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Increase in Autism Baffles Scientists
October 18, 2002
By SANDRA BLAKESLEE
Trying to account for a drastic rise in childhood autism in
recent years, a California study has found that it cannot
be explained away by statistical anomalies or by a growing
public awareness that might have led more parents to report
the disorder.
But the study's authors, who reported their findings
yesterday to the California Legislature, said they were at
a loss to explain the reasons for what they called an
epidemic of autism, the mysterious brain disorder that
affects a person's ability to form relationships and to
behave normally in everyday life.
Autism is on the rise in the state, and we still do not
know why, said the lead author, Dr. Robert S. Byrd, an
epidemiologist and pediatrician at the University of
California at Davis. The results are, without a doubt,
sobering.
As diagnoses of autism have increased throughout the
nation, experts and parents have cast about for possible
explanations, including genetics, birth injuries and
childhood immunizations. The California study found that
none of these factors could explain an increase of the
magnitude reported there - more than triple from 1987 to
1998.
Dr. Catherine Lord, a professor of psychology and
psychiatry at the University of Michigan who is a leading
authority on autism, said it was unclear whether the
California findings applied to other states.
The federal Centers for Disease Control and Prevention is
working in 13 states to look at the apparent increase in
autism cases, said Dr. Frank DeStefano, an epidemiologist
at the agency. So far, there is no reliable count of autism
cases nationwide, since criteria and reporting practices
vary from state to state.
The California study was prompted by a 1999 report from the
state's Department of Developmental Services, which
reported that the number of children with full spectrum,
or profound, autism had increased by 273 percent, to 10,360
in 1998 from 2,778 in 1987. The study did not deal with
milder forms of the disorder, like Asperger syndrome.
The numbers were surprising, Dr. Byrd said. The traditional
estimate was that 4 or 5 children out of 10,000 might
develop autism. Instead, it appeared that 10 children in
every 10,000 were seriously autistic, meaning they suffered
from a brain disorder that left them unable to speak or
compulsively performing repetitive motions like flapping
their arms or rocking.
After the period studied, the number of autistic children
continued to rise, to 18,460 cases as of July 2002,
according to the California Department of Developmental
Services.
In response to the study, the legislature directed the MIND
Institute, an autism research center at the University of
California at Davis, to investigate.
We wondered if the increase was real, Dr. Byrd said.
Maybe we were doing a better job of finding cases. Maybe
there was an increase in awareness of autism. The movie
`Rain Man' was very popular.
California has a system of 21 regional centers that
diagnose developmental disorders and provide services to
children with them. Dr. Byrd and his team mined these
centers for data.
Researchers sent questionnaires to the parents of 684
children with full-spectrum autism or mental retardation.
About half were teenagers, born from 1983 to 1985; the
others were ages 7 to 9, born a decade later.
If the criteria for diagnosing autism had changed in those
10 years or if the definition had broadened, the mystery
would be solved, Dr. Byrd said. But the standards used to
diagnose full-spectrum autism were the same in both age
groups, he said.
Some people suggested that the centers might diagnose
autism so families would receive more generous state
assistance. But the centers have no incentive to do so, Dr.
Byrd said, since they do not receive more state financing
for identifying more children with disabilities.
The study also considered whether children in the older
group were incorrectly classified as mentally retarded,
when they were in fact autistic. But the rate of
misdiagnosis was about the same in both groups, Dr. Byrd
said.
Still another possibility - that large numbers of families
with autistic children had moved into California - was
discarded when it turned out that most children in both
groups were born in California. A general increase in
population accounted for about 10 percent of the rise in
autism, Dr. Byrd said. The rest remains a mystery.
There also were no significant differences over time in
sex, race or parental education. Parents of the older
children were more likely to report mental retardation
along with autism, but the finding did not explain the
rising incidence.
About a third of parents in both groups reported that their
children began to regress around the age of 18 months, Dr.
Byrd said. They suddenly lost the ability to say words and
stopped making eye contact. Many
