Scientists have discovered a pair of genetic mutations that markedly boost a child's risk of autism, researchers report Thursday.
The mutations — missing or duplicated snippets of DNA on chromosome 16 — may raise a child's risk of autism 100-fold, the study says. Although the genetic errors occur in just 1% of autism cases, that amounts to a lot of children.
"There are probably a million kids in this country with autism. About 10,000 of them have this mutation," says David Miller of Children's Hospital Boston, where a diagnostic test was developed and is available.
The research marks a major turning point. Scientists no longer are simply describing the many facets of autism but are probing its biological roots.
Previous studies show 90% of cases result from genetic abnormalities, but those found so far explain autism-related disorders in only 10% of patients.
The newly discovered genetic errors occur before fertilization, Miller says, a finding that bolsters the belief that autism-related disorders are genetic or developmental, not caused later in life by childhood vaccinations.
Researchers at the California Department of Public Health on Monday further weakened the vaccine-autism connection. They reported that autism rates in California have continued to climb, from three per 1,000 in 2003 to four per 1,000 in 2007, even though the preservative thimerosal, which has been widely blamed for autism, was banished from almost all vaccines by 2001.
In the new study, researchers for the first time scanned the entire genetic code of 1,441 children with autism or a related disorder and a similar number of parents whose DNA is stored at the Autism Genetic Resource Exchange. They also scanned the DNA of almost 1,000 patients from Children's Hospital Boston and another 18,000 control subjects from Iceland whose DNA was analyzed by the firm DeCode.
Researchers found 13 children who were missing snippets of DNA and 11 who had duplications. In all the cases, the children had autism or related problems, the researchers report in today's New England Journal of Medicine.
"This might be the tip of the iceberg" of dozens of genetic errors, says Andrew Zimmerman of the Kennedy Krieger Institute Center for Autism in Baltimore. Finding more, he says, would enable researchers to create genetic arrays, much like computer chips, that could be used as a one-shot test for many forms of autism.
"If we can identify children at risk for autism very early, we have the chance to intervene early while the brain is still developing," says Annette Estes of the University of Washington's Autism Center Research Program.
Jean Yates of Pound Ridge, N.Y., the mother of two boys with autism, 13 and 17, was elated to hear her family's involvement in the exchange consortium may have made a difference to other families grappling with autism. "I wanted very badly to help," she says. "We gave so much of our blood."