A Korean-American couple may have found one of the causes of Autism spectrum disorder (ASD), a condition that has puzzled scientists from all over the world since it was first described in the 1940s.
Harvard Medical School faculty member and former assistant professor at UMass Medical School, Jun-ryeol Huh, and his wife, Gloria Choi, an assistant professor of brain and cognitive sciences at MIT, claim to have identified not only what causes the disorder that can affect how the brain develops, but also potential techniques to preventing and reversing the disorder’s effects through their experiments and observations of mice.
In two research studies published by the science journal “Nature” (via MIT news) on September 14, 2017, the pair of professors reported that they discovered certain strains of bacteria in the mother’s digestive tract that may lead to behaviors resembling autism in their offspring such as repetitive behavior and impaired sociability.
In a related function, mothers who experience severe infections that require hospitalization during their pregnancy face a higher risk of giving birth to a child with autism. A 2010 study involving observations of children in Denmark listed these types of infections as influenza, viral gastroenteritis, and severe urinary tract infections.
Choi, a member of MIT’s McGovern Institute for Brain Research, explained that they identified specific regions of the brain responsible for the behaviors seen in autism:
“We identified a very discrete brain region that seems to be modulating all the behaviors associated with this particular model of neurodevelopmental disorder.”
In a 2016 study published in “Science”, Choi and Huh learned that the regions of the brain responsible for influencing autistic behaviors were afflicted by what they called “patches.”
These patches were caused by the effector molecule (IL-17) of a particular type of immune cell (Th17 cells) that are released due to inflammation in the mother’s body as it fights off an infection. The effector molecule interacts with receptors in the brain of the fetus causing the irregularities called patches.
The patches are located in a specific part of the brain known as S1DZ, part of the somatosensory cortex which is a region thought to control proprioception, or being able to sense where the body is in space.
Within this patches in S1DZ are cells called interneurons that produce a protein (parvalbumin) and are responsible for balancing inhibitions and excitation. In the mice, interneuron counts in the patches were reduced, leading to what researchers described as an overexcitment of S1DZ.
When researchers restored balance in the region of the brain, the autistic behaviors were reversed. In normal mice, researchers overstimulated neurons in the region and recreated the autistic behaviors.
In the second “Nature” study, researchers looked at more factors to explain why not all mothers who experience infection end up having autistic children. Cho stated:
“This suggests that inflammation during pregnancy is just one of the factors. It needs to work with additional factors to lead all the way to that outcome.”
Looking at the role the effector molecules of the immune cells from the mother affected the fetus, researchers determined that one specific type of harmless bacteria in the fetus, known as segmented filamentous bacteria, signaled the development of patches in the brain and behavioral abnormalities.
When researchers eliminated this strain of bacteria with antibiotics, the mice produced offspring with normalized behaviors.
“This data strongly suggests that perhaps certain mothers who happen to carry these types of Th17 cell-inducing bacteria in their gut may be susceptible to this inflammation-induced condition,” said Huh.
Researchers now plan to investigate whether these kinds of bacteria have the same effect on the immune cells Th17 in humans, potentially leading to the development of autism in newborns.
This also sparks debate on preventative measures for autism, like blocking certain strains of bacteria from causing this immune response in the mother’s gut.