New research has identified genetic risk in 50 per cent of autism cases, bringing scientists closer to unravelling the mysteries of the neurological disorder.
Previously, doctors only had the ability to identify about 20 per cent of the genetic risks of autism, a condition that strikes one in 88 people and is considered a growing public-health challenge.
The promising finding came after 32 unrelated Canadian autistic children and their families had their whole genomes sequenced, an expensive process that maps a person’s DNA, or deoxyribonucleic acid, the building blocks of life.
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The research is led by the Hospital for Sick Children’s Dr. Stephen Scherer and the Centre for Applied Genomics lab. It stems from an international collaborative effort to unravel the genomes of 10,000 autistic people by Sick Kids, China’s Beijing Genomics Institute, Duke University and Autism Speaks, a science and advocacy organization.
The 32 Canadians are among the 10,000. The study was published Thursday in the American Journal of Human Genetics online.
“This is really delivering the big jump,” Scherer said. “We go from 20 per cent to roughly 50 per cent where we find, and this important, a genetic variant associated with either autism or an accompanying medical symptom seen in the patient.”
Many autistic individuals also have associated health concerns such as seizures, sleep and anxiety problems, and Fragile X syndrome — a condition causing learning and developmental disabilities. A “genetic overlap” between autism and epilepsy is also often observed, the study noted.
In the 32 families, researchers unearthed a number of genetic changes such as spontaneous mutations, X chromosome-linked alterations and other inherited mutations in four previously unrecognized genes, nine genes previously linked to autism and eight candidate risk genes, the study said.
Breaking the results down further, Scherer said the team found a mutation that directly led to autism in one-quarter of the families studied.
In the other 25 per cent, Scherer said there is a mutation present and a child “may be autistic, may have Asperger’s syndrome, or you may not be autistic — in those cases we call them issues of genetic penetrance. We don’t know what is going on. It could be environment or other genes we haven’t figured out.”
Autism rates have skyrocketed in the past decade. Children with autism display a range of symptoms and behaviours. Some will be socially isolated, unable to look you in the eye or speak. Some have repetitive behaviours or targeted interests. Without early intervention therapy, these children can become trapped in their own minds, unable to care for themselves when they get older.
Whole genome sequencing is an important step forward in autism research, said Dr. Andy Shih, senior vice-president of scientific affairs at the U.S.-based Autism Speaks, and a study author.
“We have the tools, potentially, to really interrogate the genome and try to identify the risk factors that are genetically associated,” Shih said. “It will also give a foundation to try and understand what is really going on with the other 50 per cent that we are not seeing.”
If there is a genetically linked risk in half of the 32 cases, it does pose the question of what causes the other 50 per cent — raising the spectre of greater environmental influences.
“I think genes will always have a role in autism in some way. Do I think genes are always the cause? No,” said Scherer.
The finding should eventually lead to more accurate diagnostic testing and whole genome sequencing performed routinely to help diagnose autism. “When this paper comes out, I think it will open up the floodgates,” said Scherer.
Dr. Hakon Hakonarson, head of the Center for Applied Genomics at Children’s Hospital of Philadelphia, told The Canadian Press the research found “some new, novel variants that are likely to have a role in the pathogenesis of autism in these individual families.”
Hakonarson, who was not involved in the research, said the team had “identified some interesting genes, and at least some of them are very likely to be players and help certain families in the future.”