Some believe the higher rates are related to vaccines, although studies show that is not the case.
Advertisement
There are some risk factors that might account for a small amount of the increase in autism cases, says Jon Baio, a Centers for Disease Control and Prevention (CDC) epidemiologist and principal investigator for an autism monitoring program.
Here’s how that works: In 1975, physicians examined thousands of children every year who exhibited signs of autism-the sort of symptoms on the autism spectrum that any modern doctor would flag accordingly. Children who were more likely to be classified with other intellectual disabilities in the past are more likely to be called “autistic” today, making it look like more children have autism.
So in a new study, researchers mapped out the number of children who benefitted from special education between 2000 and 2010, and found that, while the number of special needs children remained constant over that decade, the number of children diagnosed with autism rose by a factor of five.
Santhosh Girirajan, an assistant professor of biochemistry and molecular biology and of anthropology at Penn State and colleagues looked at 11 years of special-education enrollment data covering more than 6 million children a year. For example, he says, there are now more autism cases with milder symptoms, such as normal or above-normal intellectual ability. In a press release, Girirajan explained, “When individuals carrying classically-defined genetic syndromes were evaluated for features of autism, a high frequency of autism was observed, even among disorders not previously associated with autism, suggesting that the tools for diagnosing autism lose specificity when applied to individuals severely affected by other genetic syndromes”. The CDC estimates autism co-occurs with other chromosomal, developmental, genetic, neurologic, or psychiatric conditions up to 83 percent of the time. This increase is potentially due to a diagnostic reclassification from frequently comorbid features such as intellectual disability, according to researchers. Yet almost two-thirds of that increase was matched by a decline in the rate at which children were labeled as having an “intellectual disability”. They estimate that 59 percent of the increase in autism diagnosis among 8-year-olds was due to reclassification.
The change varied depending on the age of the children, researchers noted. But the reasons may be far more benign than the latest conspiracy theory would suggest, according to a new study in the American Journal of Medical Genetics.
“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”, said Girirajan. “Standardized diagnostic measures incorporating detailed genetic analysis and periodic follow up should be taken into account in future studies of autism prevalence”.
Advertisement
The research was funded by the Penn State Huck Institutes of the Life Sciences and the Penn State Department of Biochemistry and Molecular Biology.
