Autism's roots: mix of chance and genetics

March 16, 2007|By Dennis O'Brien | Dennis O'Brien,Sun Reporter

Researchers probing the roots of autism say they've found fresh evidence that the disorder, like cancer, could be a tough one to conquer. That's because it's really a constellation of related diseases - with a wide range of genetic underpinnings.

In a study released today, scientists say that children who are the sole cases of autism in their families are five times more likely to have a particular genetic mutation than autistic youngsters in families in which the disorder has shown up repeatedly.

That confirms what experts have suspected for years: that there might be dozens of genetic anomalies responsible for the symptoms now collectively diagnosed as autism spectrum disorders.

"I think it says something fundamental about autism, that you can kind of think of it as a collection of rare syndromes. Each might have a different genetic basis, but they produce a common set of features. Autism is easily as complicated as cancer," said Jonathan Sebat, lead author of the study and an assistant professor of genetics at the Cold Spring Harbor Lab.

Sebat added that parents of autistic children shouldn't be discouraged by the cancer analogy. Unlike cancer, autism doesn't cause growth of tumors or lead to a cascading of symptoms that eventually kills the victim.

"We don't see that snowball effect with autism," he said.

Sebat's study was published today in the journal Science.

Autism is a complex disorder characterized by an inability to socialize and express thoughts. In some cases, children can become totally withdrawn from society. The disorder is often accompanied by behavioral problems and is usually diagnosed by age 3.

The Centers for Disease Control and Prevention found last month that one out of every 150 8-year- olds demonstrated symptoms of autism.

For parents, the disease can be devastating.

Heather Thoms-Chesley's daughter, Victoria, started having problems when she was 9 months old. She developed an aversion to being touched and preferred to be left alone. Eventually, she started having extreme tantrums and crying fits, and sometimes she bit at her hands till they bled and pulled out her hair in clumps.

"It was a very scary time for us, and for her," said Thoms-Chesley, a 37-year-old Parkville resident and mother of four who is co-president of the Baltimore-Chesapeake Chapter of the Autism Society of America.

Victoria, now 9, was diagnosed with Rett syndrome, a form of autism, when she was 26 months old. She has since progressed to the point where she now is in a Girl Scout troop, can walk to a grocery story and sit while she is fed at a dinner table. She also attends Harford Hills Elementary School and Ridge Ruxton, a Baltimore County school for children with special needs.

None of Thoms-Chesley's other children has autism, and she knows of no one in her extended family with the disease. But she worries now about the possibility of autism developing in her youngest son, who is 2 1/2 . Symptoms can develop up to age 3.

"It's something that's always in the back of my mind," she said.

She said autism research may help, but she and other parents are more encouraged by the support and advice they provide to one another.

"There's no magic bullet, but it's just a matter of steady and constant intervention," she said.

Researchers have known for years that some forms of autism have genetic links.

Researchers using DNA from 1,200 families, living in 19 countries, recently found that a gene known as neurexin 1 and a newly identified region of chromosome 11 may play critical roles in the disorder. Previous studies have found links among 20 different chromosomes.

But Sebat's study focused on comparing autism that could be caused by spontaneous genetic mutations with those rooted in genes passed from parents to children.

"We wanted to test the hypothesis that small anomalies that occur in the genome are a possible cause of autism," he said.

Sebat analyzed the DNA of blood taken from 118 volunteers who were sole members of their families with autism, along with 77 volunteers from families with two or more autistic members and 196 volunteers from a control group without autism.

Sebat was looking for mutations that occur when a person's DNA is duplicated in the production of sperm and eggs before fertilization. It's common to have mutations in the duplication process that delete tiny portions of the original DNA. Such mutations are known as copy number variations.

Sebat found that children who were the sole autistic members of their families were far more likely to have copy number variations than those who had inherited autism and those in the control group without autism.

The study also sheds light on the complications involved in trying to identify the genes causing autism, experts say.

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