If you’re not scientifically minded, you might be unaware of the potential link between epigenetics and autism. From the moment children are conceived to the moment they begin to interact with the environment, they’re indirectly exposed to factors which could affect their development. In short, epigenetics is the study of how your behaviors and environment can impact the way your genes work.
Let’s break it down further! A fetus’ interaction with the environment takes place through the mother. For this reason, throughout pregnancy, physicians recommend certain foods, diets, or regimes for the mother to support the fetus’ brain development. Of course, there are many uncontrollable factors that could be present in the environment during development that could affect a child’s growth.
Some of these environmental influences can impact development at the genetic level. Changes or mutations caused by environmental or extraneous circumstances are known as epigenetic modification. There are many neurological conditions some researchers believe to be a result of epigenetic mutations and one of these is autism spectrum disorder (ASD).
As the name suggests, autism is a spectrum of several symptoms such as loss of acquired skills, communication issues, limited or restricted interests, and varying forms of challenges in everyday life. For this reason, it is believed that a combination of various genetic and environmental factors can account for the phenotypic expression of autism.
Although biology researchers and geneticists haven’t narrowed down the exact cause of autism, epigenetics may be able to explain some of the causes of autism based on genetic studies and how genes react to certain environmental influences. Let’s find out if there’s a link between epigenetics and autism.
What is epigenetics?
The theory of epigenetics was first proposed by Conrad Waddington in the early 1940s. By his definition, epigenetics is “the branch of biology that studies the causal interactions between genes and their products that give rise to the phenotype”. In simple terms, and as explained above, epigenetics is the study of how the environment and how relationships to it can affect change in how our genes work.
Epigenetic modifications don’t change the DNA sequence but change how our body reads the sequence. In a sense, epigenetics changes the expression and regulation of gene products which in turn determines the phenotypic expression (physical expression). When genes become altered, this is referred to as mutations. Factors that can cause epigenetic change include diet, lifestyle, and exposure to toxic substances (Metere & Graves, 2020).
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Here are examples of some diet and lifestyle choices that have been identified to modify the expression of genes:
- Foods which contain substances such polyphenols or selenium (antioxidants present in fruits and vegetables) can cause DNA methylation (Metere & Graves, 2020)
- Large quantities butyric acid (a substance found in cheeses) or sulforaphane (a substance found in broccoli) can modify histones (basic proteins which associate with DNA) by inhibiting histone deacetylase (Metere & Graves, 2020)
- Curcumin (sometimes found in cosmetics, food flavoring, or coloring) is known to have antioxidant effects. When used at high doses, it may produce toxic and carcinogenic effects (cause cancer) in healthy cells. This is possibly due to the post-translational modification of histones (Metere & Graves, 2020)
- Diet rich in fat can also cause hypermethylation of specific DNA segments to reverse the effect of tumor suppressor genes (Metere & Graves, 2020)
There are three types of epigenetic change, namely DNA methylation, histone modification, and noncoding RNA. Some of these have been mentioned already, so let’s look at each briefly and define what they are:
- DNA methylation aka gene silencing
This occurs when a chemical group known as a methyl group is added to the DNA. This addition occurs at specific places and usually blocks the proteins used to read the DNA. DNA methylation can be reversed through a process called demethylation. “Typically, methylation turns genes “off” and demethylation turns genes ‘on’” (CDC, 2020).
- Histone modification
When DNA coils into chromosomes, they wrap around proteins called histones. If the DNA wraps too tightly, it stops important proteins from running along the DNA to “read” it. According to the CDC: “Some genes are wrapped around histones and are turned ‘off’ while some genes are not wrapped around histones and are turned ‘on’.”
- Noncoding RNA
Our DNA is used to make RNA, and the process can make both coding and noncoding RNA. Noncoding RNA is used to regulate gene expression and coding RNA is used for signaling in response to certain stimuli. Coding RNA therefore serves as an indicator for transcriptional activity.
