Environmental Toxins and Autism
By Marcia Zimmerman, C.N.
“It’s time to abandon the idea that a single smoking gun will emerge to explain why so many children are developing autism” Irva Hertz-Picciotto, Ph.D., MPH, University of California, Davis
Last month we explored the role environmental toxins play in autism spectrum disorders (ASD). Epidemiological studies – many just beginning – support the link between autism and the environment. While this important work is ongoing, many scientists are focusing on the specific metabolic pathways that are dysregulated by environmental toxins and the role genes play in autism.
Genetics and Epigenetics
Studies of twins have shown that genes strongly influence the risk of autism. , Moreover autism has been defined as a “complex inherited disease” involving multiple genetic types. Almost nothing is known about interactions among these genes. Certain “clusters” of genes are thought to be involved, and these may be sex-linked. , This helps explain why four times more boys than girls have the disorder. And while genetics is still an important consideration in occurrence of autism, epigenetics is thought to play a much greater role. What is the difference?
Genes are specific regions on DNA (deoxyribonucleic acid) that encode for proteins that orchestrate metabolism. These codes consist of clusters of DNA base pairs that are ‘hard wired” into its structure. To date there are 25 that have been identified as possible candidates for fostering an autism spectrum disorder. Some of these genes have also been linked with other disorders such as developmental language disorders, ADHD, and Down’s syndrome. , From studies of identical and fraternal twins, researchers have found that if one child in a family has ASD, it is highly probable that his or her sibling will also be on the autism spectrum. , Some of the ASD candidate genes have also been linked to specific areas of the brain that appear to be involved in the disorder. The genetic complexity of ASD remains elusive. The new field of epigenetics offers a better explanation for the diversity seen among ASD individuals.
“Epigenetic” refers to the regulation of DNA sequences that does not involve alteration of their actual base composition. This involves “switching” the sequences on or off by attaching small chemicals called methyl groups to certain sites along their DNA. Efficient switching regulates the metabolic processes and it is highly influenced by environmental exposure. Consequently, epigenetic therapies may be an effective pathway for altering the course of ASD because they have the ability to coordinate very large integrated gene networks. Epigenetic therapies might include modifying the child’s diet, reducing his or her environmental exposure, detoxifying the body, and balancing nutrition deficits through supplementation. Let’s take a look at how a known neurotoxin might impact ASD and how this might be addressed through the lens of epigenetics.
Metabolic Dysfunction
A 2010 study by a group of scientists at University of California, Davis, compared blood levels of mercury in autistic children with those not affected to see what effect environment might have on ASD. No differences in blood levels of mercury between the two groups were found. Is it possible that mercury, which we will use as a “model” contaminant, is not involved in ASD? There are two problems with this line of thinking.
- Blood levels of mercury will not show if the child is bio-accumulating mercury in their brain, which is the target organ for mercury storage. The half-life of blood mercury is short; 60 – 90 days and blood is a better gauge of recent exposure. The authors of the above study point out that only 5% of body burdens of mercury are estimated to be in circulation.
- Autistic children are thought to be particularly vulnerable to the effects of mercury because they lack the ability to eliminate it from their bodies through normal detoxification systems.
- Mercury causes epigenetic changes, which may result in the factors commonly seen in ASD. These include oxidative stress, neuro-inflammation, mitochondrial dysfunction, and abnormalities in glutathione, a critical antioxidant and detoxifier. Poor methylation – think genetic switches – is also found in many autistic children.
Epigenetic therapy might begin with biomarker testing to determine bio-accumulation of toxic metals, metabolic abnormalities, nutrient deficiencies, intestinal dysbiosis, oxidative stress, faulty detoxification (glutathione, methylation) pathways, immune dysregulation, and food sensitivities. This is an amazing new approach to ASD and one we will explore in upcoming Zimmerman Files.
Be sure and follow up with more detailed presentations on ASD in my monthly webinar series. Register for the free webinar on Monday September 20th at 8 PM CDT, at https://www.now-university.com/Webinars/. You can also download all of my previous recorded webinars with PowerPoint presentations by going to https://www.now-university.com/Webinars/Archives/index.htm.
References:
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(8)
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(18)
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(22) Ibid.
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(25) James, J.S. op. cit.
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