A Review of the Research: What Does it Say About Autism and FMT?


By: Dr. Shaina Cahill, Ph.D. (Director Medical Communications & Affairs)

The incidence rate of Autism Spectrum Disorder (ASD) diagnosis continues to rise; the US Centers for Disease Control and Prevention reports that the diagnosis of ASD in children today is 1 in 54 compared to 1 in 150 children in 2000 1–4. This increase in ASD diagnosis is not specific to the US, with the incidence of ASD in China also being reported to have increased from 2.8 per 10,000 in 2000 to 63 per 10,000 in 2015 5–7. Currently, no medical treatments have been approved to treat core symptoms of ASD, such as social communication difficulties and repetitive behaviours.

As we look to better understand ASD and its core symptom presentation, the connection between the gut and autism has become a focus. Children with autism are reported to have more gastrointestinal (GI) issues and an altered gut microbiome compared to typically developing (TD) children 2,5,8–23. These findings have motivated an exploration into the connection between the gut microbiome and ASD, with multiple studies supporting a strong relationship between behavioural and GI symptoms 2,8,13,20,24–36; learn more about the relationship between the gut microbiome and ASD HERE.

Fecal Microbiota Transplant (FMT) is a medical procedure being studied across many disease states that are the result of a damaged or unhealthy gut microbiome 37–41. Researchers have found that many factors like delivery method, diet and medications such as antibiotics can negatively impact our gut microbiota resulting in an unhealthy gut microbiome 5,42–63(learn more about what can damage the microbiome HERE). FMT is the infusion of specially prepared stool material from a healthy donor(s) into the gut (intestinal tract) of a recipient to restore a healthy and stable microbial community and confer health benefits and/or treat a specific disease or symptom(s) 39,41,64,65. The idea here is that FMT will help re-educate the recipient’s gut microbiome, inducing the re-colonization of the gut and restort microbial diversity to donor-like proportions 66–71 (Check out these links to learn more about FMT).

Though there is still a need for more randomized clinical trials, there is some promising clinical research focused on ASD and manipulating the gut microbiome through FMT. While to what extent core behavioural symptoms correlate with, predict, or are predicted by the gut microbiome is unknown, the use of FMT has shown considerable potential in children with ASD. Generally, these studies have found that FMT treatment in children with ASD leads to:

  1. Improvements in gastrointestinal symptoms 15,72,73
  2. Improvements in autism-related symptoms 15,72,73
  3. A shift in the gut microbiome towards TD children 15,72–75
  4. Changes in neurotransmitters levels 73,75
  5. Changes in ASD severity 72

Below are some highlighted clinical studies:

Dr. James Adams’ group for Arizona State University (ASU) performed a series of studies examining the long-term beneficial effects for children diagnosed with ASD through FMT.

1. Microbiota Transfer Therapy alters gut ecosystem and improves gastrointestinal and autism symptoms: an open-label study 15

This initial study utilized a modified FMT protocol, termed Microbiota Transfer Therapy (MTT), for children with ASD and chronic GI issues. MTT consisted of a 2-week vancomycin treatment (antibiotics) followed by a bowel cleanse pre-treatment. FMT consisted of 1-2 days of high dose FMT followed by 7–8 weeks of daily maintenance doses with a stomach acid suppressant. An 8-week follow-up period (18 weeks in total) was used to evaluate the long-lasting effects of FMT. Their principal findings were:

i.   FMT improves GI symptoms with Gastrointestinal Symptoms Rating Scale (GSRS) scores decreasing by 77% from baseline and significant improvements in stool type and frequency.

ii.    ASD symptoms showed improvements with a 23% decrease in Childhood Autism Rating Scale (CARS) scores from baseline.
iii.     FMT significantly increased the bacterial diversity in the gut, which became indistinguishable between the ASD and TD peers by week 18. Gut bacteria were significantly less diverse in children with ASD than TD controls at baseline, which was significantly improved post-FMT.  

  1. Long-term benefit of Microbiota Transfer Therapy on autism symptoms and gut microbiota 72

This study consisted of a 2-year follow-up on patients from their original 2017 study; their major findings were:

i. Two years after treatment, most participants reported GI symptoms remaining improved compared to baseline. An average of a 58% reduction in Gastrointestinal Symptom Rating Scale (GSRS) and 26% reduction in percent days of abnormal stools (Daily Stool Record or DSR) relative to baseline was reported.

ii. Families reported that ASD-related symptoms had slowly and steadily improved over the 2 years. Autism-related symptoms improved even more after the end of treatment. Based on the Childhood Autism Rating Scale (CARS), the severity of ASD at the two-year follow-up was 47% lower than baseline, compared to 23% lower at the end of the initial trial.

iii.     At the beginning of the original trial, 83% of participants rated as severe ASD on the CARS assesment. At the two-year follow-up, only 17% were rated as severe, 39% were in the mild to moderate range, and 44% of participants were below the ASD diagnostic cut-off scores on the CARS.

iv.    Improvements in GI and ASD-related symptoms were significantly correlated, such that changes in CARS scores were positively correlated with changes in GSRS scores. This implies that GI symptoms improvements provided by FMT may improve the severity of behaviours in children with ASD.  

v. Important changes in gut microbiota at the end of treatment remained at follow-up, with fecal bacterial diversity higher two years after treatment.

Dr. Yanling Wei’s group performed a 2021 study entitled, Fecal Microbiota Transplantation Relieves Gastrointestinal and Autism Symptoms by Improving the Gut Microbiota in an Open-Label Study 73. This study consisted of a 12-week protocol including 4 weeks of FMT and an 8-week follow-up period. This study stands out because no pre-treatment, using antibiotics or proton pump inhibitors was performed before FMT; this may have impacted the magnitude and duration of improvements reported in the study. The major findings of this study included:

i.     FMT improves GI symptoms with a 35% decrease in Gastrointestinal Symptoms Rating Scale scores and improvements in stool type (Bristol stool chart and Daily Stool Record or DSR)

ii.     ASD symptoms showed improvements with a 6% decrease in Childhood Autism Rating Scale scores without inducing any severe complications.

iii.     FMT significantly changed the serum levels of neurotransmitters, including changes in serotonin, GABA and dopamine.

iv     They also observed that FMT could promote the colonization of donor microbes and shift the bacterial community of children with ASD toward that of TD children.

In summary, there is growing clinical interest in demonstrating positive clinical benefits and treatment outcomes through FMT for children with autism (ASD) who suffer from chronic GI problems and debilitating symptoms associated with ASD. Completed studies have demonstrated significant improvements in GI and autism symptoms, and more studies are currently underway.

At Novel Biome, we believe in the importance of the gut microbiome for overall health and the possibilities of fecal microbiota transplantation (FMT) to restore gut health and treat disease. Novel Biome focuses on FMT product manufacturing and supplying high-quality products, relying on our world-class donors to allow us to make a significant difference in the lives of many individuals, take our eligibility quiz to see if you can be a stool donor.


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