The percentage of American children believed to have autism has jumped 30 percent in two years, according to new data released Thursday by the Centers for Disease Control and Prevention, which found that 1 in 68 children met the criteria for autism spectrum disorder in 2010 – up from 1 in 88 children in 2008.
The latest CDC estimates mean autism could be more than twice as common as officials said it was just seven years go, affecting about 1.2 million U.S. children and teens.
But health officials note that the new numbers may not mean autism is occurring more often. Much of the increase is believed to come from a cultural and medical shift as doctors diagnose autism more frequently, especially in children with milder problems.
There are no blood or biological tests for autism, so diagnosis is not an exact science. The condition is identified by analyzing a child’s behavior.
The CDC report released Thursday is among the most comprehensive studies available on the frequency of autism. Researchers gathered data in 2010 from areas in 11 states — Alabama, Arizona, Arkansas, Colorado, Georgia, Maryland, Missouri, New Jersey, North Carolina, Utah and Wisconsin.
The report focused on 8-year-olds because most autism is diagnosed by that age. The researchers checked health and school records to determine which children met the criteria for autism, even if they had not been formally diagnosed. Then, the researchers calculated how common autism was in each location and nationwide.
The CDC started using this method in 2007 when it came up with an estimate that 1 in 150 children had autism. Two years later, the estimate increased to 1 in 110.
For decades, the diagnosis of autism was made in children with severe language, intellectual and social impairments, as well as unusual repetitious behaviors. But the definition has gradually expanded and now includes milder, related conditions.
The latest CDC numbers come just days after a new study suggested that autism may be detectable before birth, a finding that could bring researchers closer to diagnosing the disorder earlier.
The study, published Monday in the New England Journal of Medicine, found that changes causing autism likely happen while a child is still in the womb.
Researchers looked at the post-mortem brain tissues of eleven children who had autism. They specifically examined an area of the brain known as the prefrontal cortex, a thin sheet of nervous tissue that's critical for memory and learning, which develops during the second trimester of pregnancy.
While looking at this area of the brain, scientists discovered disorganized patches consisting of undeveloped cells, explaining the wide range of symptoms seen in children. The same tissue samples from children without autism didn't share these characteristic patches.
The patches occurred in regions that control emotion, communication, language and social comprehension, all functions impaired in autism, the researchers wrote.
The Associated Press. Amel Ahmed contributed to this report.