the Oral Microbiome: A Systematic Review of Host-microbial Interactions and Diversity

Sep 10, 2025International dental journal

Autism and the Mouth Microbiome: A Review of Microbe Interactions and Diversity

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Gut-Brain Axis on OpenScience ↗PubMed ↗DOI ↗

Abstract

Nine studies involving 8533 participants explored the association between the oral microbiome and autism spectrum disorder (ASD).

Microbial diversity findings in ASD were inconsistent across studies, with some reporting alterations and others showing no significant differences.
Functional analysis indicated an enrichment of pathways related to dopamine and GABA breakdown, along with disruptions in lysine metabolism.
These metabolic changes may be related to neurotransmitter imbalances observed in ASD.
External factors, such as selective eating and oral hygiene, were suggested to influence microbial profiles, but robust statistical support for these associations was lacking.
No consistent connections were identified between oral microbiota characteristics and core ASD symptoms, such as repetitive behaviors or communication deficits.

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BACKGROUND: Emerging evidence suggests a link between the oral microbiome and autism spectrum disorder (ASD), a neurodevelopmental condition characterised by social and behavioural impairments. The vast microbial reservoirs in the gut complement those of the oral cavity, suggesting a potential oral-gut-brain axis that may influence ASD and perhaps other neurological diseases, such as Parkinson's syndrome and Alzheimer's disease. For the first time, this systematic review synthesises the current knowledge of oral microbiome composition, diversity, and functionality in ASD and its potential diagnostic and therapeutic implications.

METHODS: A comprehensive literature search was conducted using Medline (PubMed), Embase, Scopus, and Google Scholar for peer-reviewed case-control and cross-sectional studies published between January 2000 and January 2025. Study quality was assessed using the Newcastle-Ottawa scale.

RESULTS: Nine studies (n = 8533; 2536 ASD and 5937 controls) met the inclusion criteria. The overall findings on microbial diversity were inconsistent; some studies reported alterations in ASD, while others found no significant differences. Functional profiling revealed enrichment of pathways involved in dopamine and GABA degradation, as well as disruptions in lysine metabolism, suggesting possible links to neurotransmitter imbalances in ASD. Although external factors such as selective eating, oral hygiene, and cognitive function were proposed to influence microbial profiles, statistical evidence supporting these associations was lacking. Moreover, no consistent link was found between oral microbiota features and core ASD symptoms like repetitive behaviours or communication deficits.

CONCLUSION: This review highlights subtle yet potentially significant alterations in the oral microbiome of individuals with ASD, particularly in metabolic pathways that affect neurotransmitters. While direct associations with clinical symptoms remain unsubstantiated, the findings emphasise the importance of future multi-omics and longitudinal studies to clarify the oral microbiome's role in ASD pathophysiology and to explore its potential in personalised therapeutic strategies.