Study: Childhood Rise in Autism Cases Real
But Reason for the Increase Remains Unexplained
March 7, 2005 - Since the 1990s, there's been a dramatic increase in
among school-age children.
The data are from the U.S. Department of Education, and the report hints that the increases seen with time are real.
Research has suggested that the rise in autism could be largely explained by changes in diagnosis, with children who might have been classified as mentally retarded or speech impaired before the 1990s now being classified as autistic.
Lead researcher Craig J. Newschaffer, PhD, says the Department of Education figures do not show this, but he adds that the increase in autism may never be fully understood.
"I don't know if we are ever going to be in a position to explain what has gone on over the last decade," he says. "The hope is that with the surveillance programs that are now in place we will be in a better position to understand future trends."
Earlier findings from the CDC and others have suggested as much as a tenfold increase in autism and related disorders during the last decade of the 20th century.
The study does not answer the question as to why autism is increasing. But the national data don't show a decrease in other learning disabilities. Trends for mental retardation and speech and language impairment remained unchanged.
This suggests the increase in autism is not the result of an across-the-board increase in special education classification, say the researchers.
Trend May Be Leveling Off
Newschaffer and colleagues from an autism tracking center at the Johns Hopkins Bloomberg School of Public Health analyzed national special education data collected from 1992 to 2001.
The findings are reported in the March issue of the journal Pediatrics.
The research offers intriguing early evidence that the upward trend in autism cases may be beginning to level off. But Newschaffer cautions that the finding may be misleading.
He says a change in 1997 that allowed children up to the age of 9 to be classified as "developmentally delayed" may explain the apparent leveling of autism cases. Before 1997 the diagnosis was used only for children 5 and under.
It is possible, Newschaffer explains, that children with this label who would have been reclassified as autistic after age 5 are now being diagnosed when they are older.
"We will need a few more years of data to determine if the rise in autism is really leveling off," he says.
Early Diagnosis Is Key
The most recent figures indicate that as many as one in 166 children in the U.S. is autistic or has an autism-related disorder, such as Asperger syndrome.
Despite a growing awareness of the importance of early diagnosis, the new report suggests that many children are still being diagnosed at older ages.