Autism: What to Make of the Dramatic Rise in Cases

For years the autism community's most powerful public-relations weapon has been a striking statistic: an estimated 1 in 150 children have the diagnosis. Now it appears that estimate is actually too small. According to two new studies, the number of kids diagnosed with autism or a related disorder in the U.S. is closer to 1 in 100.

The new data has everyone who cares about autism abuzz. But, as with so many issues connected to the disorder, no one can quite agree on what it means.

One of the new studies, published in Pediatrics, is based on a survey of more than 78,000 parents. Researchers asked them if doctors had ever diagnosed any of their children with autism or a related disorder on the autism spectrum, such as Asperger syndrome. More than 1,400 of the parents said yes. If those numbers represent the population at large, that means 673,000 American kids likely have a form of autism.

Parent surveys often yield unreliable data because respondents may misremember or misunderstand what doctors have told them. But the Pediatrics study is backed up by a second, more reliable set of data collected by the Centers for Disease Control and Prevention (CDC). The full results aren't out yet, but on Friday, CDC researchers reported that one in 100 8-year-olds has been labeled with a disorder on the autism spectrum. That number is based on the same methods that yielded the original 1-in-150 statistic—so using CDC data alone, it's certain that autism diagnoses are on the rise.

That, however, is where the certainty stops. In the contentious autism community, two debates are constantly simmering: How many more children actually have autism now than had it in the past? And what are the underlying causes? The new numbers don't just fail to resolve either of these debates—they turn up the heat on both.

A rise in autism spectrum diagnoses doesn't necessarily mean a precisely corresponding rise in actual cases. Doctors may be inflating the numbers inadvertently by diagnosing the disorder more readily than they used to. Many doctors now diagnose autism and related disorders in children they might once have classified differently. Also, they may be more likely to give a child a diagnosis if they think that will help the child's parents obtain special-education services from public schools. Some are even willing to diagnose autism as a co-morbid condition in "people with clearly identifiable genetic disorders, such as Down syndrome—which is something that nobody would have dreamed of doing in the past," says Roy Grinker, a George Washington University anthropologist (and father of a child with autism) who believes the new numbers largely reflect an increase in diagnosis rather than actual illness.

At the same time, there's good evidence that more children actually are suffering from autism. In January, researchers at the University of California, Davis analyzed a seven- to eightfold increase in diagnoses in their state since 1990. Twenty-nine percent of that increase could be explained by doctors' diagnosing cases they might not have diagnosed before, says Irva Hertz-Picciotto, who led the study. Another four percent came from doctors diagnosing cases in younger children. But that still leaves 67 percent of the huge increase unexplained—and, says Hertz-Picciotto, that part is real.

Here's where the second debate comes in: if more kids are developing autism-spectrum disorders, what's causing the increase? As with most illnesses,both genetics and environmental factors almost certainly play a role: As the popular analogy goes, genetics loads the gun and the environment pulls the trigger. Kids may be genetically predisposed to autism, but they won't develop it unless they're exposed to outside factors that affect the activity of their faulty genes.

Scientists know something about the genetics of autism. They've found genes that are loosely linked to the disorder on practically every chromosome. But they know less about environmental factors, which could include heavy metals, pesticides, flame retardants, or many other culprits. A vocal minority of advocates, of course, is also concerned about vaccinations, although there's no solid evidence that vaccines are linked to autism. "More than ever, environmental factors are being recognized as important," says Cathy Rice, a CDC researcher who led the agency's new study. "But our research tools just are not as good for understanding them."

Many autism research advocates feel that environmental factors have gotten short shrift from the National Institutes of Health, which has largely focused on genetics so far. The new data may help them make their case as the government winds up a review of its research priorities. The new numbers don't explicitly point toward any single environmental factor, but genetics alone can't account for such a steep rise in the number of cases, because genes don't change that quickly.

Still, that's no reason to stop doing genetic research and focus exclusively on the environment. The two types of research can complement each other. If scientists can figure out which genes are turned on or off (or up or down) in autism, they'll be able to narrow their long list of potential environmental villains and focus on those that affect the relevant genes.

Amidst the controversy over how much of the increase in autism diagnoses is real and what's causing it, there's a third puzzle in the new data that's been generally overlooked: the phenomenon of "lost diagnoses." Why did 38 percent of parents in the Pediatrics study whose children were at one time diagnosed with autism report that their kids no longer had the condition? Geri Dawson, chief scientific officer for the advocacy group Autism Speaks, says it's possible that these kids no longer have classic symptoms of autism but continue to have other problems—anxiety disorders, tics, or forms of attention-deficit hyperactivity disorder. "We really don't know how children who lose their diagnosis fare after time," she notes. It's possible that some were misdiagnosed in the first place. It's also possible that there's good news hiding in the Pediatrics study—that many of the kids who started with an autism diagnosis managed to get better, probably after extensive behavioral therapy.

Ultimately, there's only one thing that everyone in the autism community agrees on—the need for more funding. That's something people outside the community seem to agree with, too. In February, the federal government funneled $85 million in stimulus grants toward new autism research at the National Institute of Mental Health. The Health Resources and Services Administration, part of the U.S. Department of Health and Human Services, also has $48 million in new funding for autism research this year. It'll be a long time before any of that money translates into findings that can help kids with autism and send the 1-in-100 number back down. But perhaps new research will tell us how the number got so high in the first place.