[NATURE VS. NURTURE]
By: Kathryn Lowe, MS, CGC, Genetic Counselor, Center for Autism Research, The Children’s Hospital of Philadelphia
ASD is complex in many ways, including finding the cause. In the world of genetics, ASD is considered a
complex disorder, meaning that it is not a result of a single genetic cause, but rather the interaction of
genes and environmental factors. For other complex disorders like heart disease and Type 2 diabetes, it
is known that these disorders run in families, and that lifestyle choices can influence the development of
symptoms. For ASD, the nature of the interaction of genes and
environmental factors is less clear.
Numerous studies have shown that genetics play a large role in ASD, but a
recent study1 urges researchers not to forget about the influence of
environmental factors. The role of genetics in ASD is supported by studies
of identical twins that have shown that when one twin has ASD, about 90%
of the time, the other twin does too. But what about the other 10%?
These cases suggest that something else in involved too.
So what makes one child more likely to develop ASD than another? That is
the question researchers are looking to answer. The answer lies in how
genes interact with each other and with environmental factors (e.g.,
pollution, infection, etc.). Only about 15% of individuals with ASD have an identifiable genetic change
that is the cause of their ASD. As technology improves and more individuals have genetic testing, this
number will increase. However, just as no two individuals with ASD are exactly the same, neither are
two individuals with the same genetic change. Therefore, the influence of environmental factors
impacts how the genetic change affects each individual.
The interaction between genes and these environmental factors are not well understood now.
However, learning more about this interaction will hopefully have a positive effect on how ASD is
diagnosed and treated. Knowing which factors make someone more likely to develop ASD could lead to
closer monitoring, earlier diagnosis, and more effective treatments.
1
Hallmayer, J., Cleveland, S., Torres, A., Phillips , J., Cohen, B., Torigoe, T., Miller, J., Fedele, A., et al. (2011). Genetic
heritability and shared environmental factors among twin pairs with autism. Archives of General Psychiatry, 761767.