Such testing could also predict if parents with one autistic child are at greater risk of having another; if their child’s autism is linked to a spontaneous variation, they are at no greater risk than the general population. Researchers at Children’s Hospital, which provides genetic testing to families, are already developing a clinical diagnostic test.
Scientists are also trying to pinpoint the specific gene or genes within this section of DNA that underlie the increased risk. Daly and his collaborators plan to sequence this region of the genome in another group of people with autism, in search of single-letter mutations that might disrupt the function of specific genes. “Genetics provides us with the only opportunity to gain insight into the biological mechanisms that underlie autism,” says Daly. “We can look at individual gene discovery as a small first step in the overall path to develop treatments.”
Previous studies have identified autism risk genes. However, these studies have focused on people with genetic disorders that often co-occur with autism, such as Fragile-X syndrome, complicating the role those genes play in the disorder. “Up until now, we haven’t had the capacity to look at a single gene that is associated with pure autism,” says Gusella.
The findings could point to additional spots in the human genome to search for autism risk genes. The variation on chromosome 16 lies within a genetic “hot spot,” an area that is predisposed to undergoing structural duplications due to the architecture of the DNA, says Evan Eichler, a geneticist at the University of Washington in Seattle, who wrote an editorial accompanying the paper. “Every time we produce gametes, there’s a finite probability of this region to duplicate,” he says. In addition, the region has a high concentration of genes that are rapidly evolving in humans. While the significance of that finding is not yet clear, it may explain autism’s status as a relatively young disease.