With the number of children diagnosed with autism on the rise, the need to find what causes the disorder becomes more urgent every day. Researchers are now a step closer to showing the link between the food pregnant women consume and the effects on a fetus' developing brain.
Researchers have identified the molecular changes that happen when neural stem cells are exposed to high levels of an acid commonly found in processed foods. In a study published in Scientific Reports, the scientists discovered how high levels of Propionic Acid (PPA), used to increase the shelf life of packaged foods and inhibit mold in commercially processed cheese and bread, reduce the development of neurons in fetal brains.
They began the study after reports showed that autistic children often suffer from gastric issues such as irritable bowel syndrome and wondered about a possible link between the gut and the brain and began examining how the microbiome -- or gut bacteria -- differed between people with autism and those who do not have the condition.
"Studies have shown a higher level of PPA in stool samples from children with autism and the gut microbiome in autistic children is different," the author said. "I wanted to know what the underlying cause was."
In the lab, the scientists found exposing neural stem cells to excessive PPA damages brain cells in several ways. First, the acid disrupts the natural balance between brain cells by reducing the number of neurons and over-producing glial cells. While glial cells help develop and protect neuron function, too many glia cells disturb connectivity between neurons. They also cause inflammation, which has been noted in the brains of autistic children.
Excessive amounts of the acid also shorten and damage pathways that neurons use to communicate with the rest of the body. The combination of reduced neurons and damaged pathways impede the brain's ability to communicate, resulting in behaviors that are often found in children with autism, including repetitive behavior, mobility issues and inability to interact with others.
Previous studies have proposed links between autism and environmental and genetic factors, but the current study is the first to discover the molecular link between elevated levels of PPA, proliferation of glial cells, disturbed neural circuitry and autism.
PPA occurs naturally in the gut and a mother's microbiome changes during pregnancy and can cause increases in the acid. But the authors said eating packaged foods containing the acid can further increase PPA in the woman's gut, which then crosses to the fetus.
More research needs to be done before drawing clinical conclusions. Next, the research team will attempt to validate its findings in mice models by seeing if a high PPA maternal diet causes autism in mice genetically predisposed to the condition. There is no cure for autism, which affects about 1 in 59 children, but the scientists hope their findings will advance studies for ways to prevent the disorder.
"This research is only the first step towards better understanding of Autism Spectrum Disorder," the scientists concluded. "But we have confidence we are on the right track to finally uncovering autism etiology."
A chemical in the processed food linked to autism
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