What causes Autism Spectrum Disorders (ASD)? The question has puzzled the scientific community for decades. While the gut cannot fully explain the causes of ASD (characterized by difficulties in socializing and communicating, or even obsessive-compulsive disorders (OCD)), it may provide some of the answers. These answers are to be found in the billions of bacteria and other microorganisms that populate the gut microbiota, for better or worse.
Gut disorders and ASD: a dangerous liaison
Since ASD was first described in 1943, numerous symptoms have been identified. Gut disorders (diarrhea, constipation, irritable bowel, etc.) are among the most standard physical symptoms. Children with ASD experience three to four times more gastrointestinal disturbances than the norm. Severe autism often goes hand in hand with the most severe gut disorders–and vice versa. In fact, researchers have even shown that autistic patients show an improvement in behavior following treatment of a gastrointestinal disorder. They therefore became interested in the mechanisms behind these gastrointestinal disorders and took a closer look at the gut microbiota.
A microbiota that believes itself to be the brain
Observation no. 1: autistic patients often present an altered gut flora (dysbiosis) that is poor in beneficial bacteria and richer in microbes involved in certain gut disorders (diarrhea, constipation, etc.). Not content with troubling the gut, these microbes also produce “signal” molecules used by the gut and the brain to communicate. Produced to excess, these molecules could interfere with the communication process and lead to behavioral disorders such as those encountered in ASD.
A leaky gut?
Observation no. 2: the gut barrier no longer does its job, i.e., preventing microbes, allergens and other foreign molecules from entering the bloodstream. The immune system is activated as a result, triggering inflammatory reactions. Many autistic patients exhibit gut permeability, gut and neuronal inflammation and gut disorders associated with a response to heightened stress. These data suggest a strong gut-brain link in ASD. However, the mechanisms by which gastrointestinal disorders contribute to autism are extremely complex. Further research is therefore required to identify therapies to treat these gut problems and improve the quality of life of patients with ASD.
