INTRODUCTION
Today, I’m going to present to you the link between autism and the gut microbiota. Indeed, it is a
complex subject that is constantly evolving.
PRESENTATION OF THE GUT MICROBIOTA
The gut microbiota is an ecosystem of microorganisms that reside in our digestive system.
● It is absent in a fetus during pregnancy.
● From birth until the first three years of life, the gut microbiota develops and diversifies due to
various environmental factors such as diet or human contact.
● By the age of 3, the gut microbiota stabilizes in its final form for life.
However, factors can influence the microbiota like the mode of delivery.
→ It has been shown that cesarean section alters the acquisition of bacterial diversity and that this
alteration could have an impact on the development of diseases such as asthma.
In adulthood, the gut microbiota is continually regulated by external factors such as diet or antibiotic
treatments.
COMPOSITION OF THE GUT MICROBIOTA
The gut microbiota is composed of a wide variety of microorganisms, including bacteria, viruses,
fungi, and archaea. Bacteria constitute the majority of the microbial population present in the digestive
tract.
Among bacteria, several dominant groups are found, such as Firmicutes, Bacteroidetes, and
Proteobacteria.
Each individual has a specific composition of gut microbiota influenced by factors such as age, diet,
lifestyle, or exposure to antibiotics. This microbial diversity plays a crucial role in digestive health.
ROLE OF THE GUT MICROBIOTA
The gut microbiota plays several essential roles in the body.
1. Facilitation of digestion and absorption of nutrients such as sugars and amino acids by
intestinal cells.
2. Maturation of the digestive system through the production of intestinal mucus and enzymatic
activity of the mucosa.
3. Protection against pathogenic bacteria and toxins through antimicrobial molecules.
4. Development of the immune system because gut microbiota bacteria can activate intestinal
immune system cells.
LINK BETWEEN THE GUT AND THE BRAIN
The link between the gut and the brain is referred to as the gut-brain axis or microbiota-gut-brain axis.
This axis represents bidirectional communication between the gut and the central nervous system.
● The brain influences the gut via the autonomic nervous system : it regulates functions such as
intestinal motility and hormone secretion.
● The gut sends signals via neurotransmitters to the brain through various pathways such as
the vagus nerve. These signals can impact behavior.
Disruptions in the balance of the microbiota can be associated with various neurological disorders
such as anxiety, depression, and neurodevelopmental disorders such as autism.
PRESENTATION OF AUTISM
Autism or Autism Spectrum Disorder ( ASD ) is a neurodevelopmental disorder that alters how a person
interacts with others, communicates, perceives the world, or manages emotions.
Autism is characterized by difficulties in social communication, repetitive and restricted behaviors, and
specific interests. It has been observed that individuals with this disorder present significant intestinal
symptoms.
Researchers have therefore explored a potential link between this disorder and the gut microbiota.
LINK BETWEEN AUTISM AND THE GUT MICROBIOTA
Interest in the link between autism and the gut microbiome has recently increased due to high rates of
intestinal symptoms in ASD patients, as well as the growing interest in the gut-brain axis.
Research on the link between gut microbiota and autism is still ongoing and leads to several
hypotheses.
● HYPOTHESIS 1 : Researchers have demonstrated a link between autism and the low presence
of Bacteroides fragilis in the digestive system. Their study was conducted on mice in which they
induced autistic symptoms with chemical agents. However, this study has not shown significant
results so far.
● HYPOTHESIS 2 : Researchers have demonstrated a link between autism and the bacterium
Romboutsia timonensis. The authors examined stool samples to analyze microbial DNA in ASD
patients and undiagnosed subjects. They found that this species is less present in ASD patients
and that this could be related to a reduction in dietary diversity.
POTENTIAL THERAPEUTIC TARGETS
Numerous studies have established a link between gut bacteria and autism. This paves the way for
research aimed at alleviating the symptoms of this disorder.
Among these approaches, microbiota transplantation represents a promising avenue. This method
aims to modify the gut microbiota to reduce symptoms associated with this neurodevelopmental
disorder.
Researchers have undertaken microbiota transplantations in autistic children aged 7 to 16 with intestinal
symptoms. Among the 18 participants, 15 were considered to have severe autism.
The results obtained are encouraging and showing a significant improvement in autistic symptoms
in these children after the transplantation.
However, further investigations are needed to better understand the underlying mechanisms and
evaluate the long-term effectiveness of this approach in the treatment of autism.
CONCLUSION
The link between autism and the gut microbiota opens up new perspectives in the field of health and
research, and this relationship could lead to significant advances in the diagnosis and treatment of
autism.
QUESTIONS :
Do you know if alterations in the gut microbiota are involved in other disorders or pathologies ?
- Parkinson’s disease → link between the abundance of the bacterium Bilophila wadsworthia
and the progression of Parkinson's disease.
- Eating disorders → protein produced by Escherichia coli is a mimic of a hormone,
melanotropin, which regulates satiety.
- Obesity
Besides fecal therapy, are there any other therapies to restore the intestinal microbiota?
Bacteriophage-based therapies : Bacteriophages are viruses that infect and destroy bacteria. They
could target specific imbalances in the intestinal microbiota
