A massive international effort led by Canadian scientists has homed in on the genes behind autism - a breakthrough that could revolutionize how the mysterious and surprisingly common condition is both detected and treated.
Touting it as the most significant advance in the field in 30 years, researchers say the landmark project has put within reach a DNA test to identify children with autism early enough to counter the condition's worst effects.
"I don't think it's inconceivable that we're going to be able to prevent autism down the road," said study leader Peter Szatmari, director of the Offord Centre for Child Studies at McMaster Children's Hospital in Hamilton. "The clinical implications of this discovery are unprecedented."
Doctors currently rely on psychological tests to diagnose autism spectrum disorders in children at age 2 or 3. But a DNA test could identify those affected as babies, or perhaps even before they are born.
The findings, based on the largest autism DNA collection ever assembled, could also allow parents who have children with autism to learn through genetic screening their chances of having another affected child.
"If you know ahead [of time] of your predisposition to autism, you can make an informed decision," said Marie Jolicoeur, a Burlington, Ont., mother who has two sons with autism disorders and whose family contributed DNA to the project.
Using new genome scanning tools, researchers have found that several different autism-related genes can play a role in different families. This helps to explain why no two children - not even identical twins - have identical symptoms.
The researchers have pinpointed at least five areas of the genome that harbour genes linked to autism susceptibility, including those crucial for brain function. They have also found a genetic mutation tied to the disorder in girls - who are four times less likely than boys to develop autism disorders.
The work has also highlighted how autism can spring from genetic quirks not seen in either parent - suggesting that a genetic glitch has randomly emerged in the sperm or egg cells of the father or mother prior to conception.
Co-author Steve Scherer, senior scientist of genetics and genomic biology at Toronto's Hospital for Sick Children, said, "It may be that 5 to 10 per cent of autism cases are arising from these de novo [new] mutations."
The research, released yesterday in an advance online publication of the journal Nature Genetics, is the first part of a two-phase study run by the Autism Genome Project. It involves more than 137 researchers from 50 academic institutions in eight countries and the study of nearly 8,000 people from 1,600 families who have at least two members diagnosed with an ASD.
Dr. Szatmari, who set the ground rules for the unprecedented collaboration that began in 2002, said "the effort has meant the putting aside of individual ambitions to work together as a team."
Autism disorders have only recently been recognized as the most common serious developmental condition of childhood, affecting roughly one in 165 children. Experts refer to it as a spectrum because the complex neurological condition can range so widely in severity.
Some suffer severe cognitive impairment, others are savants. Many battle gastrointestinal problems and show a strong preference for strict routines and repetitive behaviours. But social deficits are its hallmark, impaired language, communication and the ability to interact with others.
Once considered rare, autism disorders seem to have risen dramatically over the last two decades. But Dr. Szatmari said many experts believe the increase can largely be explained by greater awareness, different diagnostic criteria and the specialized resources often made available to those with an ASD compared with another form of developmental condition.
Despite the growing awareness, autism's causes have stumped experts. Many suspect environmental triggers - prenatal hormones, toxins, food allergies and infections. But experts have long known genes play a major role. Autism disorders tend to run in families; if one identical twin has an ASD, there is a 65- to 92-per-cent chance the other will also develop the disorder. Doctors also see subtle forms of autism in parents that may not have been diagnosed.
