• Research
• Expressions Summer 2025

New Frontier for Autism Diagnosis

Mouth microbes may serve as early markers of autism spectrum disorder

From left: Dr Charles Cheuk-fung Hau, Professor Kathy Kar-man Shum, Senior Lecturer and PhD candidate Jacqueline Wai-yan Tang from the Department of Psychology; Professor Cynthia Kar Yung Yiu and Professor Rory Munro Watt from the Faculty of Dentistry.

A cross-disciplinary HKU team from the Faculty of Dentistry and the Department of Psychology in the Faculty of Social Sciences has uncovered a link between the composition of the microbial community living in the mouth (oral microbiota) and autism spectrum disorder (ASD). Their finding that young children with ASD exhibit markedly different profiles of oral bacteria from their neurotypical peers offers a new path for microbiota-based ASD screening that could enable earlier diagnosis and developmental care.

Affecting 1 in 36 children in the United States and 1 in 49 in Hong Kong, ASD is a lifelong neurodevelopmental condition typified by restricted, repetitive behaviours and challenges with social communication. Current diagnostic practices are largely based on subjective observation around the age of 5 years, which misses a critical developmental window when interventions would be most impactful. In the search for earlier and more objective ASD screening methods, the gut microbiota has been previously explored; yet, the oral microbiota has remained largely overlooked, until now.

The HKU team behind the new study, published in January 2025 in the Journal of Dentistry, consisted of Professor Cynthia Yiu, Associate Professor Rory Watt, Dr Charles Hau, and Mr Raymond Tong at the Faculty of Dentistry, and Senior Lecturer Jacqueline Tang and Associate Professor Kathy Shum at the Department of Psychology.

A dentist performs an oral examination on a child participant, collecting her dental plaque samples.

The team studied the variety of bacteria present in dental plaque—the sticky layer covering teeth—in two groups of Hong Kong children aged 3–6 years: 25 children with ASD and 30 age- and sex-matched neurotypical children. Genetic analysis (16S rRNA gene sequencing) revealed fewer types of bacteria in the ASD group and identified 11 species of bacteria that could serve as potential biomarkers to help tell the groups apart: six species were unique to the ASD group and five were unique to the neurotypical group. A predictive model built on the bacterial profile data achieved a high accuracy, of 81%, in distinguishing between children with and without ASD.

Referring to the microbiome as the genetic material and environment of microbes, the researchers conclude: “These findings contribute to understanding the microbiome–brain connection in ASD and its implications for early detection and management. Further research is needed to validate these oral bacterial biomarkers and explore their mechanistic association with ASD pathophysiology.”

This research marks an important first step towards creating a simple, non-invasive diagnostic tool for ASD screening, prior to professional evaluation. The team is now recruiting a larger pool of participants to confirm their initial findings and to improve their predictive tool.

Their long-term vision is to transform children’s routine dental visits into opportunities to collect oral swabs for microbial profile analysis. This novel and innovative approach to ASD screening would allow early autism detection and help improve quality of life for affected children and their families.