In my previous articles, I discussed the limitations of genetics in explaining autism and the importance of environmental factors—particularly pesticides during pregnancy. I then addressed the complex issue of epigenetics—the environmental regulation of gene activation or inactivation—an essential process that does not involve changes to the DNA sequence. This is a “non-sequential” form of control, according to the definition provided by my colleague and friend Professor Etienne Danchin, whose book on this subject comes highly recommended (see appendix). In fact, there are hundreds of factors that impact brain maturation and maternal health, often resulting in autism spectrum disorder or other neurodevelopmental disorders. Here, I’ll briefly discuss the microbiome.
The story begins with a researcher who has an autistic child (Dr. Ellen Bolte). She wondered whether her child might have microbiota issues; it should be noted that autistic children often have digestive problems. Consequently, she tried an antibiotic (vancomycin, which targets Clostridium), which had an effect for a few weeks, but then everything returned to the way it was before. Since then, numerous studies have tested probiotic supplements, often with success. Better yet, techniques for transplanting healthy microbiota into rodents and humans have been tested with positive results. For example, transplanting microbiota from an autistic patient into mice (germ-free, lacking microbiota) induces an “autistic” syndrome. Similarly, transplanting the microbiota from a neurotypical person to an autistic individual alleviates the latter’s symptoms.
Given that the microbiota is composed of billions of different bacterial strains, researchers are moving toward identifying particularly harmful strains. Despite its successes, this approach suffers from two major drawbacks:
- The heterogeneity of the syndromes and the bacteria involved makes it difficult, if not improbable, to identify a single universal factor. Research into these factors will likely need to be personalized, making it difficult to apply this approach in a general and universal context;
- It is highly unlikely that pharmaceutical companies will invest millions to validate tests that are ultimately not very profitable, making it difficult to implement this approach on a large scale. Indeed, pilot studies not based on large cohorts and a randomized, double-blind Phase 3 trial will not receive regulatory approval.
Nevertheless, this factor, along with many others, explains both the difficulty of treating autism and challenges the genetic determinism that has been in vogue for decades. Increased monitoring of mothers and infants during the first few months remains the most coherent approach.
