Autism Cases on the Rise
Study Shows Increase Is Real, Not Just Due to Changes in Diagnosis Criteria
WebMD News Archive
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.