Autism and the Gut Microbiome

As explained in our last post Autism and Gut Microbiome, Autism spectrum disorder (ASD) is a complex neurodevelopmental condition that affects communication, behavior, and social interaction and is often associated with repetitive and restrictive behaviors. While the exact causes of autism remain elusive, research in recent years has increasingly focused on the gut-brain connection and the role of dysbiosis in autism. Dysbiosis refers to an imbalance or alteration in the gut microbiome – the vast community of microorganisms residing in our digestive tract. Emerging evidence suggests that dysbiosis may play a significant role in the development and severity of autism symptoms.

Gut Bacteria and Autism

Several studies have shown that autistic people exhibit dysbiosis compared to neurotypical or healthy people. The dysbiosis state can manifest as an overgrowth of harmful bacteria, a reduction in beneficial microbes, or alterations in microbial diversity (the richness and evenness of microbial species). Studies have reported an overgrowth of harmful gram-negative bacteria such as Desulfovibrio (resistant to several antibiotics) and Bacteroides vulgatus in autistic children compared to healthy controls. Many of these gram-negative bacteria contain lipopolysaccharides (LPS) in their cells which has damaging effects on tissues including the brain. Inflammation induced by these LPS increases the permeability of the blood-brain barrier which encourages the migration and accumulation of pathogenic microbes and their toxins in the brain aggravating the symptoms observed in ASD.

In addition to the gram-negative species, studies have also shown that the abundance of the gram-positive Clostridium is higher in autistic children than in healthy controls. This gram-positive bacterium has been widely studied in the context of ASD. The rationale for its implication in ASD is mainly because Clostridium species such as Clostridium difficile are known to produce exotoxins and propionate which worsens ASD symptoms as well as p-cresol which has been shown to deplete glutathione – an antioxidant that detoxifies heavy metal such as mercury and lead in the blood. In fact, some studies have correlated an increased level of brain auto-antibodies with higher amounts of mercury in the serum of autistic children compared to their non-autistic counterparts. The depletion of glutathione increases vulnerability to ASD and other neurodevelopmental disorders. Autistic children have been shown to harbor several species of Clostridium (C.scindens, C.nexile, and C.orbiscindens amongst others) not found in healthy controls.

Similarly, studies have reported a reduction of beneficial bacteria in autistic children compared to healthy children. For instance, studies have shown that the abundance of the genus Bifidobacterium which has anti-inflammatory properties is reduced in autistic children compared to healthy controls. Additionally, studies have shown that the abundance of important carbohydrate-degrading or fermenting bacteria such as Prevotella, Coprococcus, and Veillonellaceae are reduced in autistic children. Microbial species such as Prevotella are important in the digestion of various complex carbohydrates found in foods and in the biosynthesis of vitamins. This could be important for therapeutic interventions because autistic children have been reported to have impaired carbohydrate metabolism (malabsorption and maldigestion problems). Finally, studies have shown that the microbiota of autistic children is characterized by a less diverse microbiota comprised of a lower abundance of microbial groups which mainly includes beneficial gram-positive species such as Prevotella, Coprococcus, Bifidobacterium and Veillonellaceae. A higher microbiota diversity is usually associated with a healthier and better health outcome.

Signs of Autism in Toddlers

Some children exhibit noticeable signs within their first few months, while others may not display signs until later.

Signs of Autism in Infants (Up to 12 Months)

During the first year of life, some potential indicators of autism may include:

• Minimal or absent babbling
• Limited eye contact or avoidance
• Showing greater interest in objects than in people
• Not responding to their name or spoken cues
• Unusual ways of engaging with toys, such as repetitive actions
• Repetitive finger, hand, arm, or head movements
• Initial development of language skills followed by regression or loss of those skills

Signs of Autism in Toddlers (Up to 2 Years)

As toddlers grow, additional signs may become apparent, such as:

• Highly focused interests in specific topics or objects
• Little to no interest in engaging with other children
• Behavioral challenges, including self-isolation or self-harm
• Repetitive use of words or phrases without understanding their meaning
• Difficulty engaging in interactive play, like peek-a-boo
• Preference for strict routines, such as eating the same food consistently

Individuals on the autism spectrum, regardless of age, may exhibit various signs that affect their social interactions, communication, and behavior. They might have reduced eye contact and show strong reactions to sensory stimuli such as lights, sounds, tastes, smells, colors, or textures. Many develop highly specific and intense interests, often focusing deeply on particular topics or activities. Repetitive behaviors, such as spinning or persistently repeating words and phrases, are also common. Some individuals experience delays in language development or rely on nonverbal communication. Additionally, even minor changes in routine or environment can cause significant distress, highlighting their need for predictability and consistency in daily life.

The Connection Between Autism and the Gut Microbiome and Exploring Interventions for Autism

The growing body of evidence linking dysbiosis to autism opens exciting possibilities for novel treatments and interventions. While research is still in its early stages, some promising avenues include the use of prebiotics and probiotics (beneficial bacteria and dietary fibers), dietary modifications and fecal microbiota transplant (FMT) which involves transferring healthy donor stool to a recipient's gut to restore microbial balance. While FMT is a potential treatment avenue, it is still in the experimental stage for autism.

In summary, dysbiosis in autism is a fascinating and evolving area of research that highlights the intricate connection between the gut and the brain. While we are still unraveling the exact mechanisms and therapeutic potential, it offers hope for new interventions to improve the lives of individuals with autism. As our understanding of the gut-brain axis deepens, it is increasingly clear that nurturing a healthy gut microbiome may be a key component in the holistic approach to managing autism spectrum disorder.