Autism Cases on the Rise

Study Shows Increase Is Real, Not Just Due to Changes in Diagnosis Criteria

Reviewed by Louise Chang, MD on January 08, 2009
From the WebMD Archives

Jan. 8, 2009 -- Environmental factors may be partly behind California's eightfold rise in new cases, a new study implies.

Many researchers have believed that the continuous increase in autism cases over the last decade -- particularly the huge increase seen in California -- isn't real, but can be explained by "artifacts."

Among these artifacts are the recent broadening of the diagnostic criteria for autism and greatly increased diagnosis of autism at younger ages. Both these factors could make it seem like there are more autism cases than there were before.

These artifacts do explain part of the rise in autism cases, shows a rigorous study by Irva Hertz-Picciotto, PhD, MPH, chief of the division of environmental and occupational health at the University of California, Davis.

But even taken together, they don't explain even half of the huge increase in cases.

"When you put it all together, this doesn't come close to explaining the increases in the last 10 years," Hertz-Picciotto tells WebMD. "The more you whittle away at this increase, the more you have to say that what is left over is real. ... Given that autism cases keep going up, and can't be fully explained by artifacts, environmental factors deserve serious consideration."


Hertz-Picciotto notes that her study does not account for one potentially huge artifact: The fact that today's parents are vastly more aware of autism than they were a decade ago.

Autism can't be diagnosed unless you're looking for it -- so parent awareness has a huge potential effect on the rise of autism, says Gary W. Goldstein, president and CEO of the Kennedy Krieger Institute and professor of environmental health sciences at Johns Hopkins University.

"There is an enormous increase in awareness. Everybody knows about autism now, and they didn't 16 years ago," Goldstein tells WebMD.

"The awareness thing is very hard to quantify," Hertz-Picciotto says. "But at some point, as more and more parents became aware of autism, the increase should have leveled off. Instead we see a continued increase in autism."

Hertz-Picciotto notes that the lion's share of autism funding is going to genetic studies. She argues that it's high time more effort was put into looking for environmental factors that cause autism in genetically susceptible individuals.


"Time is passing and science has a lot to do to find the real causes of autism," she says. "A lot has changed in the environment over the last 10 to 15 years. And I paint with a broad brush when I say environment: These changes include things like medications people take and assisted reproduction technology as well as what is in soaps and pet shampoos and toothpaste and so forth."

Autism expert Michael L. Cuccaro, PhD, associate professor of human genetics at the University of Miami, praises Hertz-Picciotto's systematic study of the rise in autism cases. He agrees with her that it's time to consider environmental factors as part of the cause of autism.

"I don't think it is premature to look for environmental risks," Cuccaro tells WebMD. "There are environmental risk factors that give rise to a wide range of developmental conditions, and there's no reason to think autism isn't one of them. And papers like this are critical to get to this point. Because you have to convince people it is not explained by all these other factors."


Environmental studies are already under way -- and research organizations are eager to fund them, Goldstein says. But the difficulty goes far beyond funding.

"We only have 20,000 to 25,000 genes. But we have a hundred thousand environmental exposures. How do you control for that?" he says. "And your genes stay the same, while environmental exposures may have come and gone. It is difficult to do these studies -- the problem is not that it isn't thought to be important."

The Hertz-Picciotto study appears in the January issue of Epidemiology. The study is co-authored by Lora Delwiche.

WebMD Health News



Hertz-Picciotto, I. and Delwiche, L. Epidemiology, January 2009; vol 20: pp 84-90.

WebMD Health News: " Thimerosal Down but Autism Rising."

Irva Hertz-Picciotto, PhD, MPH, chief, division of environmental and occupational health, and professor of public health sciences, University of California, Davis.

Michael L. Cuccaro, PhD, associate professor of human genetics, University of Miami.

Gary W. Goldstein, MD, president and CEO, Kennedy Krieger Institute; professor of neurology and pediatrics and professor of environmental health sciences, Johns Hopkins University, Baltimore.

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