Cases of autism, as the figures show, are on the rise, puzzling many as to why this developmental disorder now affects one in every 68 children.
Some believe the higher rates are related to vaccines, although studies show that is not the case. Other signs point to genetics and other factors.
But new research says the three-fold increase of autism cases is because of how diagnostic criteria has changed over the years.
The evidence, they say, is that children in special education classes are being diagnosed with autism more and other developmental disorders less.
In a new study published Wednesday in the American Journal of Medical Genetics, researchers at Penn State University examined 11 years of special education enrollment data, with an average of 6.2 million children per year.
While they observed no increase in children enrolled in special ed classes, they observed the rise in children diagnosed with autism coincided with an equal decrease in students diagnosed with other intellectual disabilities.
Lead researcher Santhosh Girirajan, an assistant professor of biochemistry and molecular biology at Penn State, said researchers have been struggling to sort developmental disorders into categories based on observable clinical features.
However, he said, it gets even more complicated with autism because every individual can show a different combination of features.
“The tricky part is how to deal with individuals who have multiple diagnoses because the set of features that define autism is commonly found in individuals with other cognitive or neurological deficits,” he said in a press release.
Autism Can Mean A Lot of Different Things
The latest figures from the U.S. Centers for Disease Control and Prevention (CDC) estimates that one out of every 68 children was diagnosed with autism in 2010.
Autism — medically known as autism spectrum disorder — envelopes a range of symptoms that impact a child’s social, communication, and behavioral abilities.
An autism diagnosis now means a child could have autistic disorder, pervasive developmental disorder not otherwise specified (PDD-NOS), or Asperger disorder, the CDC states.
As many of these symptoms overlap, such as emotional disturbances, it’s often difficult to pinpoint a single condition. The CDC estimates autism co-occurs with other chromosomal, developmental, genetic, neurologic, or psychiatric conditions up to 83 percent of the time.
Programs associated with the United States Individuals with Disabilities Education Act (IDEA) require children to be diagnosed with one out of 13 disability categories. These include autism, intellectual disability, emotional disturbances, specific learning disabilities, and other health impairments.
Reclassifying Percentage Is High
Using the data from the IDEA program, researchers noticed a three-fold increase of cases of autism from 2000 to 2010, but 65 percent of that increase could be caused by reclassification. The diagnostic reclassification of individuals from the category of intellectual disability to the category of autism accounts for a large proportion of the change, which varied depending on the age of the children.
The change varied depending on the age of the children, researchers noted. They estimate that 59 percent of the increase in autism diagnosis among 8-year-olds was due to reclassification. The same was true for as many as 97 percent of 15-year-olds.
Giriajan says because autism and other intellectual disabilities occur together so frequently they’re likely due to shared genetic factors in many neurodevelopmental disorders.
While diagnostic tools “lose specificity” when applied to people with different genetic disorders, future studies of autism prevalence should take into account detailed genetic analysis, Girirajan says.
“Because features of neurodevelopmental disorders co-occur at such a high rate and there is so much individual variation in autism, diagnosis is greatly complicated, which affects the perceived prevalence of autism and related disorders,” he said. “Every patient is different and must be treated as such.”
The research was funded by the Penn State Huck Institutes of the Life Sciences and the Penn State Department of Biochemistry and Molecular Biology.