The recent claims of rise in autism rates was due to reclassification of people with related neurodevelopment disorders, say researchers at the Pennsylvania State University.
According to a recent report by the US Centers for Disease Control and Prevention (CDC), the prevalence of autism has increased from one in 5,000 in 1975 to one in 68 in 2012. The rate has increased from 6 percent to 15 percent each year from 2002 to 2010.
"If you asked me, 'Is there a real increase in the prevalence of autism?' maybe there is, but probably much lower than the reported magnitude," said lead researcher Santhosh Girirajan.
The researchers analyzed medical data of approximately 6.2 million school children in the US diagnosed with disabilities, enrolled in special education programs between 2000 and 2010.
Based on the diagnosis, each child was assigned to one of the 13 categories of disability, one of which was autism.
The analysis showed that between 2000 and 2010 the number of children diagnosed with autism more than tripled from 93,624 to 419,647. The additional rate includes the children who were originally diagnosed with "intellectual disability."
Girirajan said that the autism rise was partly down to students being reclassified from one category to another.
"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," he explained.
The rise has been linked to an increased awareness of autism and a broadening of the diagnostic criteria for the condition.
The study is evidence that a significant portion of that increase may be a result of the reclassification of individuals with related or similar neurodevelopmental disorders rather than an actual increase in the number of new cases of autism.