18 October 2002
in Autism Baffles Scientists
By SANDRA BLAKESLEE
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.
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.
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."
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
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
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.
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
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.
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.
response to the study, the legislature directed the MIND Institute,
an autism research center at the University of California at Davis,
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."
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.
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.
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.
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.
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.
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
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.
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
parents blame vaccinations thatare given around 18 months; until
recently some vaccines contained a mercury-based preservative that
some people believe can cause brain damage in young children. The
study found no evidence that the vaccine was the culprit, Dr. Byrd
more parents of younger children reported constipation and vomiting,
which they attributed to complications from the measles vaccine.
Wheat allergies were also more frequent. But none of these differences
fully explain the increase in autism cases in California, Dr. Byrd
in the study were asked what might have caused their child's autism.
Nearly half the parents in both groups said they did not know. A
third blamed genetics; smaller numbers cited immunizations, birth
injury or environmental factors.
can't explain an increase of this magnitude on genetics," Dr.
Byrd said. "Something else is happening."
know autism has a strong genetic component," said Portia Iversen,
a founder of Cure Autism Now, a research and advocacy group in Los
Angeles formed by parents of autistic children. "But we don't
know what in the environment is interacting with genes to contribute
to this huge increase in cases."