Updated on December 22, 2022
- Gastrointestinal symptoms are common among autism patients, and there is compelling evidence these symptoms require unique interventions based on the gut microbiome divergencies associated with autism.
- Researchers have found that the microbiomes of autism patients tend to have significantly different bacterial population sizes and proportions than the microbiomes of healthy patients, which might explain the prevalence of gastrointestinal distress and contribute to other symptoms of autism.
- Based on these findings, many in the scientific community suggest it might be possible to address a range of autism symptoms by improving the health of the gut microbiome via targeted therapies, such as short-chain fatty acid supplementation.
Clinical care of autism patients is challenging, with a diverse set of comorbidities complicating the management of core deficits. Autism is defined primarily as a neuro-developmental issue characterized by impaired communication, limited social engagement, and repetitive behaviors. However, an array of other symptoms often accompany these core traits. In particular, gastrointestinal problems appear to be common comorbidities for individuals with an autism spectrum disorder. Research indicates that gastrointestinal symptoms occur in children with autism at rates 3-4 times higher than seen in those without. Communication deficits that are the hallmark of autism spectrum disorder can confound diagnosis and delay treatment of gastrointestinal distress. In some children, abdominal symptoms can present as a persistent cough, recurrent throat clearing, or an exacerbation of problem behaviors, such as self harm.
Although there appears to be a consensus on an association between autism and gastrointestinal problems, a definitive link between the two remains elusive. Without clear evidence of a causative underlying pathology, health-care professionals apply the same standard of care for patients with and without autism to address gastrointestinal complaints. This standard typically focuses on symptom management. However, in addition to gastrointestinal problems, research shows that individuals with an autism spectrum disorder tend to have a contentious relationship with food in general. For many on the autistic spectrum, food allergies, decreased bowel motility, and self-avoidance of certain foods disrupt their nutritional intake.
Some researchers are now exploring the gut microbiome and the bioactive compounds that certain bacteria produce through fermentation in the intestine. Their work seeks to elucidate the association between autism and gastrointestinal problems. The gut microbiome is the complex and diverse population of microorganisms that inhabit the human gut and exist in a mutualistic relationship with its host. Although this relationship is integral to the health of the gastrointestinal tract, it also extends beyond the gut because the gut microbiome interacts with every system in the body through neurologic, immunologic, and endocrine mediators. While our understanding of this complex network is far from complete, each new piece of evidence is bringing us closer to therapeutic modalities that leverage this relationship.
The Gut Microbiome – The Forgotten Organ
As a species, humans have coevolved with the gut flora that resides within us. Our physiology is intimately intertwined with the hundreds of different bacteria, viruses, and fungi that call our guts home. Digestion is one of the most basic and influential metabolic processes of human health where this microbiome is involved. Of particular importance is a group of bacteria known as the fermenters. Humans lack the enzyme that breaks down large carbohydrate molecules. Through the metabolic process of fermentation, these large carbohydrate molecules are converted to smaller molecules, like short-chain fatty acids, that can then be absorbed. The fiber in our diet—such as that found in fruits, vegetables, legumes, and unrefined grains—is indigestible. However, after it is in the large intestine, this fiber undergoes fermentation by the microorganisms found there. This fermentation not only metabolizes these non-digestible carbohydrates into nutrients that support the microbiome, but the products of this metabolism—short-chain fatty acids like butyrate, propionate, and acetate—become bioavailable to the host. Not only are short-chain fatty acids vital for the health of the lining of the gut, they also act as mediators of inflammation in the gut and can even cross the blood-brain barrier to affect neurotransmitters in the central nervous system. Manipulating one’s diet to increase short-chain fatty acids in the gut has been shown to decrease pro-inflammatory markers, benefit gut motility, and increase serotonin levels, reminding us that the interaction of the gut microbiome and the food we eat influences nearly every aspect of a person’s health.
Autism and the Dysfunctional Gut
Although many medical professionals agree there is a correlation between autism and gastrointestinal dysfunction, there are few definitive answers to the pathophysiology behind it. However, studies examining the gut microbiome in individuals with autism do provide interesting clues.
Numerous researchers have demonstrated differences in the microbiome of individuals with autism compared to standard control groups. One of these studies noted significantly reduced populations of Prevotella, Coprococcus, and Veillonellaceae species, all of which ferment carbohydrates in the intestine to produce short-chain fatty acids. Prevotella species functions in two important ways: it possesses the genes for the biosynthesis of vitamin B1 and high populations of Prevotella correspond to low populations of Enterobacteriaceae, such as Salmonella and Shigella, suggesting a protective effect against pathogenic bacteria. This study, in addition to finding reduced populations of fermenting bacteria, also noted that the microbiome is less populated and has a decrease in the diversity of populations of microbes in the gut of individuals with autism, with the least diversity correlating with more severe gastrointestinal problems.
With data suggesting a link between the gut flora’s production of short-chain fatty acids and gastrointestinal disturbances, some researchers are now exploring the possibilities of manipulating the microbiome to ameliorate symptoms. For example, probiotics, like Lactobacillus, have been shown to reduce abdominal symptoms in conditions like inflammatory bowel disease, and Saccharomyces is showing promise as an adjunctive treatment for diarrhea in children with autism. As scientists gain greater insight into the connection between symptoms associated with autism and the composition of their microbiome, both clinicians and caregivers can gain increased awareness of how to work with these microbes to alleviate gastrointestinal problems in the autistic patient or perhaps even prevent them from occurring.
The Promise of New Treatments
As we continue to explore the gut microbiome, to reacquaint ourselves with this “forgotten organ,” we are finding potential new avenues of treatment for myriad ailments. To the millions who suffer with gastrointestinal problems, research of the microbiome is inspiring several novel therapeutic strategies to alleviate their distress. For those who suffer from autism, working with the microbes in the gut might be doubly beneficial, with some data suggesting psychiatric and neurologic benefits in addition to improvement of gastrointestinal symptoms. Whether it is dietary modification, pre- and probiotic supplements, or the administration of short-chain fatty acids like butyrate, considering the role of the microbiome in gastrointestinal health provides clinicians with a new approach, one that works with the mutualistic interaction between microbiome and host.
The growing body of knowledge about the gut microbiome, even in just the last few years, demonstrates immense potential in co-opting biochemical mechanisms to treat and prevent disease. Pharmaceutical companies are currently exploring bioavailable molecules that are products of bacterial fermentation in the gut as the basis for new and safer drugs, and cutting-edge nutritional supplements targeted toward stabilizing the gut microbiome are already on the market. Better comprehension of the role the microbiome plays in early development might also inspire methods of supporting these organisms in children as a preventative measure against future developmental dysfunction. For those already living with autism, the medical community is actively investigating these microorganisms and their role as mediators of health and disease, and each new discovery guides refinements to their methods.
As our understanding of the gut microbiome grows and informs the development of more advanced therapeutics, the future of medicine opens innumerable possibilities for potential treatments.
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