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Autism could start in the digestive system rather than the brain.
A recent research reveals that autistic children exhibit notably distinct bacterial composition in their stomachs when contrasted with those who do not have this condition.
According to the researchers, these alterations in the microbiome — which is a system of bacteria responsible for regulating digestion and various other functions — result in modifications in certain areas of the brain linked to behavior and learning.
Nutrition and various environmental factors during pregnancy have been associated with detrimental alterations in the baby’s microbiome.
The team observed that autistic children were more prone to having mothers who took antibiotics during their pregnancy, indicating that the medication usage might have heightened the risk of autism.
They examined stool samples and brain scan results from children between eight and 17 years old who had autism, comparing them to those of typically developing children within the same age range.
The researchers discovered that autistic children and teenagers exhibited reduced amounts of specific metabolites—small substances formed during digestion—compared to those who were not on the autism spectrum. This reduction led to decreased production of serotonin, a hormone crucial for regulating mood, within their digestive systems.
The researchers believe these alterations in the intestinal microflora may lead to symptoms of autism such as challenges with communication and behavioural problems.
For many years, this notion of a 'gut-brain' link has been proposed as a possible factor contributing to autism, yet it has remained believed to have been disproven .
Nevertheless, the recent research revives that theory by examining both stool samples and brain scans simultaneously, focusing particularly on specific groups of metabolites.
The team, from the University of Southern California, said the findings could lead to treatments targeting the gut 'while also hopefully alleviating some of the symptoms that are the most uncomfortable for [autistic children],' like bloating and constipation.
Nevertheless, they warned that further extensive, conclusive studies are required.
Lisa Aziz-Zadeh, who led the study and is a professor at the Brain and Creativity Institute at the University of Southern California, California , stated: "Our findings show that substances produced in the gut influence the brain, which then influences behavior. Fundamentally, the brain serves as a mediator linking gut condition with autism-associated actions."
'Studies before us have pointed out variations in gut microbiomes and brain structures among people with autism, yet our work ties these pieces together.'
The discoveries coincide with one out of every 36 children in the US being diagnosed with autism, totaling nearly 2 million individuals. Back in the early 2000s, this ratio was approximately one in 142, indicating a significant increase of about four times.
Specialists are striving to reveal the reasons behind the rise. expressing worries about ecological elements like microplastics and pesticides.
They've also observed that improved diagnostics have made it simpler for physicians to identify the condition, particularly among previously neglected demographics such as girls and adults.
The research, released on Monday in Nature Communications , compared 43 children with autism to 41 neurotypical children from health facilities in Los Angeles .
Each participant was aged from eight to 17 years, with an average age of 12.
Approximately fifty percent of the autistic participants were taking medication such as antidepressants, antipsychotics, and stimulants to manage their behaviours. No neurotypical children used prescribed drugs.
The researchers instructed all the children to refrain from using antibiotics for one month and avoid probiotics for two weeks, since these substances can affect the balance of microbes in their intestines.
The research was conducted across two days. During the initial day, the team administered behavioral evaluations to the kids. The following day, the subjects provided fecal samples and went through brain MRI scans.
Parents were additionally requested to indicate which dietary pattern their children adhered to most closely: Standard American (characterized by high intake of processed items, red meats, poultry, eggs, and dairy products); Modified American (marked by higher amounts of whole grains, poultry, fish, eggs, dairy, veggies, fruits, along with certain processed foodstuffs); Mediterranean; Paleo; vegetarian; gluten-free; dairy-free; low FODMAP; or another specific regimen.
The researchers focused on metabolites in the participants' stools that were part of the 'tryptophan pathway.'
Tryptophan is an amino acid present in foods such as turkey, salmon, eggs, and seeds; this substance converts into the metabolite serotonin, essential for various brain activities including emotion regulation, social behavior, and cognitive processes.
The researchers noted because more than 90 percent of the body's serotonin is produced in the gut, changes in gut health could influence serotonin levels.
The nerve cells within the gut subsequently transmit messages to the brain, a process referred to as the gut-brain axis.
The team discovered that children with autism exhibited reduced amounts of tryptophan metabolites compared to neurotypical children, leading to decreased serotonin levels.
This resulted in increased rates of digestive problems such as bloating and constipation along with a higher occurrence of alterations in parts of the brain linked to social interactions, resulting in symptoms associated with ASD.
Aziz-Zadeh stated: "It is known that children with autism exhibit brain differences — specific regions of their brains show lower activity or higher activity when contrasted with neurotypical children."
'We also understand that they frequently face gastrointestinal challenges like constipation, abdominal pain, and other digestion-related issues. Moreover, autism comes with several symptoms, which include repetitive actions and struggles with social interactions.'
In addition to dietary factors, reduced levels of tryptophan metabolites might also result from antibiotics disrupting the gut microbiome. The researchers discovered that children with autism were more likely to have had mothers who used antibiotics during pregnancy.
The researchers stated: "Exposure to antibiotics before birth can influence the mother's microbiome, impacting the fetus' brain through modified microbial substances produced by the mother."
This prenatal process has been suggested to contribute to the development of ASD.
Nonetheless, the researchers warned that "our study cannot establish causality," implying that it doesn't directly prove that metabolite levels lead to autism.
Advocacy organisations for autism have stated that the reasons behind autism are not completely clear, and numerous specialists indicate that there isn’t just one particular cause.
The research had multiple constraints, such as excluding children younger than eight years and featuring an unequal gender ratio with more males involved.
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