|By David Kohn
In recent years, autism research has been a battleground. A vocal group of parents, advocates and a few scientists focused on vaccines containing traces of mercury as the lead suspects in the disorder. But most autism researchers were suspicious, arguing that the theory didn’t fit the evidence.Now, with a new Danish study offering the strongest evidence yet
against the vaccine theory, the controversy may give way to a more
baffling question: If vaccines aren’t the culprit, then what is? The range of
theories underscores how little is known about autism, a developmental
illness that afflicts as many as one in 200 American children and makes it
difficult for them to connect with the outside world.
Researchers are looking at a variety of possible mechanisms: Do
“There are a variety of tantalizing trails of evidence,” says Diana
Last week’s issue of Pediatrics published a report on autism cases
“This reaffirms that there is no evidence that thimerosal causes
But some critics called Madsen’s study deeply flawed. Because
Yet even scientists who suspect thimerosal minimize its role in the
Most researchers suspect that autism is a family of disorders with
“Autism is no one thing. It probably has multiple causes,” said Dr. Andy Zimmerman of the Kennedy Krieger Institute’s Center for Autism and Related Disorders.
A combination of abnormal genes – probably between four and 20 –
But genes alone don’t cause the illness. Most experts think genes
Zimmerman, a pediatric neurologist, suspects that immune system
In his most recent work, Zimmerman has found that in some autistics, the brain’s immune cells – the microglia – are overactive. His next step: to find out whether these cells are fighting off an attack or doing harm themselves.
At Harvard Medical School, pediatric neurologist Margaret Bauman
Many scientists think the illness may stem from an oversized brain.
This “neuroproliferation” could explain why autistics often seem overwhelmed by
“There are too many cells, and they could potentially create too much noise,” said Rebecca Landa, director of the Center for Autism. “It’s like sticking your finger in a socket. Their brains can’t channel on the input.”
She is working on a study to measure the levels of neurochemicals
Other scientists are focusing not on the size of the autistic
Men, he says, tend to see the world in terms of systems, while women view it through the prism of emotion and relationship. Autistics – 80 percent of whom are male – show many hyper-masculine traits, he argues.
They focus on details while neglecting the whole, have trouble interpreting
Baron-Cohen is testing testosterone levels in the amniotic fluid of 3,000 children, some of them autistic. His hypothesis: high prenatal testosterone can produce an acutely “male” brain. The hormone may speed development of the right hemisphere, which probably controls these male characteristics.
If testosterone does play a role, prenatal treatments might help the disease. But Baron-Cohen is leery, arguing that “hormonal engineering” could radically alter personality.
“Would we want to intervene?” he asked. “You may make your child more sociable, but also maybe less focused on systems. There could be a cost for that.”
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