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MICHELE NORRIS, host:

This is ALL THINGS CONSIDERED from NPR News. I'm Michele Norris.

ROBERT SIEGEL, host:

And I'm Robert Siegel. A new study links autism to subtle changes in a wide range of genes. The finding suggests that autism can have many causes. It also suggests that whatever triggers autism usually occurs long before birth.

NPR's Jon Hamilton reports.

JON HAMILTON: Autism can run in families, but most children with autism come from families without any history of it. That's been a puzzle for researchers studying the genetic roots of the disorder.

So a team of researchers took a close look at the genes of more than 260 families. Some had members with autism; others didn't. Jonathan Sebat led the study. He's a geneticist at the Cold Spring Harbor Laboratory in New York. Sebat says the goal was to compare the genes of autistic children with the genes of their parents.

Mr. JONATHAN SEBAT (Geneticist, Cold Spring Harbor Laboratory): By comparing the two, we could find mutations that were in the child that was not inherited from either parent.

HAMILTON: It turned out that children with autism were much more likely than other kids to have these so-called spontaneous mutations, genetic changes that were not present in either parent. These mutations affected bits of genetic code that tend to appear more than once. They're like duplicate copies of certain pages of a book.

In many children with autism, some of these extra copies were deleted. For example, Sebat says one child in the study was missing a copy of the gene for oxytocin, a hormone that seems to influence social behavior.

Mr. SEBAT: That child has one copy of oxytocin instead of the normal two copies, and that may have resulted in the corresponding decrease in the levels of oxytocin.

HAMILTON: Which could have affected normal social development. But Sebat says that in other children with autism the deletions affected other genes.

Mr. SEBAT: There may, in fact, be many genes, I would speculate 100 or more, that play some role in cognitive development and when they are altered could cause autism.

HAMILTON: That's many more than researchers have found involved in inherited autism. And Sebat's work is causing a lot of excitement among autism researchers. Ezra Susser is an epidemiologist at the Mailman School of Public Health at Columbia University.

Professor EZRA SUSSER (Epidemiology, Columbia University): I think what it does is it changes our thinking about what kind of genetic causes are important, and knowing that, it changes our thinking about what kind of environmental causes are important. Because I think everybody believes that there's an interplay of genes and environment in most diseases, and that would be true for autism too.

HAMILTON: Susser says the sort of mutations found in the study tend to occur in eggs or sperm before conception, or in the earliest stages of an embryo's development. That suggests things like exposure to vaccines after birth probably aren't the main causes of autism. Susser says the study suggests a new direction for researchers seeking the causes of autism.

Prof. SUSSER: It doesn't mean that we should stop looking for in-utero exposures. It doesn't mean that we should stop looking for early-life exposures, but it does mean that we should start looking for exposures that might be pre-conceptional also.

HAMILTON: Susser has already shown that older fathers are more likely to have mutations in their sperm and more likely to have a child who is autistic. He says researchers need to ask whether a parent's exposure to certain chemicals has a similar effect.

In the meantime, the new research offers at least one practical application: Parents who already have a child with autism could undergo genetic testing to see what sort of mutations are present. If the mutations are spontaneous rather than inherited, future children would have no special risk for autism. The research appears in the journal Science.

Jon Hamilton, NPR News.

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