July 17, 2019

A new review demonstrates the role of the gut microbiome in autism spectrum disorders

Autism Spectrum Disorder (ASD) has an unclear cause but is associated with various genetic, neurologic, metabolic, and immunologic factors. Although there is no definitive treatment, gastrointestinal symptoms are common in patients with autism. Patients with ASD who present GI symptoms may show significant behavioral manifestations, such as anxiety, self-injury and aggression. 

According to a recent review in Frontiers in Cellular Neuroscience, researchers review the bidirectional interactions between the central nervous system (CNS) and the gastrointestinal tract vita the brain-gut axis and the role of the gut microbiota in the CNS and ASD.

A review of over 150 papers on ASD and gut bacteria found that since the 1960s, researchers have been reporting the association between the composition of gut microbiome and autistic behavior. This review highlights many studies showing that restoring a healthy balance in gut bacteria can treat ASD symptoms.

Research demonstrates that the gut microbiota is directly or indirectly associated with ASD symptoms altering the immune system and metabolism. Studies show a higher percentage of intestinal permeability in ASD patients resulting in a higher antigenic load from the gastrointestinal tract. These inflammatory cytokines are present in the circulation and cross the blood-brain barrier (BBB). Alterations in the composition of the gut microbiota and their metabolic products are commonly observed in patients with ASD. For example, lipopolysaccharide (LPS) is increased in the serum of ASD patients and is associated with impaired social behavioral scores.

In addition, the gut microbiome of children with ASD is less diverse with lower levels of Bifidobacterium and Firmicutes and higher levels of Lactobacillus, Clostridium, Bacteroidetes, Desulfovibrio, Caloramator and Sarcina. Also, children with autism who present gastrointestinal symptoms have lower abundances of the genera Prevotella, Coprococcus, and Veillonellaceae and higher levels of the Clostridium histolyticum. The reduction of Clostridium results in significant improvements with ASD symptoms.

Researchers also found that Candida was twice as abundant in ASD. The dysbiosis seen in ASD results in the expansion of Candida leading to further imbalance and an exacerbation in abnormal behaviors.

Early life events can alter the composition of the gut microbiome in ASD patients. These may include the overuse of antibiotics, maternal obesity and diabetes during pregnancy, how a baby is delivered, and if and how long the infant was breastfed.  Keep in mind in a child under 3 years of age whose brain is at the height of development may have impaired neurodevelopment due to the presence of the metabolic products resulting from the dysbiosis and intestinal permeability.

At present, there are no effective therapies for ASD. Many of these children take nutritional supplements and follow specific diets such as a gluten-free and casein-free (GFCF) diet.

It is essential to assess gut health in patients with ASD. Many of these children have a dysbiosis and opportunistic infections.

Children with ASD have significantly different concentrations of certain bacteria in their stool compared to children without ASD. Increasing evidence suggests that children with ASD have altered gut bacteria. It is suspected that gut microbes can alter the levels of neurotransmitter-related metabolites affecting the gut-to-brain communication and alter brain function.

By Michael Jurgelewicz, DC, DACBN, DCBCN, CNS

Source:  Qinrui Li, Ying Han, Angel Belle C. Dy, Randi J. Hagerman. The Gut Microbiota and Autism Spectrum Disorders. Frontiers in Cellular Neuroscience, 2017; 11 DOI: 10.3389/fncel.2017.00120

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