Up to 90% of people with autism, which is characterized by “impaired social communication and repetitive and stereotyped behavior, interests, or activities’ (Zhang et. al, 2020), have issues with their gut. New studies are uncovering a link between autism and gut microbiome dysfunction. Many patients with autism are picky eaters and have low levels of digestive enzymes, which can lead to inflammation in the intestinal epithelium, and ultimately leaky gut. When the body’s microbial detox abilities are impaired it creates a heavy overall toxic burden. As inflammation causes a less effective epithelium, leaky gut worsens and more toxins seep into the blood. The toxic burden grows and the body’s ability to detox is further hindered. Toxins that are released into the bloodstream travel through the body, where they damage organ tissues and structures, specifically mitochondria. Damaged mitochondria may release molecular patterns that indicate damage has occurred. These patterns can result in inflammatory responses in many organ tissues,  including the brain. This process may be involved in the pathology of autism.

Gut bacteria can generally be classified as good bacteria or bad bacteria. However, the gut is much more complex than this simple picture. Each individual needs a unique combination of bacteria to function effectively. Individuality complicates the process of determining how the microbiome affects diseases. Simply put, if everyone needed the same amount of each strain of bacteria it would be easy to spot the differences between healthy individuals and those with autism. One study focused exclusively on comparisons between the gut bacteria of healthy children and children with autism. They found that the diversity and richness of the microbiome was indistinguishable between the two groups. However, they did find a number of bacteria strains and enzymes that were significantly elevated or deficient in autistic children. Five detoxification pathways had deficient function in ausistic children. These pathways involved the degradation of organic toxins, such as those found in food additives, insecticides, automotive exhaust, and heavy metals. Most organic toxicants are lipid soluble and thus tend to accumulate in fatty areas of the body including the brain (Zhang et. al, 2020), where they can cause damage to the membrane structures. Deficient detoxification pathways lead to further toxic buildup. Researchers also learned that the degradation pathway of methylglyoxal, a compound that’s build up has been linked to multiple degenerative processes, including brain lesions  (Zhang et. al, 2020), was deficient. 

 One recent study collected fecal matter from healthy subjects and transferred it into people with autism. Surprisingly, after autisitc individuals received the transplants, the behavioral and psychological symptoms of autism improved (Haridy, 2019). Another study worked with human fecal matter and mice. Researchers took fecal matter from humans with autism and from those without autism. When samples from humans without autism were placed inside the mice, no symptoms were observed. However, the story was different when samples from autistic individuals were placed inside the mice. The infected mice started displaying classic symptoms of autism; such as, decreased social interaction, and increased repetitive actions (Haridy, 2020). . Another interesting finding of this study was that mice which had received the fecal implants from autistic humans had differences in gene expression within their brains. They also had different levels of two key metabolites in their body. When researchers performed supplementation of those metabolites, the symptoms of autism improved in mice. This study does not mean that gut bacteria alone causes autism; rather, that the microbiome interacts with other body systems and deficiency in detoxification pathways can increase the severity of autism like behaviors. Researchers were able to find similar results in humans. By simply analysing the microbiome they were able to predict, with 88% accuracy if the child had autism  (Zhang et. al, 2020). These studies are a while away from creating accepted treatment for autistic individuals, but they do raise an interesting line of question for further research. 

Haridy, Rich. “New Evidence Links Gut Bacteria Alterations to Autism.” New Atlas, 26 Oct. 2020, newatlas.com/science/gut-bacteria-microbiome-asd-autism-metabolic-detoxification/. 

Haridy, Rich. “Two New Studies Strengthen the Gut-Brain Connection in Autism.” New Atlas, 31 May 2019, newatlas.com/autism-gut-microbiome-gene-fecal-transplant/59931/?itm_source=newatlas. 

Zhang, Mengxiang, et al. “A Quasi-Paired Cohort Strategy Reveals the Impaired Detoxifying Function of Microbes in the Gut of Autistic Children.” Science Advances, vol. 6, no. 43, 2020, doi:10.1126/sciadv.aba3760.