Autism Study Rebuts Various Explanations of Increase In Cases
California researchers, in a new study, manage simultaneously to clarify and deepen the mystery about the skyrocketing number of childhood autism.
The study by scientists at the University of California, Davis, rebuts theories that experts have offered over the years to explain the increase in such cases nationally. But it remains for other researchers to explore the reason—or reasons—for the rise in cases of autism, a brain disorder that profoundly affects the ability to communicate and form relationships.
For example, the researchers—whose study was confined to California—found nothing to back one popular explanation: that increased public awareness about the condition has led to better diagnosis. Population increase is not to blame either, they say. And the researchers also say the number of cases was not affected by changes over the years in the definition of autism, or criteria for its diagnosis.
“Autism is on the rise in the state, and we still do not know why,” said Dr. Robert S. Byrd, a pediatric epidemiologist at UC-Davis, who was the principal investigator for the study. “The results of this study are, without a doubt, sobering.”
The study also explored a theory that an influx of autistic children into the state for services caused the leap in cases. But the researchers found that nearly 90 percent of the children in the study had been born in California. Therefore, they concluded, the increase in autism cases was, in effect, indigenous and not solely or even primarily the result of immigration or migration.
In recent years, educators across the United States have seen large increases in the number of students identified as autistic. ("Sharp Rise Seen in Identification of Autistic Pupils," Oct. 20, 1999.) As those numbers continue to rise, researchers like those in California have been grappling for answers.
Though autism has no cure, children who receive appropriate early treatment, including educational intervention, can show great improvement, and in some cases go on to lead relatively normal lives. Providing such treatment has put a financial strain on some school districts, however. Twenty years ago, between two and five cases of autistic disorders were reported per 10,000 people nationwide. Now, the disorders have been identified as affecting as many as one in 500 people, making it more common than childhood cancer or Down syndrome.
Spike Prompts Scrutiny
A 1999 report by the California Department of Developmental Services found a 273 percent increase in autism cases between 1987 and 1998. The alarming increase prompted Gov. Gray Davis and the legislature to commission the $1 million study by the UC-Davis scientists.
Researchers for the project examined data for 684 children from English- and Spanish-speaking families. The researchers looked at two age groups—7- to 9-year-olds and 17- to 19-year-olds—from families of 375 children with a diagnosis of full-syndrome autism and 309 children with a diagnosis of mental retardation.
First of all, the authors found, the diagnostic criteria used by California’s treatment centers has not changed over the years. So they considered whether more children in the older group had been misdiagnosed as mentally retarded, when they should have been determined to be autistic. But the percentage of misdiagnosis was nearly the same in each group. Of the 124 older children and 185 younger children classified as mentally retarded, only 18 percent of each group met the criteria for autism.
“While this study does not identify the cause of autism, it does verify that autism has not been overreported … and that some children diagnosed with mental retardation are, in fact, autistic,” Dr. Byrd said.
About a third of the parents of the autistic children said their children had shown symptoms by the age of 18 months. Such symptoms usually start to manifest themselves before a child turns 3. Some parents reported their children with autism had gastrointestinal symptoms, including constipation and vomiting, in the first 15 months.
Parents of children with autism in the study said they believe the disorder may be caused by genetics or by events in pregnancy or birth.
Since autism diagnoses began to surge, some parents and others have blamed the increase on the measles vaccination that is given to children at around 18 months. Until recently, the vaccine contained a mercury-based preservative, which some believe can cause brain damage in children. But the study found no evidence that the spike in autism cases was caused by the vaccine. Previous studies on autism likewise have shown no such connection.
Robert Beck, the executive director of the Autism Society of America, an advocacy group based in Bethesda, Md., said the study showed the need for further research.
“Now that this has been done at the state level with clarity and professionalism, it needs to be replicated at the national level,” Mr. Beck said. “We need answers, and we need them now.”
Vol. 22, Issue 9, Page 10Published in Print: October 30, 2002, as Autism Study Rebuts Various Explanations of Increase In Cases