[Paleopsych] MSNBC: As autism cases soar, a search for clues
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Mon Apr 25 19:10:58 UTC 2005
As autism cases soar, a search for clues
http://www.msnbc.msn.com/id/6947652/ et seq.
By Jacqueline Stenson
Updated: 2:58 p.m. ET Feb. 24, 2005
Once a rare diagnosis, it seems there's now an epidemic of autism
sweeping the nation. Many of us know a child with the disorder, and
concerned parents are searching for suspicious signs even in young
babies. But while more kids are being labeled with autism, whether the
condition is truly more common among today's children than past
generations of youngsters is largely unclear.
There's no question that autism diagnoses are increasing, but it's
unknown how much of that is due to greater awareness of the disorder
by doctors and the public, a broader definition of it, a true increase
in incidence or other factors.
"There is a chance we're seeing a true rise, but right now I don't
think anybody can answer that question for sure," says Dr. Chris
Johnson, a professor of pediatrics at the University of Texas Health
Sciences Center at San Antonio and co-chair of the American Academy of
Pediatrics Autism Expert Panel.
Parents who believe the disorder is increasing due to some modern
threat that is damaging the brains of children have pointed the finger
at childhood vaccinations and the mercury-containing preservative
thimerosal that was once widely used in many of them. There are also
suspicions about lead or other toxins in the environment, diet,
viruses and medications. Indeed, some experts say it's possible that
exposures in utero or in early childhood may play a role.
Frustrated parents struggling to cope with a disorder that seemed to
appear virtually overnight understandably want answers. But clear
insights are hard to come by.
Studies done in the 1960s indicated that autism was quite rare,
affecting only about one person in every 2,000 to 2,500, according to
the Centers for Disease Control and Prevention. Other research in 1970
put the figure at one case per 10,000, Johnson says.
Precisely how many people have autism today is unknown. But estimates
suggest there are five to six cases of autism spectrum disorders
(ASDs) per 1,000 people, says Johnson. That roughly equates to as many
as one case out of every 166 people.
It's important to note that today's figures apply to the whole
category of ASDs, which includes autism as well as related conditions
like Asperger Syndrome and Pervasive Developmental Disorder Not
Otherwise Specified. Children with these disorders have varying
degrees of impaired communication and social interaction.
Diagnostic criteria changed dramatically in 1987, broadening the
number of people who could be considered to have ASDs. In decades
earlier, only those with severe autistic characteristics would be
diagnosed with autism; others might have been categorized as mentally
retarded, for example. So making comparisons across decades is
"The frequency of the diagnosis has clearly increased but that doesn't
tell you beans," emphasizes Dr. William Barbaresi, a pediatrician at
the Mayo Clinic in Rochester, Minn.
To get a better picture of autism and its potential causes, Barbaresi
and colleagues examined new cases of autism in Olmsted County, Minn.,
from 1976 to 1997.
Using data on every child living in the county during those years, the
researchers used modern diagnostic criteria to conclude that the
incidence of autism specifically rose dramatically, from 5.5 cases per
100,000 children from 1980 to 1983, to 44.9 cases from 1995 to 1997.
A sharp increase started between 1988 and 1991, a period during which
broader diagnostic criteria for autism were newly in use and increased
awareness of the disorder occurred, Barbaresi says.
Other studies also have failed to link vaccinations to autism,
prompting the Institute of Medicine, an independent group that advises
the federal government, to conclude there is no connection.
But no one knows exactly what causes ASDs, and until they do, much
about these disorders will remain a source of great speculation.
To say that there's a lot doctors don't know about these conditions is
"an understatement," says Dr. Leonard Rappaport, director of the
Developmental Medicine Center at Children's Hospital Boston.
"Most things we don't know," he says.
Rappaport suspects there may be a true rise in ASDs, though he says
it's not at all clear why or to what extent.
To better understand the causes, and hopefully improve diagnosis and
treatment, Rappaport is involved in a new study that is focusing on
genetic underpinnings of the disorders that he says may play a role in
upwards of 90 percent of cases. The federal government also has
organized an international coalition to explore the genetics.
Many scientists believe that ASDs are largely caused by genes. Studies
have shown, for instance, that if one identical twin has autism the
second twin is very likely to also have the disorder. But the risk
isn't 100 percent, suggesting that other factors can contribute, even
if they aren't the main cause.
"I think it's clear that there's a strong genetic predisposition,"
says Dr. Steve Sommer, chairman of the department of molecular
genetics at City of Hope National Medical Center in Duarte, Calif.
One theory behind a cluster of cases of high-functioning autism and
Asperger Syndrome in Silicon Valley holds that people who carry the
genes gravitate toward high-tech professions like computer science
that don't necessarily require a lot of social interaction. And when
these people, who may not have the full-blown disorders, meet and have
children together, the kids could be fully affected because of the
double genetic whammy from both parents.
Down the line, scientists suspect they may find many genes involved in
Sommer's research has shown that a mutation in the neuroligin 4 gene,
which is involved in creating healthy connections between neurons in
the brain, is defective in about 3 percent of people with autism. But
that doesn't mean that everyone who inherits the defective gene will
develop autism, he says. And there are likely many more genes that
play a role in the condition in certain people.
"From a genetic point of view, autism is likely to be many -- perhaps
a hundred or more -- diseases," he says.
But if autism spectrum disorders are truly on the rise, genes aren't
the reason. "The gene pool doesn't change," explains Rappaport. "It
would have to be something that's environmental."
That something -- if it does exist -- remains a huge mystery and a
source of endless worry for parents, especially given that there is
currently no known way to prevent autism.
Rappaport says many parents fear they may have done something to
trigger the problem, like taking their kids to get regularly scheduled
immunizations or exposing themselves to environmental toxins.
"Parents are searching for answers, and they're blaming themselves for
a million different things," he says.
"I can't even imagine all the sleepless nights."
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