Un article intéressant du National Post. En anglais malheureusement...
The findings published in the journal Nature help confirm the strong role that genes play in autism, and also suggest that small genetic disruptions may begin in the parents’ eggs and sperm.
The findings published in the journal Nature help confirm the strong role that genes play in autism, and also suggest that small genetic disruptions may begin in the parents’ eggs and sperm.
Lisa Bond spent years trying to understand why her son, Joshua, wouldn’t make eye contact, threw fits when she tried to change his socks, and had so much trouble learning to speak.
It turns out Joshua, now 14, is missing a small chunk of DNA on chromosome 16 — a deletion so profound it impaired his neurodevelopment, causing autism and serious language and learning disabilities.
For Lisa, the genetic revelation is a huge relief. “Knowing just makes it so much easier to cope,” she says.
For Dr. Stephen Scherer, at Toronto’s Hospital for Sick Children, it is part of a “paradigm shift” in understanding the causes of the baffling disorder that affects almost one in 100 children.
Dr. Scherer and his colleagues have just released the world’s largest genetic study of autism. They scanned the DNA of Joshua and 995 other children with the disorder from Canada, the United States and Europe.
The results, published in the journal Nature this week, show that individuals with autism have almost 20 per more gene deletions and duplicates than normal. Dozens of new “autism risk genes” were also uncovered.
Some children, like Joshua, are missing chunks of DNA. Others carry duplicate stretches of DNA. Some of these so-called “copy number variants” were inherited; others are new and not seen in other family members.
“This suggests that tiny genetic errors may occur during formation of the parents’ eggs and sperm, and these variations are copied during creation of their child’s DNA,” says co-author Dr. Daniel Geschwind, at the University of California, Los Angeles.
Autism spectrum disorders vary widely in severity. They tend to show up as language and social problems in toddlers, and can develop into highly repetitive behaviours, restricted interests and social and communication deficits. Many individuals have serious lifelong disabilities, and some are brilliant. “I have colleagues at the university who have Asperger’s (a mild form of autism),” says Scherer.
It’s long been known genes are involved in autism spectrum disorders, but researchers have spent years — in Scherer’s case, 15 years — trying to home in on the ones responsible.
The study shows there is not a single gene tied to autism but many genes and gene regions, that differ from person to person. The researchers, who plan to test 5,000 more Canadian youngsters in the next few years, expect to find plenty more.
“Most individuals with autism are probably genetically quite unique, each having their own genetic form of autism,” says Dr. Scherer, who led the study that compared the genes of individuals with autism to genes of 1,287 unaffected people.
It revealed that many of genes involved in autism spectrum disorders play a role in production of proteins that affect the way neurons in the brain “grow, differentiate and communicate with each other.”
There was also significant overlap with “intellectual disability genes” previously associated with other mental-heath disorders.
Since many of the genes are tied to the same biological pathway, Scherer says, they provide targets for drug therapies and new treatments.
Having a better read on the genetic players could also mean earlier diagnosis, the researchers say, and could end the long waits parents often endure as they struggle to find out what is wrong with their youngsters.
Ms. Bond says she knew there was something amiss when Joshua was two years old. “It was like he was in his own little world,“ she says recalling how he avoided eye contact, would often “lose it” emotionally and didn’t speak until he was in kindergarten. Specialists confirmed Joshua was autistic when he six years old.
The more detailed genetic explanation only came as a result of the study, which the Bonds joined a couple of years ago. Joshua is now in Grade 8 in Campbellford, Ont., just east of Toronto. He takes special-needs classes but is so good at remembering and reciting facts that he is in regular science classes. “He has an incredible memory,” says Ms. Bond. She says learning about the gene deletion on chromosome 16 is a big help as they deal with Joshua’s ongoing problems. But she says she wishes they’d known years ago as early intervention can help autistic youngsters overcome some of their language and social problems.
“I banged my head against the wall for years,“ says Ms. Bond, who hopes the ongoing research will help families get a much quicker diagnosis.
Dr. Scherer’s team was recently awarded $8.9 million to expand gene testing to include 5,000 more Ontario children with autism spectrum disorders over the next three years. He says the work so far provides genetic clues that may assist in the early diagnosis of autism or related complications in about 10 per cent of the families.
It also means better genetic counselling for affected families. While there are not prenatal tests for autism, the new information about the genes involved does raise the possibility. Dr. Scherer said that knowing a family has a gene variant strongly linked with autism can help with the “decision-making process” for couples thinking about having more children.
There has long been concern and controversy over the rising incidence of autism, which is now said to affect one in every 110 children in North America, and four times as many boys as girls. Environmental factors may play a role, but the researchers say it is still unclear how. They also say there is no evidence of a link to vaccinations given in infancy.
Read more: http://www.nationalpost.com/Research+suggests+genetic+basis+austism+autism+risk+genes+uncovered/3132931/story.html#ixzz0qTqAMphY
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Ce travail majeur vient conforter le récent consensus scientifique, selon lequel l'autisme est provoqué en partie par des "variations rares" ou des modifications de certains gènes. Parallèlement, cela confirme que ces gènes jouent un rôle dans le fonctionnement des synapses cérébrales, rôle qui avait été identifié par l'équipe de Thomas Bourgeron (Institut Pasteur, université Denis Diderot) et celle de Marion Leboyer (Inserm, AP/HP, FondaMental) en 2008.