While there is no dispute that the prevalence of autism
spectrum disorders (ASD) is on the rise, what is in question are the reasons
for it. Genetics is recognized to play a major causal role in ASD. But over the
past 5-10 years there has been a growing body of research examining the
contribution of environmental factors. What are those environmental factors,
and are there ways for families to mitigate these risks?...
The evidence suggests that there is a connection between
increased maternal and paternal age and the risk for autism. What we don't know
at this point are the mechanisms…
Another etiology being investigated is the social
determinants that affect a person's health. In other words, parents who have
children at an older age may do so for multiple reasons, including both
biological and social reasons. The reasons that they have a child later in life
may also be tied to increased risk for ASD….
There is a lot of interest in antidepressant medication and
the risk for autism, and I agree that there's mixed evidence. It's also
important to consider, similar to the concept of advanced maternal age, that
there are medical, psychiatric, and social factors that may influence a reason
why a mother is on that medication in the first place. Those factors may be
tied to the reasons for the increase in risk for autism….
Implicit in the whole discussion around medications are
these underlying genetic and social determinants that people bring into a
pregnancy…
I think infections are important to consider. We can think
of them in two categories: There are infections that have a direct effect on
brain development, and then there are the infections that cause an inflammatory
or fever response that indirectly affects brain development.
In the first category, we think about infections like
cytomegalovirus (CMV) and, more recently, the Zika virus…
The role of an immune response is one that we know less
about, but it's definitely a subject of investigation currently. We know that
any sort of fever or infection—influenza, upper respiratory infections, any
sort of bacterial or fungal infection—that causes an immune response or a fever
during pregnancy causes an inflammation response and a cascade of biological
events that may have an effect on brain development and potentially an
increased risk for autism…
The research that looks at infectious immune responses and
autoimmune responses does overlap. There is some evidence that having a mother
with an autoimmune disease is associated with an increased risk for ASD.
We know that neurodevelopmental disabilities in general can
be linked to things like alcohol consumption and fetal alcohol spectrum
disorder. We know that maternal smoking puts children at increased risk for
neurodevelopmental disability. Interestingly, autism is not specifically linked
to both of those factors, but neurodevelopmental disabilities, in general, are.
In terms of other lifestyle factors, such as nutrition,
there are no specific diets linked to risk for autism. However, there is some
general dietary advice that should be given. For example, foods rich in folic
acid are important during pregnancy because folic acid is tied to good brain
development. Avoiding certain toxins in food, like mercury, is also important
to decrease the risk for injury to brain development.
There are several studies that have linked environmental
pollutants to autism risk. Two conducted in California and one in Taiwan suggest
that there might be exposures in the environment, including water and air
pollutants, that increase the risk for autism. However, a more recent study
conducted in twins in Sweden did not find an association…
I do think that the gene–environment interplay is a key
concept in autism risk. It may come down to certain genetic risk factors that
put a child at risk for vulnerabilities to environmental exposures…
I think the really important concept to understand when
talking about risk factors for autism is to begin by recognizing that some of
these are controllable and some of them are not. We must differentiate between
them and be sure that an expectant mother knows the difference.
Again, those factors that are controllable are things like
folic acid consumption and avoidance of alcohol and smoking. But
noncontrollable factors include certain genetic risk factors. For women who
have a child with autism and are contemplating a second pregnancy, a
conversation about genetic testing would be important.
http://www.medscape.com/viewarticle/882781_1
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