An exhaustive study of autism in one community has found that the disorder is far more common than suggested by earlier research.
The study of 55,000 children in Goyang, South Korea, found that 2.64 percent — one in every 38 children — had an autism spectrum disorder.
"That is two-and-a-half times what the estimated prevalence is in the United States," says Roy Richard Grinker, a professor of anthropology at George Washington University and one of the study's authors.
The South Korean study probably produced such a high figure because it screened a lot of kids who seemed to be doing OK and included in-person evaluations of any child suspected of having autism, Grinker says.
"Two-thirds of the children with autism that we ended up identifying were in mainstream schools, unrecognized, untreated," he says.
The team of Korean and American scientists who carried out the study, published online in the American Journal of Psychiatry, say the result doesn't mean there's something different about South Korean children.
"There's no reason to think that South Korea has more children with autism than anyplace else in the world," says Bennett Leventhal, another author of the study. Leventhal is also deputy director of New York's Nathan Klein Institute for Psychiatric Research and a professor of child and adolescent psychiatry at New York University Medical Center.
The study's primary message, Leventhal says, is that "if you really go look carefully among all children everywhere, you find that things are far more common than you previously expected."
Previous efforts to identify children with autism have tended to focus on kids in special education classes, or those whose school records show they have language or learning problems.
But that approach has the potential to miss a lot of kids, Grinker says. "What we wanted to do was to go beyond that and pick a medium-sized city where we could look at every child," he says.
The city they chose, Goyang, is not far from Seoul. And South Korea is an ideal place for this kind of study because the government makes sure that every child goes to school.
Until now, South Korean officials and educators have assumed that autism was quite rare. The group's five-year study of children ages 7 to 12 showed otherwise.
"I had some expectation that it's going to be a little higher than the previous studies because we're including children from the general population that have been understudied in the past," says Young-Shin Kim, the study's first author and an assistant professor at the Child Study Center at Yale University. "But the extent — that was a surprise to us."
Many of the children were probably missed because they didn't misbehave and they weren't failing academically, Kim says.
"These children could function at a level that was expected, even though they were having a lot of difficulties with their peers and social engagement," she says.
Also, Kim says, autism carries a severe stigma in South Korea, so some parents may have ignored some telltale behaviors. And she says they were often upset to learn they had a child on the spectrum.
"Some of the parents were yelling at us like, 'You guys are crazy, my child is OK,' " she says. "Some parents are shocked. Some are devastated. But some are like, 'Oh, my God, now it makes sense. Actually, I'm so glad you told me that because I couldn't make any sense out of my child.' "
The authors say maybe people shouldn't be surprised to find that autism is so common. After all, other brain disorders, such as severe depression, affect more than 2 percent of adults; severe anxiety disorder affects about 4 percent.
And the implications of this study are global, Leventhal says. He says there are powerful reasons to identify all kids with autism, even if they aren't failing in school.
"They're socially awkward and they have trouble making friends. They get in trouble because their behavior is a little odd," he says. "And then when we teach them their skills, they actually can fit in better and succeed better."