Tired of fake news? A possible cause behind autism spectrum disorder: the gut microbiome.
By Christopher Yoon
THE MYTHS OF AUTISM SPECTRUM DISORDER
Among the current epidemic of pseudoscience, Facebook bandwagons, and anti-vaccines, the mystery of the cause of autism spectrum disorder (ASD) has been in the spotlight for quite some time. The complexity of this disorder and its spectrum of effects makes it incredibly hard to pinpoint the exact mechanisms of the cause, so it would be hypocritical to say that skepticism isn’t warranted.
Although these opinions regarding the cause of ASD have no scientific backing, the amount of research to be done to truly uncover the exact causes are large. Nonetheless, from a logical point of view, the benefit of getting vaccinated — essentially avoiding death, especially to those with autoimmune disorders — clearly outweighs the spectrum of this disorder’s effects, where high-functioning autistic children are not uncommon and often live normal lives (literally).
WE AREN’T EXACTLY RIGHT EITHER
It must be pointed out, however, that the anti-anti-vax population are not completely exempt from this ridicule. Most of the general population, including the readers, have most likely taken the over-the-counter drug acetaminophen (also known as Tylenol), which has been proposed to be implicated in the onset of this disorder, from a study shown in 2009. Children with autism were shown to have decreased levels of sulfate and glutathione, chemicals crucial in detoxifying acetaminophen, and ironically are decreased when taking acetaminophen as well.
Even more so, a recent study in 2018 revealed possible implications regarding the aggravation of autism by use of the common antibiotic amoxicillin (also known as Augmentin)after Tylenol use, which are prescribed often to patients with infections (even when mild). Amoxicillin/clavulanate decreases glutathione, metallothionein, cysteine, and dehydroepiandrosterone (DHEA), are also found to be decreased in autistic children particularly due to the gut flora in the body, and its effects aggravated by the use of Tylenol. Although not prevalently as exposed, the herbicide glyphosate (also known as Roundup) was found to be exponentially implicated in the onset of autism as well (Good, 2018).
THE GUT BACTERIA AND AUTISM
Obviously these toxins are not the singular cause of autism, but it is indeed studied with empirical evidence. Particularly interesting and often disregarded is the importance of the gut microbiome in the body. These effects of beneficial bacteria are often thought of as physical, but the influence they have on the brain is nothing less than significant. In a recent study done on rodents in 2018, the microbe Lactobacillus reuteri was found to be implicated in the social deficits in mouse models of autism. And although not directly studied, keep in mind that the bacterial genus Lactobacillus was found to be highly susceptible to inhibition by the herbicide glyphosate (Roundup).
How was this study achieved, and how significant were the results? These researchers used mice that had lacked a gene called Shank3B, which effects mimic the social deficits that are commonly shown in autism. These mice were found to have a decreased amount of the L. reuteri bacteria in their gut microbiome compared to the wildtype (normal) mouse with an intact Shank3b gene, as shown in the figure below.
However, it’s not enough to make the association with L. reuteri and these social deficits without evidence. In order to see if they indeed had social deficits and if L. reuteri was responsible for these social deficits, they put the Shank3b knockout mice or the wildtype (WT) in a chamber with another mouse and recorded the amount of time these former mice interacted in their vicinity both with and without the latter mice. As seen in the figure below, Shank3b knockout mice showed decrease interaction time compared to wildtypes. And amazingly, giving these social deficient mice the bacteria L. reuteri showed a significant effect on their interaction times, comparable to the wildtype mouse.
Not only does this show that a simple bacteria in the gut microbiome was responsible for these social deficits, but also that these mice were able to be rescued from these social deficits. If that doesn’t convince you, another autism mouse-model, called BTBR mice, were used and the exact same results regarding L. reuteri and its rescue on their social deficits.
More detail was gone into this bacteria’s role specifically in the brain, but I will keep it short. Oxytocin is a chemical that is responsible for social reward in animals, and if autism mouse models are given this chemical, social deficits are able to be rescued. When L. reuteri is given to these mice, these oxytocin levels are increased, as shown in the figure below.
SO WHAT DOES THIS ALL MEAN?
We have shown that in autism mouse models exhibiting social deficits, lowered levels of the gut bacteria L. reuteri are found. This bacteria affects oxytocin levels in specific parts of the brain that is typically known to be responsible for the social reward(although not as simple as that) behavior in many animals.
All in all, we can rescue these autism-like mice and make them more social by simply giving them a type of bacteria that they lack in their gut.
Once again, this is not the only possible mechanism of autism, but rather just one implication of many. On top of that, it is impossible to say that these experimental mice have exactly the autism spectrum disorder, but rather they are the proposed and recognized model. However, this does not discredit the scientific evidence and the significant effects gut bacteria has on the brain, and how we may be one step closer to finding the cause. And although this article may not convince you that certain things will or won’t cause autism, scientific evidence is necessary to truly understand a disorder or disease, and it works one step at a time.
References:
Good, Peter. (2017). Evidence the U.S. autism epidemic initiated by acetaminophen ( Tylenol ) is aggravated by oral antibiotic amoxicillin/clavulanate ( Augmentin ) and now exponentially by herbicide glyphosate ( Roundup ). Clinical Nutrition ESPEN. 23. 10.1016/j.clnesp.2017.10.005.
Sgritta et al., Mechanisms Underlying Microbial-Mediated Changes in Social Behavior in Mouse Models of Autism Spectrum Disorder, Neuron (2018), https://doi.org/10.1016/j.neuron.2018.11.018
Good P. Did Acetaminophen Provoke the Autism Epidemic? Altern Med Rev. 2009; 14:364–72
