Fecal transplant (FMT) and autism spectrum disorder

Development of the therapy

Up to 70% of children with autism spectrum disorder (ASD) have chronic GI symptoms — constipation, diarrhoea, abdominal pain — and have systematically different gut microbial communities than neurotypical peers. In 2017, Kang and colleagues at Arizona State University ran an open-label trial of MTT (vancomycin pre-treatment, bowel cleanse, then high-dose oral and rectal FMT followed by 7–8 weeks of maintenance) in 18 children. GI symptoms improved by ~80% and the improvement persisted at 2-year follow-up, alongside measurable reductions in autism behavioural scores.¹²

Therapeutic target

The hypothesis is the gut–brain axis: an altered microbiome may influence neurodevelopment and behaviour through neuroactive metabolites (short-chain fatty acids, tryptophan derivatives), vagal signalling, and immune modulation. Children with ASD show reduced microbial diversity and depletion of fermentative bacteria. MTT aims to engraft a more diverse community and shift metabolite production.³

What the trials show

• Open-label, single-centre. The strongest data come from one research group and ~20 participants, without a placebo or sham-FMT control.
• GI improvements of roughly 80% on the GSRS scale, sustained at 2 years.
• Behavioural improvements of ~24% on the Childhood Autism Rating Scale at 2 years, exceeding what would be expected from natural history.
• Microbiome engraftment of donor strains was demonstrated and partially persisted.
• Larger, randomised, sham-controlled trials are underway. Until they read out, FMT for autism remains investigational.

Possible side effects and risks

• Transient GI symptoms in the first days, similar to FMT in other indications
• The MTT protocol uses 14 days of oral vancomycin, which carries its own selection pressure on the microbiome and rare adverse effects
• Sedation/procedural risks if the lower-gut dose is given by colonoscopy
• Unknown long-term effects of donor microbiome engraftment in children
• The FDA has explicitly warned against unregulated, home, or commercial FMT in this population

FAQ: FMT in autism

The current evidence is encouraging but preliminary. Decisions about participation in research should be made with the child's paediatrician and developmental specialist.

References

1. Kang DW, et al. Microbiota Transfer Therapy alters gut ecosystem and improves gastrointestinal and autism symptoms: an open-label study. Microbiome. 2017.
2. Kang DW, et al. Long-term benefit of Microbiota Transfer Therapy on autism symptoms and gut microbiota. Sci Rep. 2019.
3. Cryan JF, et al. The Microbiota–Gut–Brain Axis. Physiol Rev. 2019.