A large international team of scientists has discovered rare genetic changes that predispose some people to autism. The complex neurological disorder affects about one percent of children. It impairs their ability to communicate and develop social relationships and, in many cases, causes behavioral difficulties.
The study identifies a number of genetic mutations, called copy-number variants, in the genomes of children diagnosed with autism.
Copy-number variants are segments of DNA that have been duplicated or deleted in the genes of children with autism. Investigators say some of the genetic abnormalities appear to be inherited while others are unique to the autistic children.
In the study, researchers from eleven countries compared the genomes of nearly 1,000 autistic children to 1,300 children without the condition, searching for the rare variants, some of which had been previously implicated in connection with autism. They found these mutations occur 20 percent more often in children with the neurological disorder.
Andy Shih, with the organization Autism Speaks, likens the latest discoveries to pieces of a jigsaw puzzle: "With these findings you are starting to find some of the edge pieces. So, that would provide you with some sort of a framework for looking at how these genes work in autism and leading to the clinical features and how it might work in collaboration with the environment that can lead to some of the autism that we see around us," he said.
Investigators say the copy-number variants in the autistic children disrupt normal functioning in a number of areas, including pathways associated with synapses, the structure between brain cells that allows chemicals to pass electrical and chemical signals to other neurons.
They also found genetic mutations involved in the reproduction and signaling of cells.
Stanley Nelson is a professor of human genetics at the University of California in Los Angeles and co-author of the study.
He says while the mutations make individuals more susceptible to autism, the genetic abnormalities do not automatically mean someone will have the disorder. "It's probably not a hundred percent and we just haven't observed it enough yet. So one of the challenges now is to observe these types of mutations across larger sample sets such that you could determine what is the real risk if you inherit this sort of variant or what's the risk if you have a mutation that your parents didn't have," he said.
Autism is what is known as a spectrum disorder, meaning that people could be only mildly affected, a condition known as Asperger's syndrome, while others with autism are profoundly disabled.
Nelson says his team did not find an association between the number of genetic insertions and deletions and the severity of autism.
To pinpoint the causes of the disorder, Nelson says scientists need to conduct a much larger study decoding the genes that have been implicated in this research. "Each child who's affected has some genetic information in their genome that we would like to learn from. And that's the quickest route to try and dissolve [solve] the riddle that is autism," he said.
An article describing genetic changes in children diagnosed with autism is published this week in the journal Nature.