Air Date: Week of March 12, 2010

The structure of the insecticide chlorpyrifos. Until 2001, the chemical was used in homes and other places where children could be exposed. It is still widely used in agriculture. (Source: Wikimedia Commons)

The majority of autism research has focused on finding a genetic link to the disorder. But genetics only account for a quarter of all cases. Dr. Philip Landrigan of Mount Sinai School of Medicine tells host Jeff Young we should look to possible environmental links to autism, including the effects of chemical exposure on a fetus’ developing brain.

Transcript

YOUNG: The Centers for Disease Control estimate six out of every thousand U.S. children are diagnosed with some form of autism. The apparent increase in autism has alarmed parents and stymied scientists searching for a cause. Dr. Philip Landrigan argues in a medical journal that we should look to our environment for answers on autism. He’s a professor of pediatrics and community and preventative medicine at the Mount Sinai School of Medicine. Dr. Landrigan thinks a sustained focus on chemical exposures in the womb could tell us more than genetic studies have.

LANDRIGAN: I’ll begin by pointing out that there has been some very elegant genetic research done over the past five or ten years that has very successfully identified a number of genes and gene mutations that are responsible for a certain number of cases of autism. All together these genetic causes are responsible for something like 20 or 25 percent of cases. Well, that’s very important work and it’s very important to know that there are genetic causes, but at the same time those findings leave the causation of something like 75 percent of cases of autism unexplained.

YOUNG: So, genetics alone can’t explain this, what evidence do we have that environmental exposures might be a cause here?

LANDRIGAN: We know from other research on toxic chemicals that the developing human brain is very vulnerable to environmental toxins, we know about lead, we know about mercury, we know about PCBs, we know about certain pesticides, and for each of those chemicals we know that if the developing brain is exposed to the chemical early in development, especially in the early months of pregnancy, that the potential is very high for injury to the developing brain.

The second line of evidence I would call proof of principle. And this is the finding that there is a short list of chemicals that have been directly found to be linked to autism. The fact that early life exposure to these drugs can cause autism in certain children says to me that it’s possible other drugs, other environmental chemicals might also be responsible for some cases of autism.

YOUNG: Now, also in this list that you have here you have a pesticide, a pretty commonly used pesticide.

LANDRIGAN: Yes, well, this is the most recent finding that a particular pesticide known as Clorpirifos, and organophosphate pesticide, is associated with pervasive developmental disorder, which a form of autism. There are more than 100 synthetic chemicals measurable in the bodies of virtually all Americans. So, we know that pregnant women, we know that children are being exposed to these chemicals.

The real problem is that we don’t know the potential toxicity of 80 percent of these high volume chemicals. In other words, we just – no testing has ever been done to determine whether these chemicals are safe or not, and as a pediatrician, I find this very worrisome that we’re allowing children to be exposed to chemicals whose possible hazard is simply not known.

YOUNG: We should also talk about the focus on vaccines. There’s some much attention to vaccines as a possible link to autism. How has that affected the overall field of looking for a real possible cause here?

LANDRIGAN: The question of the possible link between vaccines and autism is clearly a question that needed to be addressed. And approximately a dozen high quality studies were launched. It turns out now that not one of them has found any epidemiological connection between vaccines and autism. It’s time to begin to look systematically at other potential environmental causes of autism to see if we can find the triggers and then do something about them.

YOUNG: There’s a lot of attention right now on reforming toxic chemical regulation and on increasing scrutiny on certain chemicals of concern. What evidence are you seeing that people are taking autism into account when they do these things?

LANDRIGAN: Well, I think people are beginning to connect the dots and realizing that there exists at least the potentiality, at least the possibility, that certain untested chemicals that are in children’s environments may be contributing to neuro-behavioral problems in children and the possibility exists that autism is among those.

The chemicals that I would put at the top of my list of suspicion are chemicals that fulfill two criteria: number one, they’re widely distributed in children’s environments, or the environments of pregnant women; and number two, there are chemicals where we already have some suspicion from experimental studies or from studies in adult workers exposed occupationally that these chemicals are neurotoxic.

YOUNG: You know, in a way this is pretty scary because the upshot of what you’re suggesting here is that there are exposures that in many cases may be well beyond our control that may determine whether or not our child is autistic, but on the other hand, it also implies we can figure this out and do something about it.

LANDRIGAN: Yes, at the end of the day, I think the message here is fundamentally optimistic. I strongly believe that for 500 years knowledge has guided medicine, evidence has guided prevention, and time and again we have shown as a society that when we understand the causes of disease we can take action to prevent it.

YOUNG: Dr. Philip Landrigan at the Mount Sinai School of Medicine in New York. Thank you for your time.

LANDRIGAN: You’re very welcome, Jeff. Thank you.

YOUNG: Dr. Landrigan’s proposal appears in Current Opinion in Pediatrics. For more information, go to our website, l-o-e dot org.

 

Links

Click here to read the abstract of Landrigan's paper on the environmental factors of autism.

To listen to a longer version of LOE's interview with Dr. Landrigan, click here