Washed microbiota transplantation improves clinical symptoms, gut microbiota, and metabolic profiles in autism spectrum disorder in a twin cohort.

Objective: Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental condition characterized by impaired social communication, repetitive behaviors, and restricted interests. Dysregulation of the microbiota-gut-brain axis is closely associated with the pathogenesis of ASD. Washed microbiota transplantation (WMT) has emerged as a promising intervention for ASD, but existing cohort studies lack genetically identical controls, making it difficult to distinguish intervention-related changes from genetic and environmental confounding factors. This twin-paired controlled study adopted a study design that minimizes the influence of genetics and shared environment, to explore the associations of WMT with clinical symptoms, gut microbiota, and metabolic profiles in children with ASD. Methods: Three pairs of age- and environment-matched twins (one ASD-affected, one typically developing sibling) were enrolled. WMT was administered to the ASD participant in each pair. Fecal samples were collected at baseline and post-intervention. Gut microbiota and metabolic profiles were analyzed using metagenomic sequencing and targeted metabolomics, respectively. Clinical outcomes were evaluated using the Childhood Autism Rating Scale (CARS), Autism Behavior Checklist (ABC), Sleep Disturbance Scale for Children (SDSC), and Bristol Stool Form Scale (BSFS). Relevant observations were carried out to explore potential changing trends. Results: After WMT, CARS, ABC, SDSC, and BSFS exhibited small numerical directional shifts toward healthier values, but none reached statistical significance. Gut microbial structure and function presented a shifting trend toward the profile of their typically developing twin siblings. Abnormal lipid and energy metabolism indicators showed partial ameliorative trends, and the number of differential metabolites between ASD patients and healthy siblings was markedly reduced. Tyrosine and phenylalanine metabolic pathways, together with Limitations: Although the twin-pair design has high internal validity and can provide strong causal inference evidence for the effect of microbiota transplantation in treating ASD, this study has limitations such as a small sample size, a single-center non-randomized observational design. All findings in this pilot study are merely descriptive trends, and the relevant mechanism analysis only provides correlational clues. A single session of microbiota transplantation failed to fully adjust aromatic amino acid metabolism in ASD children. No definitive causal relationship can be concluded based on the findings of this small-sample pilot study. Conclusion: Under tightly controlled genetic and environmental conditions, gut microbial dysbiosis presents correlational characteristics with ASD-related phenotypes. WMT was associated with consistent remodeling of gut microbial ecology and partial resolution of metabolic dysregulation in ASD children, with multi-omic signatures converging toward healthy twins. Clinical rating scales only displayed non-significant minor numerical shifts, which cannot be interpreted as evidence of clinical symptom improvement. These initial findings provide exploratory mechanistic clues and phenotypic data supporting WMT as a targeted microbiome intervention approach for ASD, and await further validation through large-scale randomized controlled trials. Clinical trial registration: Identifier ChiCTR2400091105.