Autism correlates with an altered gut microbiome
Autism spectrum disorder (ASD) is a neurological and developmental disorder that, among others, affects the way an individual relates to his or her environment. In this disorder both, genetic and environmental factors play a role. In most ASD patients gastrointestinal symptoms such as diarrhea, constipation or flatulence are accompanying illnesses. This connection strongly suggests that there is a correlation between the gut microbiome and ASD. The influence of the gut microbiome to the nervous system might occur via the gut-brain axis. Increasing evidence shows that microbiotic toxins, originating from a disturbed gut microbiome, influence the neuroendocrine, neuroimmune and the autonomic nervous system.
There is an increased permeability of the intestinal tract in ASD individuals
A fundamental fact which supports the evidence of the guts influence on ASD, is the increased permeability of the intestinal tract in ASD individuals, referred to as “leaky gut”. Furthermore the blood-brain barrier is impaired in ASD individuals, facilitating the entrance of bacterial metabolites and toxins into the nervous system.
As shown for other disorders which are correlated with a dysbiosis (disturbance) of the gut microbiome (see also: Impacts of a damage to the microbiome), ASD also seems to occur more likely in children with a disturbed microbiome. Environmental factors like maternal obesity in pregnancy, cesarean birth, formula-feeding, antibiotic administration during pregnancy and in the first three years of life most likely increase the risk of ASD. Children with ASD in average use significantly more antibiotics in early life , thus early life events that can improve a natural development of the children's gut microbiome may prevent the need for antibiotics later on.
The alterations in the bacterial microbiota in the gut of ASD individuals seems to promote the growth of yeasts (Candida) which release ammonia and toxins that can induce autistic behavior. A healthy microbiome would prevent the proliferation of Candida.
The modulation of the gut microbiota is a potential therapy
So far there is no therapy available for ASD, rather parents receive intervention that is tailored to the specific needs of ASD children. All evidences so far indicate that a modulation of the gut microbiota is a potential therapy for ASD patients. Probiotics, prebiotics, fecal microbiota transplantation (FMT) and different diets would be considerable options.
Treatments with probiotics with for example Lactobacilli or Bifidobacteria have shown an enhancement of the intestinal barrier in several studies in human and mice. However, microbiome treatments still lack multicenter, large-sample, randomized controlled trials which are necessary to rule out any possible side effects, especially in ASD children.