Wednesday, August 2, 2017

The environment and ASD risk: Putting it together

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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