An
international team of researchers led by Canadian scientists has honed
in on the genetic underpinnings of autism, one of the most common and
debilitating developmental disorders in children.
Previous studies have suggested between eight and 20 different
genes are linked to autism, which affects an estimated one in 165
children.
“But the new data suggests there are more genes involved than
we would have expected before,” said Stephen Scherer, a senior
scientist at the Hospital for Sick Children and co-author of the study
published online yesterday in the journal Nature Genetics. He estimates 100 genes could be involved or work in combination to cause autism.
Scherer said it took a global effort to co-ordinate the
research, a feat that could not have been accomplished by one lab
alone.
The five-year collaboration, part of the Autism Genome
Project, involved more than 130 scientists in 50 institutions in 19
countries, and cost million.
“To make this happen is unbelievable,” said Scherer, who led
the Canadian team with Peter Szatmari, director of the Offord Centre
for Child Studies in Hamilton.
Autism spectrum disorder can cause a range of symptoms in
children, including repetitive behaviours and impaired language
development and social interaction. The disorder affects x four times
as many boys as girls.
To search for autism-susceptibility genes, the scientists
collected DNA samples from 1,600 families from around the world with at
least two members with autism spectrum disorder. They then scanned
their entire genome to look for regions shared by people with autism.
The search led scientists to a previously unidentified area on
chromosome 11, which they now believe harbours genes that increase the
risk for autism.
They also used a technology pioneered at the Hospital for Sick
Children, where they looked for copy number variations — long stretches
of genetic material that either have missing or extra DNA. They found
shared copy number variations in between 5 and 10 per cent of the
families.
The analysis also uncovered a link between autism and the
deletion in part of a gene known as neurexin 1, one of a family of
genes important in communication between neurons in the brain.
The findings point the way for scientists to dig deeper into
the genome to look for similar regions and molecular pathways that
could cause autism.
James Kennedy, head of neuroscience research at the Centre for
Addiction and Mental Health in Toronto, called it “a landmark study”
that will have long-ranging implications for autism research.
“We expect many genes cause autism, maybe dozens,” said
Kennedy, who was not part of the study. “To even find one of them is a
great step forward.”
Szatmari said researchers have long known that autism is an inherited genetic disorder, but no one knew how it was passed on.
“We now know which haystack the needle is located in and, even
more than that, we also have a better idea of where that needle is
located,” he said. “We really will be able to now, in the next five
years, to hone in on candidate genes and candidate regions to identify
those genes and DNA sequences that seem to have gone wrong or have led
to autism.”
The findings will help researchers come up with diagnostic methods for autism spectrum disorders, said Szatmari.
“We’re still diagnosing them too late,” he said. “If we can
derive diagnostic tests for some forms of autism ..... and lower the
age of diagnosis to 24 months or 18 months, that will be really
important. The earlier children get interventions, the better the
outcome will be.”
Every week parents of autistic children ask Wendy Roberts, a
developmental pediatrician and co-director of the autism research unit
at Sick Kids, whether there are prenatal tests to screen for autism.
“At this point, we say that we can’t.”
The study won’t have any immediate impact on clinical practice,
said Roberts, a co-author of the study. It will take time to design a
prenatal test for autism, precisely because there are so many genes
involved.
Roberts collected data from Toronto-area parents, including
John. He didn’t want to use his last name because of the huge stigma
still attached to autism spectrum disorders.
In the past, many parents blamed themselves for the onset of
the disorder, looking to diet or even childhood immunizations for the
cause.
John and his wife always believed there was nothing they could
have done to prevent their 6-year-old son Michael’s autism and the
research confirms it. Now they know Michael — who has difficulty
communicating with people — has a deletion in one of his chromosomes.
Their older son does not have autism.
“How do you ensure that genes are passed on intact without any
missing things? You can’t,” John said. “That’s just nature. We’re not
going to fret about it and we encourage all parents not to fret about
it, either.”
They knew the study wouldn’t lead to a cure for Michael or even a new treatment for his symptoms.
“But it’s a start,” said John. “It may help him when he’s an
adult. And in 10, 20 or 30 years it may lead to treatments for other
children that have this type of diagnosis.”
Again, good to see the Autism Genome Project getting attention. This is the first article that I've read that had a quote from real parents. The father says they now know that their son has a deletion in one of his chromosomes. Nature is the cause, he says.
I myself believe that my son's problems are genetic, but I still wonder if it's something else is the cause, something that is inadvertently my fault? It would be nice to lay these thoughts to rest like that father has done.