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Public Radio's Environmental News Magazine (follow us on Google News)

Environmental Triggers for Autism

Air Date: Week of

The prevalence of autism has increase dramatically in the last decade. (Wikipedia Creative Commons)

New research shows a strong relationship between the environment and autism. Dr. Martha Herbert is a neurology professor at Harvard Medical School. She tells host Bruce Gellerman that this study – which looked at twins - gives new evidence that autism may not solely be linked to genetics, a finding that could dramatically change autism research. Photo: The prevalence of autism has increase dramatically in the last decade. (Wikipedia Creative Commons)


GELLERMAN: There are significant and exciting new findings that fundamentally alter our understanding of what causes autism. For generations, scientists thought autism was essentially a genetic disease - but there's growing evidence environmental factors may play an even larger role. The case is made in a new study of twins in the most recent issue of the Archives of General Psychiatry. To help us understand the study's complex findings we turn to Dr. Martha Herbert - she's a professor of neurology at Harvard Medical School and an expert in the field of autism research. Dr. Herbert, welcome to Living on Earth.

HERBERT: Thank you.

GELLERMAN: So let's look at the methodology that the researchers used - they used, they studied twins.



HERBERT: Because twins are in the same family and they share at least some genes. But identical twins share all the genes and fraternal twins don’t share all the genes - they have maybe 50-50.

GELLERMAN: So if something shows up in the identical twins you’d say, ‘Ah, genetic.’ But, if something shows up in the fraternal twins, you’d say, ‘Mmm, there’s something else going on here.’

HERBERT: Yes, that’s what people have usually said.

GELLERMAN: So these researchers studied, what, about 192 pairs of twins?


GELLERMAN: What did they find?

HERBERT: They found that actually there was more concordance than expected in the fraternal twins, and less in the identical twins.

Repetitive behaviors like stacking can be a behavior associated with autism. (Wikipedia Creative Commons)

GELLERMAN: Concordance?

HERBERT: That means that if one is autistic, then the other is autistic. So usually it has been that 60-90 percent of the identical twins were both autistic, and 0-10 percent were both autistic if they were fraternal twins. And that led people to think that this was, by in large, very, very strongly, a genetic disorder. But to have there be so much match -concordance - in the fraternal twins, and not so much in the identical, suggests that there’s shared environment. What they calculated was that the risk for autism was 38 percent from genetics and 58 percent from environment that twins shared.

GELLERMAN: So it’s a very low number in terms of genetics and very high in terms of environmental issues.

HERBERT: Yes, which is really different from what everybody’s been saying up until now.

GELLERMAN: So what kind of environmental factors could we be talking about?

HERBERT: Well, there are lots of environmental factors that people have been talking about and trying to do research about. It ranges from chemicals to nutrition to exposures like to being living near a freeway – many, many different types of factors.

GELLERMAN: Are there any suspects that perhaps stand out from the crowd?

HERBERT: There are a number of chemicals that it’s a good idea to watch out for. Bisphenol - plasticizers that make plastics moldable. Flame retardants - flame retardants in baby pajamas and in bedding that were not tested for the baby urinating in the bed, which then makes the chemicals float around in the air that the baby then breathes in. Pesticides - be really careful about spraying your house. Find more natural ways of avoiding pest exposure. Pesticides in food - try to eat organic if possible. Don’t microwave in plastic. Look under your sink and clean out a lot of the products, which have long lists of chemicals that you can’t pronounce. There’s lots of ways of cleaning your house with simple products, with vinegar and water and baking soda, and things that are not going to cause problems, that may show up now or later.

GELLERMAN: There’s another new study that suggests that women who take anti-depressants while they’re pregnant have a higher incidence of children with autism.

Martha Herbert (Photo: Anne-Marie Singh)

HERBERT: Right, it’s about double the risk. And it reminds me of another recent study that came out where mothers who did not take prenatal vitamins were 60 percent more at risk of having children with autism. But what’s interesting about that is if the mother, who was not taking a prenatal vitamin, also had a mutation in one of two genes, that make you more vulnerable to the environment, they had up to four and a half times increased risk of having a child with autism.

Dr. Martha Herbert and Bruce Gellerman in the LOE studio. (Photo: Anne-Marie Singh)

GELLERMAN: Now the number of cases of autism is exploding. I think that the Centers for Disease Control says something like 600 percent increase over the last two decades. It’s a national health crisis!

HERBERT: Right, well the numbers are going up. The numbers that are reported in each successive study seem to be higher. The most recent study from Korea was one in 38. That’s a lot, that’s like three percent, which is a lot for something that 15 years ago was 3 in 10,000.

GELLERMAN: In terms of autism spectrum disorder - the dramatic increase - can part of that be understood in redefining it or looking for it more carefully?

HERBERT: There have been a number of studies in the last couple of years trying to figure out whether the autism increases are real, an artifact, or a combination of both. And what it’s looking like is somewhere between half to 2/3 is real, and the rest is some kind of artifact - whether we loosened up the diagnostic criteria, we’re diagnosing people younger, or we’re noticing people we never noticed before.

GELLERMAN: How does this research help us, and what happens next in autism research?

HERBERT: I think this paper is fantastic for saying: ‘Lets pull out the stops and look at everything we possibly can - environmentally.’ We have been putting our eggs so much in the basket of genetics. I have a dear friend who is a geneticist who said, ‘Why don’t you environmental people wait for awhile, we’ll work out the genes and you can sort of do the trimmings.’ Now, looking back, this is not the trimmings. This is not the icing on the cake, it’s the cake.

GELLERMAN: Well, Dr. Herbert, thank you so very much for coming in and helping us understand this very complex and very important topic.

HERBERT: Great, thank you!

GELLERMAN: Dr. Martha Herbert is a Professor of Neurology at Harvard Medical School. Her new book, which comes out next year, is called "The Autism Revolution."



Read the study: Genetic Heritability and Shared Environmental Factors Among Twin Pairs with Autism

Anti-depressants and autism

Martha Herbert’s Website


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