CHICAGO — Mention autism to parents, doctors and scientists these days, and among an earful of different theories will emerge a common nod of agreement: The perplexing condition is not nearly as rare as once was thought.
As recently as a decade ago it was estimated that only about 4 per 10,000 children were affected. Research now suggests the rate may be at least 10 times higher.
The numbers have fueled debates over whether there's been a true surge of cases and whether environment or genetics could be the cause. Some parents and research advocates blame vaccines despite recent evidence to the contrary.
But many mainstream scientists point to two much less worrisome explanations: The definition for autism has changed and schools now offer more educational services to autistic children.
In 1991, the U.S. Department of Education made autism a new, separate category for special education services offered at public schools. Those services tend to be broader and more intensive than for other disorders, including mental retardation. There's evidence that the 1991 change prompted what some call "diagnostic substitution," said Dr. Fred Volkmar, a Yale University autism researcher.
"Autism is kind of a fashionable diagnosis," Volkmar said. "Everybody's interested in getting better services."
Statistics seem to back up the theory. Department of Education figures show that the number of children getting services for mental retardation fell from 553,262 in 1991-92 to 532,362 in 1992-93. During those same years the number of children getting services for autism swelled from 5,415 to 15,580.
The change in school services and the definition, along with research showing that early intervention could help, raised awareness of the condition.
Autism used to be thought of as "the kid who sits in a corner watching the record player go around and around. Everybody said that's what autistic is and anything else is not," said Chicago pediatrician Dr. Joel Schwab.
Schwab said that like many doctors, he may have inadvertently diagnosed autistic youngsters a decade ago as being mentally retarded, or with nondescript behavior problems.
Now, autism is increasingly recognized as "being more than just the classic picture," said Schwab.
Molecular biologist Andy Shih, director of research and programs for the National Alliance for Autism Research, says that whether or not there's been a surge in cases, "what is clear is that autism is a serious public health issue.
"With potentially 1 million Americans afflicted with this disorder," Shih said, "it is no longer something that is rare or seldom seen."
The impact has reached far outside the medical realm.
Many schools are struggling to provide enough services to affected children, funding for research into causes has grown, and lawsuits blaming vaccines are proliferating.
"There's just so many kids who have been affected, it's hard to find somebody who doesn't know somebody who has a kid with autism," said Liz Birt of Wilmette, Ill., whose 9-year-old son, Matthew, is autistic.
Within seven blocks of their suburban Chicago home, five other children also are afflicted.
Autism even ended up in a debate over a last-minute provision attached to Homeland Security legislation enacted last fall. The provision, aimed at protecting drug makers from lawsuits over vaccine-related injuries, prompted vocal protests in Washington in January by parents who think childhood vaccines cause autism.
Much has been learned about autism in the past half century. But many key questions remain. Researchers don't know if a single gene or many are involved, or possibly different ones in different cases.
Some think environmental factors might trigger the disease in genetically susceptible people. Potentially plausible but unproven triggers range from illness during pregnancy to soil toxins, electromagnetic waves and even vaccines, though strong evidence so far suggests the shots are safe.
"There's just too much we don't know," said Dr. Edwin Cook of the University of Chicago.