What’s Really Behind the Recent Autism Increase?

Autism prevalence increase may be due to changing diagnoses

More US students are being diagnosed with autism than ever before, but is the disorder really on the rise?

Between 2000 and 2010, there was more than a three-fold increase in autism diagnoses among students in special education programs in the US.

Now researchers from Penn State University have found that this recent uptick in autism diagnoses may be, in large part, due to the reclassification of patients who previously would have been diagnosed with other intellectual disability disorders.

"For quite some time, researchers have been struggling to sort disorders into categories based on observable clinical features, but it gets complicated with autism because every individual can show a different combination of features" said lead study author Santhosh Girirajan, PhD, an assistant professor of molecular biology and anthropology at Penn State, in a press release.

Autism spectrum disorder (ASD) is a range of complex disorders that is characterized by social impairments, communication difficulties and repetitive behaviors.

The Centers for Disease Control and Prevention (CDC) estimates that 1 out of every 88 children age 8 will have ASD in 2015.

Using data from the US Individuals with Disabilities Education Act (IDEA), Dr. Girirajan and team looked at more than six million US children from 2000 to 2010.

Under the IDEA law, children are classified into 1 of 13 disability classifications. Only one of these categories can be used.

While autism diagnoses for children in special education classes tripled during this time, the total number of children in these classes remained stable.

As the number of autism diagnoses increased, diagnoses for other intellectual disabilities also decreased.

By the time these children reached age 15, reclassification accounted for 97 percent of the rise in autism diagnoses.

According to Dr. Girirajan and team, many other intellectual disabilities coexist with autism and may have similar symptoms.

"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," Dr. Girirajan said. "Every patient is different and must be treated as such.”

This study was published online in the July issue of the American Journal of Medical Genetics Part A.

Pennsylvania State University funded this research.

No conflicts of interest were disclosed.