Is Autism Genetic or Environmental?
In recent years, autism spectrum disorder researchers have been commonly divided on the question: is autism genetic, or environmental? A recent study conducted in 2019 has perhaps finally answered this question. The study, the largest of its kind, involved over 2 million people across five countries and discovered evidence that autism spectrum disorders are 80% reliant on inherited genes.
While it’s great to make progress on this elusive topic, there are still more questions that this revelation begs. Like, how is autism inherited? And, what role do the remaining 20% of environmental factors play in the development of autism spectrum disorder?
Let’s take a closer look at the causes of ASD, both genetic and environmental, and how individuals develop this condition.
Genetic Causes of Autism Spectrum Disorder
Dr. Andrew Adesman, a director of developmental and behavioral pediatrics at Cohen Children's Medical Center in New Hyde Park, N.Y, explains in the conducted study that "we are not yet able to identify a specific genetic cause for autism in many children." He believes the next step is "to identify more of the different specific genetic differences or abnormalities that lead to autism in an individual child or family."
Some research has indicated that in about 2 to 4 percent of people with autism, rare gene mutations or chromosomal abnormalities are thought to be the cause of the condition. This is often seen as a feature of syndromes that also involve additional signs and symptoms affecting various parts of the body. Changes, or mutations, in the DNA is thought to lead to autism, in the form of a genetic variant. These common variants have subtle effects and may work together to contribute to autism.
So, is there an ‘autism gene’? Not likely, but there are several conditions associated with autism that stem from mutations in a single gene, such as fragile X and Rett syndromes. As of right now, there is no indication of an autism gene, meaning there is no gene that’s consistently mutated in every person with autism.
How is Autism Inherited?
These mutations are most often inherited from parents, and can be common or rare, as well as arise spontaneously in an egg or sperm. Spontaneous mutations that arise after conception are usually ‘mosaic,’ which means they affect only some of the cells in the body. When cells affected by these mutations are fewer, the contributions to autism traits become milder.
Genetic causes of autism spectrum disorder may also explain why males are more likely to have ASD than females. Girls with autism tend to have more mutations associated than boys, while boys sometimes develop mutations from unaffected mothers. Some research suggests that girls may be somehow resistant to mutations that contribute to autism.
The risk from gene variants combined with environmental risk factors like parental age, and birth complications are yet to be identified, but some factors may potentially help determine an individual's risk of developing autism spectrum disorder.
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References
MedlinePlus. (2021, December 8). Autism Spectrum Disorder. Retrieved January 28, 2021
from https://medlineplus.gov/genetics/condition/autism-spectrum-disorder/
Mundell, E.J. (2019, July 17). Autism Largely Caused by Genetics, Not Environment: Study.
Retrieved January 28, 2021 from
Zeliadt, Nicholette. (2021, May 28). Autism genetics, explained. Retrieved January 28, 2021
from https://www.spectrumnews.org/news/autism-genetics-explained/