Podcasts: The Researcher’s Perspective
Studying Autism and Mercury, with Irva Hertz-Picciotto
An estimated 1-1.5 million Americans live with autism, a neural disorder characterized by impaired social interaction and communication. Some research suggests environmental factors play a role in autism, while other findings point to a genetic basis. More recently there's been a heated public debate about whether autism is caused by the mercury in vaccines commonly given to children. In this podcast, Irva Hertz-Picciotto discusses the implications of research comparing blood mercury levels of autistic children with those of typically developing children. Hertz-Picciotto is an environmental epidemiologist with the Medical Investigation of Neurodevelopmental Disorders (MIND) Institute at the University of California, Davis, and the first author of "Blood mercury concentrations in CHARGE Study children with and without autism."
Transcript (PDF Version 93 KB)
AHEARN: It’s The Researcher’s Perspective. I’m Ashley Ahearn.
Between one and one and a half million Americans live with autism. It’s a neural disorder characterized by impaired social interaction and communication and it’s the fastest growing developmental disability.
But scientists are struggling to figure out what causes autism.
Some research shows that environmental factors are at play, while other findings point to our genes.
More recently there’s been a heated public debate about whether or not autism is caused by the mercury in vaccines commonly given to children.
Dr. Irva Hertz-Picciotto is an environmental epidemiologist with the MIND (Medical Investigation of Neurodevelopmental Disorders) Institute at UC Davis in Sacramento, California.
She compared the levels of mercury in the blood of autistic children with the levels found in typically developing children, and her findings were recently published in Environmental Health Perspectives.
Dr. Hertz-Picciotto, thanks for being here.
HERTZ-PICCIOTTO: Thank you for having me.
AHEARN: Could you start by telling us about your study? What did you find?
HERTZ-PICCIOTTO: Ok, we looked at children who had been diagnosed with autism, and we confirmed those diagnoses, and then we compared them with a group of children who were developing typically. We looked at the mercury in their blood, and we also looked at sources of mercury such as the diet to see how that might relate to the levels of mercury. What we found was that initially the children with autism appeared to have lower levels of mercury than their typically developing counterparts. When we looked further we discovered that that was because they had a different diet. In fact, they took in less mercury because they ate less fish, and fish is one of the major sources of mercury in the human body. Once we accounted for the differences in intake we discovered that in fact the levels were really quite similar between the two groups.
AHEARN: Now why would autistic children be eating less fish?
HERTZ-PICCIOTTO: Anecdotally we know that children with autism tend to be picky eaters. One of the features of autism is called an “insistence on sameness” so these children tend to like to have the same routine every day, and that might include their food choices that might be less variable than other children. So we think that’s probably what’s going on, but quite clearly fewer of them ate fish, and among the ones who ate fish they ate less fish.
AHEARN: I know celebrities like Jenny McCarthy are pointing the finger at vaccines and the mercury in vaccines as a cause of autism. What’s your take on that?
HERTZ-PICCIOTTO: Well, in this study we did look at mercury-containing vaccines that had been given in the last 90 days as a way of trying to see if that also predicted their levels. It turned out that very few of these children had had a vaccine of that type partly because most of the vaccines that contain mercury are no longer in use although the influenza vaccine still does contain thimerosal.
AHEARN: So if autistic kids have the same blood mercury levels as typically developing kids, can we rule out mercury as a potential cause of autism?
HERTZ-PICCIOTTO: Not from this study. That was not the design of this study. We will have to look at that kind of question following children over time. When we take a blood level of mercury we’re really looking at the recent exposures because mercury has a half-life of a few months. So it declines fairly rapidly, and that means that we did not have a picture of what their exposures might have been really early in life, say the first year of life or even in utero because what we were looking at was postdiagnosis levels of mercury. So we’re not looking at mercury as a cause of autism, but we are looking at how these children, what they look like, in terms of their body burden of mercury and specifically looking at the blood.
AHEARN: This mercury research we were just talking about is just one part of what’s called the CHARGE study—which you lead at UC Davis. What does CHARGE stand for? Tell us about this study.
