Swedish study suggests cases of autism aren’t on rise
In the largest study of its kind, a Swedish group has determined that actual autism rates probably have not changed in recent years, even though diagnoses of autism cases continue to climb.
The research, led by Sebastian Lundstrom and colleagues at the University of Gothenburg, found that about 1 percent of those in an ongoing study of twins met the criteria for having autism, even though the number of officially diagnosed autism cases in the country’s national health registry had climbed steadily over a 10year-period. The power of the study, published last month in the British Medical Journal, comes from the fact that Sweden has comprehensive health records for its population, and the research covered nearly 20,000 twins whose families were asked about their symptoms, along with diagnostic records for more than a million children born between 1993 and 2002.
Because the study counted autism diagnoses of children up to age 10, it covered a period up until about 2012.
In a recent telephone interview, Mr. Lundstrom said there is no reason to believe the Swedish experience with autism is much different from that in the U.S. or other nations, and he said there is no evidence to suggest that twins have a different rate of autism than the general population.
The national registry in Sweden includes all the official diagnoses for autism spectrum disorder, which more than doubled from 0.23 percent in 1993 to 0.5 percent in 2002. That rate is lower than the 1 percent prevalence found among the twins, but that may be because the national registry uses a conservative definition of the disorder. In another Swedish study last year that looked at all diagnoses for autism among teens living in Stockholm County, the autism diagnosis rate was about 2.5 percent.
“My personal view is that the autism rate might lie between 1 percent and 2 percent, depending on which lens you look at autism through,” Mr. Lundstrom said, “and our study suggests the [actual autism rate] has been fairly steady for decades.”
The official U.S. autism rate put out by the federal Centers for Disease Control and Prevention is now 1 in 68 children, or about 1.5 percent, based on an extrapolation from school records and official doctors’ diagnoses in 11 communities.
has come in children with higher IQs, including The official U.S. rate has those with Asperger’s syndrome. more than doubled in recent Current figures show years, from 0.67 percent in that half of all children in the 2002 to the current rate, leading U.S. diagnosed with autism some to believe that environmental have IQs above 85, the official toxins or other factors threshold for those who are have created an explosion not mentally retarded. of new cases. The official CDC Dr. Minshew said many of statement says cautiously, these children simply were “We don’t know what is causing not recognized as having autism this increase. Some of it decades ago, and “people may be due to the way children will often say to me now, I are identified, diagnosed know there were a couple and served in their local communities, kids in my class who must but exactly how have had this. Or people will much is unknown.” say, ‘This is what my brother
Studies like the one in Swedenarguethatalmostalltheincrease must have had; we never understood why he failed his has been due to greater graduate program.’” awarenessofautismandanexpansion Autism is marked by in the number of childrenwhogetthediagnosis. three main characteristics: difficulty with social relationships,
Nancy Minshew, director problems with of the University of Pittsburgh’s communication and repetitive Center for Excellence behaviors or narrowly in Autism Research, says that focused interests. she thinks the actual autism Much of the debate over the rate may be higher than the autism numbers has revolved one calculated in the Swedish around whether something in study— upto3percent— but the environment — air and she agrees with the study’s water pollution, pesticides or main conclusion. certain drugs, for instance
“My view is that the autism — might have triggered a rise numbers have gone up, in autism. but the number of people who Brian Lee, an epidemiologist are affected is actually unchanged, at Drexel University in which is what they Philadelphia, participated in are saying in this paper.” the Swedish teenager study
She said much of the that found a prevalence rate growth in the official numbers of 2.5 percent.
“A lot of papers show that most of the [autism] increase is due to diagnostic substitution and better awareness and those sorts of factors, but I’m still not entirely convinced it’s not a real increase.” The increases could partly be caused by environmental damage that causes new mutations in a child’s genome, he said. “We happen to live in one of the more polluted times in recent history.”
But Mr. Lundstrom, the Swedish researcher, isn’t buying that argument. “I am convinced there are several environmental factors that could affect autism,” he said, “but I don’t think they’re increasing. One issue that people have raised is pesticides, like living next to a big cornfield, but no one can convince me that pesticides were less toxic in the 1970s.”
In epidemiology, having a large population to study leads to more powerful results, Dr. Minshew noted.
“I think the Swedish research design was strong, and I think their results were solid. When you have 20,000 twins and 1.1 million total people, you can get very strong results.”