Two years ago, 18 children underwent an experimental fecal transplant to relieve symptoms associated with autism spectrum disorder (ASD). Today, they are continuing to show signs of improvement.  

In a follow-up study published in Scientific Reports, researchers report a 45 percent reduction in ASD symptoms and a 58 percent decline in gastrointestinal symptoms compared to pre-treatment.

"We are finding a very strong connection between the microbes that live in our intestines and signals that travel to the brain," Rosa Krajmalnik-Brown, a professor at the Biodesign Institute at Arizona State University (ASU) and study co-author, said in a statement.

"Two years later, the children are doing even better, which is amazing."

While it might seem counterintuitive to associate a neurodevelopmental disorder with bacteria in the gut, a spate of recent studies has shown just how connected our microbiome (our unique blend of gut bacteria) is to our health and behavior more generally – whether it's our propensity for depression or our sociability.

Hence, medical interest in fecal transplants, a method for gifting a more diverse set of bacteria to those with more limited gut microfauna, is increasing. Fecal transplants have been used to tackle anything from cognitive function decline to obesity and superbugs. There's even evidence to suggest it can make you a better professional cyclist. (Yes, really.)

Here, researchers have attempted to alleviate ASD symptoms in 18 children using Microbial Transfer Therapy (MTT) – a method that involves two weeks of antibiotic treatment, a bowel cleanse, and fecal microbiota transplants, starting with a high initial dose and followed by seven to eight weeks of a lower doses to be taken daily. 

Before treatment, the children diagnosed with ASD had a less diverse microbiome than a control group of neurotypical children. Specifically, they were lacking certain strains of "good" bacteria, including Bifidobacteria and Prevotella. But this changed with treatment and continues to be the case two years on. Indeed, microbial diversity appears to be even higher now than it was immediately after the initial study.

"It is very unusual to see steady gradual improvement after the conclusion of any treatment," co-author James Adams, also from ASU, explained.

“We only conducted the long-term follow-up study after several families told us that their child was continuing to improve significantly.”

This has translated to a 45 percent decrease in ASD symptoms compared to a baseline two years ago. Whereas at the start of the experiment, 83 percent of the children were considered to have "severe" ASD, this dropped to 17 percent. Now, 39 percent would be considered "mild" or "moderate" and 44 percent would be below the cut-off for "mild" ASD. 

There was a similarly dramatic decrease (58 percent) in gastrointestinal problems, which affect between 30 and 50 percent of people diagnosed with ASD and all of those involved in the study. Only two (11 percent) achieved a less-than-50-percent reduction.

This is all extremely promising, particularly for people with a severe form of ASD that can interfere with everyday life. But it is certainly not a "cure". Rather, it is the initial stages of a therapy that may be used to relieve some of the symptoms of ASD and the gastrointestinal problems that often coincide.

The researchers are keen to point out that studies so far have involved small sample sizes and lack a placebo, while they are still working out what is the "optimal dose" and whether or not to include booster doses. They are currently involved in a larger placebo-controlled trial in adults.

"[We] are excited about the results, but we want to caution the public that we need larger clinical trials for this to become an FDA-approved treatment,” Adams added.