Autism Spectrum Disorder: Nature v. Nurture

Autism-spectrum disorders are caused only by genetic factors, not environmental factors …right?  “Wrong,” says a new study conducted by researchers from Stanford University, UC Berkeley, Autism Speaks and several other institutions.

Twins studies of autism have, to date, mostly focused on identical twins who share exactly the same genetic material.  In this population, when one twin had autism, so did the other at a rate of about 60%.  This was not surprising to researchers who believe an almost independent connection between autism and genetics.

But this new study included fraternal twins in the study group.   In fraternal twins, whose DNA is not identical, the rate of coinciding autism was a shocking 50%, suggesting that environmental factors are significantly at play in causing autism.  For the researchers, whose interest had principally been in genetic causes, this is likely to trigger a significant shift in focus.

Other experts commenting on these findings suggest that the non-genetic factors contributing to autism may be similar to those associated with disorders such as schizophrenia and bipolar disorder.  These environmental causes may include advanced parental age, frequent pregnancies in a short period of time, poor prenatal care, low birth weight and other factors.

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 a 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. Understanding both the genetic and environmental causes of autism may help researchers discover ways not only to treat the disorder, but to prevent it in the first place.

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