The objective of this study is to conduct a open-label pilot study evaluating the feasibility, tolerability and preliminary efficacy of a 12-week course of synbiotic in improving anxiety symptoms in children with ASD. The investigators hypothesise that the course of synbiotic will feasible and tolerable, and that there will be a reduction in anxiety symptoms in ASD children after the 12-week course of synbiotic.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder defined by the core features of social communication deficits and restricted and repetitive behaviour (RRB). One important treatment target of ASD children is co-occurring neuropsychiatric disorders, which would interact with the core symptoms to further jeopardize their social and educational development. In pre-pubertal children, anxiety disorder is one of the commonest co-occurring psychiatric disorders without effective therapeutics. Anxiety symptoms is related to sensory hyperresponsiveness, and emerging evidence has shown that sensory atypicality in ASD could be contributed by the altered gut microbiota. Thus, intervention that targets the gut microbiota may improve the clinical anxiety symptoms in ASD children.

In this study, a pilot open-label trial will be conducted. It is planned that 30 ASD children who are below 12 years of age will be recruited from a regional children psychiatric specialist clinic to undergo a 12-week course of synbiotic. Feasibility, tolerability and preliminary efficacy of the synbiotic will be investigated using standardised parent-filled questionnaires. Changes in fecal microbiome and metabolites will be observed. The outcomes will be measured at weeks 6 and 12 of the 12-week course of synbiotic.

The results of the proposed study will provide insights with regards to the design and implementation of the main randomised controlled trial (RCT), contributing to the generation of evidence to the real-life efficacy the synbiotic. Physiological measurements of gut metagenomics and metabolomics will shed light on the specific mechanisms underlying clinical efficacies, which could inform the development of novel therapeutics targeting the microbiota-gut-brain axis in ASD.

Inclusion Criteria:

1. ASD children of Chinese ethnicity aged <12 with diagnosis made by child psychiatrists based on Diagnostic and Statistical Manual, Fifth Edition (DSM-5) diagnostic criteria.
2. Elevated anxiety level, as measured by Anxiety Scale for Children-Autism Spectrum Disorder (ASC-ASD)
3. Presence of sensory hyperresponsiveness, as measured by Sensory Experience Questionnaire (SEQ)

Exclusion Criteria:

1. Co-occurring mental retardation, neurological, psychosis, depression or other severe mental illness.
2. History of non-functional gastrointestinal disorders such as inflammatory bowel disease and Hirschsprung's disease.
3. Presence of other significant physical illness, including but not limited to: current active malignancy, immunosuppression, organ failure and epilepsy
4. Exposure to antibiotics within 1 months of the study or history of using probiotics.
5. On special diet such as being a vegetarian