Two major new studies grapple with the conundrum at the core of autism, the often-devastating disorder that can make it difficult for children to connect with their fellow humans. This news brings us two big steps further down the path of understanding this complex, enigmatic disease. And it reassures all parents that childhood vaccines do not appear to increase the risk of autism.
On Thursday, scientists reported that 1 percent of people with autism share a variation on chromosome 16. Several other genes have been previously implicated in autism, but this study in the New England Journal of Medicine is the first to find a consistent genetic variation in such large numbers of people. The researchers, led by the Boston-based Autism Consortium, scanned the dna of members of 751 affected families looking for shared clues.
"This finding really nails it," says Andrew Zimmerman, director of medical research at the Center for Autism and Related Disorders at the Kennedy Krieger Institute in Baltimore. He notes that the researchers triple-checked their work by also finding the same genetic anomaly in people tested at Children's Hospital Boston and in Iceland.
Until now, about 10 percent of autism cases have had a known cause, like Fragile X syndrome or congenital rubella. With this extra 1 percent now explained, that leaves another 89 percent to go. But autism is no longer the research backwater it was even a decade ago. Big guns in genetics, like Aravinda Chakravarti, an expert in the genetics of complex diseases at Johns Hopkins's Institute of Genetic Medicine, and Mark Daly, a statistical genetics guru at the Whitehead Institute for Biomedical Institute in Cambridge, Mass., signed on as coauthors of the NEJM paper.
"There have been very few diseases that have ever been treated without understanding their basis," says Eric Lander, a genomics pioneer and founding director of the Broad Institute in Cambridge, Mass., who was not involved in the study. This discovery is important for a reason that's not immediately obvious, he says. The implicated segment of chromosome 16 holds only about 25 genes. When researchers find the biochemical pathway used by the problematic genes in causing autism's symptoms, it will be easier to find other genes involved in what scientists have long recognized to be a dauntingly complex and varied disorder.
Even more interesting is the fact that the part of chromosome 16 that's been fingered as a culprit is notorious among geneticists for being young and unstable, an evolutionary hot spot that's shared by humans and other primates but not by older life forms. "I've always thought of autism as a uniquely human condition," says Zimmerman. What, indeed, is more human than the drive to communicate? Perhaps the recent evolution of our chattering species made us somehow more vulnerable to losing that gift.
The discovery doesn't help families who are currently struggling with autism, of course. But it does raise the possibility of developing a genetic test for markers like the chromosome 16 variation before too long. "We're less than a decade away from genetic testing for autism," says Peter Hotez, president of the Sabin Vaccine Institute and father of a 15-year-old daughter with autism. He, like many researchers, has despaired in recent years, as much energy has gone into battling over whether vaccines cause autism.
Earlier this week, researchers at the California Department of Public Health reported that the rates of autism in children born from 1989 through 2003 has risen, despite the fact that the preservative thimerosal, which contains toxic mercury, was largely phased out of vaccines during that time. It echoes studies in five other countries, including Canada in 2007, that failed to find a link between the use of vaccines or thimerosal and autism. Some parents and autism activists argue that vaccines, or the thimerosal in them, is responsible for autism. Hotez says: "It doesn't make sense that mercury would cause autism, because we know what mercury does cause"—horrible diseases like Minamata, in which children are born with deformed limbs. He's optimistic that the momentum for focusing on how genes interact with environmental triggers will soon bear fruit.