Every type of epigenetic modification takes place before a child is born i.e. during fetal development. As the child grows and develops, epigenetics help to identify how a cell functions. Epigenetic changes occur throughout a person’s lifetime. For example, the amount of DNA methylation at childbirth is usually higher than the amount found in the elderly population (CDC, 2020). The interesting thing about epigenetics is that unlike genetic changes, some epigenetic mechanisms can be reversible.
How is epigenetics linked to autism?
DNA methylation is the most common form of epigenetic regulation which can cause transcriptional silencing (when the transcription of a specific gene is silenced). DNA methylation is found to be linked to several pathophysiology of neurological disorders such as autism spectrum disorder (ASD) (Eshraghi, et al. 2018).
Some studies have found inconclusive evidence about the link between epigenetic modification and autism. An example of such research is how ROR-α transcripts in blood lymphocytes haven’t yielded positive results to differentiate between neurotypical and autistic children. On the other hand, some studies have found methylation biomarkers for autism. Of these, the PRRT1 gene for example is lower in methylation in the temporal cortex and cerebellum in autistic brains (Eshraghi, et al. 2018). In addition, analysis of the methylation patterns in the human placenta (human placental methylome analysis) shows higher methylation in autism disorders (Eshraghi, et al. 2018).
Diet is a hot topic that is believed to contribute to the epigenetic development of ASD. According to a meta-analysis study by Pu et al., 2013, countries whose folate acid fortified diet is high showed a higher association of MTHFR C677T polymorphism (an enzyme) compared to those without food fortification. The enzyme MTHFR C677T polymorphism is associated with an increased risk for developing autism—the reason being that the enzyme plays a key role in DNA methylation during neural development (Eshraghi, et al. 2018).
Can autism be caused by genes?
Some genetic tests may be used to identify specific genes in a cell that have been found to increase susceptibility to autism but, unfortunately, there’s no specific genetic test that can accurately determine whether a person is positively autistic or not. This is mainly because several factors or gene expressions cause autism symptoms, which likely explains why autism symptoms vary from one individual to the next.
The more we study our genes, the more developed genetic testing becomes. As knowledge around genes increases, this assists our understanding of the relationship between genotype and phenotype as well as the role of epigenetics in ASD.
Although some research positively correlates epigenetic differences or mutations to autism, some studies on this topic don’t support this conclusion or they show inclusive results to support this finding. Autism research is still growing and there’s still so much for us to learn from it.
For example, one study reported no difference in global methylation between control groups and the autistic brain, while another claims that gene expression in autism may be due to mechanisms which regulate genes as opposed to the belief that gene methylation accounts for the expression of ASD symptoms (Eshraghi, et al. 2018). These debates and contradictory findings of research go to show there’s still so much to learn about the role of epigenetics in autism.
Topics such as these are important, especially for families affected by autism, to understand the biological reasons for their child’s or family members’ experience of autism. Understanding epigenetics might also help educate parents on choosing the best medical treatment methods to assist their autistic child’s development.
CDC, 2020. What is Epigenetics? https://www.cdc.gov/genomics/disease/epigenetics.htm#:~:text=Epigenetics%20is%20the%20study%20of,body%20reads%20a%20DNA%20sequence
Eshraghi, A. A., Liu, G., Kay, S. S., Eshraghi, R. S., Mittal, J., Moshiree, B., & Mittal, R. (2018). Epigenetics and Autism Spectrum Disorder: Is There a Correlation?. Frontiers in cellular neuroscience, 12, 78. https://doi.org/10.3389/fncel.2018.00078
Metere, A., & Graves, C. E. (2020). Factors Influencing Epigenetic Mechanisms: Is There A Role for Bariatric Surgery?. High-throughput, 9(1), 6. https://doi.org/10.3390/ht9010006
Pu, D., Shen, Y., and Wu, J. (2013). Association between MTHFR gene polymorphisms and the risk of autism spectrum disorders: a meta-analysis. Autism Res. 6, 384–392. doi: 10.1002/aur.1300