HERTZ-PICCIOTTO: Sure. CHARGE stands for Childhood Autism Risks from Genetics and the Environment. It’s a very large comprehensive study. So far we have about 1,300 families enrolled. About half of them are families with a child who has either autism or an autism spectrum disorder. And the other half are divided between children that we recruit from the general population, whom we then check to make sure the child is developing typically, and another group of children, what we call controls, who have developmental delay but not autism.
AHEARN: So what are you looking at in this population? What are your major focuses of research with this large group?
HERTZ-PICCIOTTO: Well as the title gives it away: genetics and the environment. We define “environment” very broadly to include everything from the chemicals that might be in household products used in the kitchen, in the home, in the yards, on the pets, and also diet, medications, things in the water, things in the air, infectious agents as well, and then we are looking at those also in relation to the inherited genes that the child may have.
The CHARGE study requires us really to go back in time and reconstruct what were the exposures at the time the fetus was developing? What were the exposures around the time of birth and the first year of life? Because we are really seeing these children at ages 2–5, but we really strongly believe that the exposures that led to autism happened much before that.
AHEARN: How do you talk to the families that are participating in your study with the autistic children? What do you say to them when they ask you what caused this to happen to their child?
HERTZ-PICCIOTTO: For most cases of autism there is probably not one single factor—probably not one smoking gun. And I say this to scientists as well. I think there are people in both the scientific and the lay community who believe that there’s going to be one thing—somebody’s going to find THE answer to this question of what is causing autism, and it really is not looking like that’s the case. It’s looking like this is very much a multifactorial condition. The causation, therefore, might be an accumulation of these insults that finally at a certain point overcomes the ability of the organism to recover and to be able to tolerate, so there may be sort of a threshold and beyond that things start to deteriorate in the way in which the brain works.
AHEARN: When you look ahead at the CHARGE study and the work you’re doing with that, where do you see your research heading? What are the kinds of questions you hope to be answering in the future?
HERTZ-PICCIOTTO: We would really like to integrate the gene and environment fields in our work. The geneticists have been working very hard over the last decade trying to identify what genes are involved in contributing to susceptibility to autism. I think many of them think they are finding the causes of autism and have not quite recognized how important environment probably is. Some recent developments coming from the genetics field, however, does seem to suggest that genes and environment are interacting. These developments are in the area of epigenetics, and epigenetics is looking at not the actual genes themselves but molecules that attach to the double helix and affect how tightly it’s wound, for instance, and therefore affect how those genes are expressed.
AHEARN: And those molecules could come from, say, pollution or the environment—is why this is important?
HERTZ-PICCIOTTO: Exactly. Exactly. Those molecules come from the environment, and how they’re integrated into the genome could be determined by other environmental factors.
AHEARN: Dr. Hertz-Picciotto, why do you do this research? Do you think there will be a cure for autism in our lifetime?
HERTZ-PICCIOTTO: Well, I can’t predict the future. I do think we’re going to find causal factors, and I do think we’re going to able to intervene on those factors and maybe prevent cases of autism, and I think the people who are researching looking for cures and treatments are also making progress in that area. But it’s slow, and I think part of the slowness is that we don’t fully understand the underlying biology. So, you know, it’s the discovery. It’s wanting to have a job where you’re helping people, and in the long run, you know, I hope that we’ll be finding some of the causes of autism and contributing to actually preventing cases in the future.
AHEARN: Dr. Hertz-Picciotto, thanks very much.
HERTZ-PICCIOTTO: Thank you.
AHEARN: Dr. Irva Hertz-Picciotto is a chief researcher with the MIND Institute at UC Davis in Sacramento, California.
AHEARNS And that’s The Researcher’s Perspective. I’m Ashley Ahearn. Thanks for downloading!
Ashley Ahearn, host of The Researcher’s Perspective, has been a producer and reporter for National Public Radio and an Annenberg Fellow at the University of Southern California specializing in science journalism.