New cases of autism spectrum disorder (ASD) are on the rise in the New York/New Jersey metro area, and it may be due to the fact that children without co-existing intellectual disabilities are being diagnosed at a higher rate.

Autism rates increased by as much as 500 percent between 2000 and 2016 according to the Rutgers study. The highest increase was among kids without intellectual disabilities. In the past, studies suggested that autism typically co-occurs with intellectual disabilities.

“One of the assumptions about ASD is that it occurs alongside intellectual disabilities,” said Josephine Shenouda, an adjunct professor at the Rutgers School of Public Health and lead author of the study published in the journal Pediatrics. “This claim was supported by older studies suggesting that up to 75 percent of children with autism also have intellectual disability.”
“What our paper shows is that this assumption is not true,” Shenouda said. “In fact, in this study, two-in-three children with autism had no intellectual disability whatsoever.”
For the study, researchers used data from the New Jersey Autism Study to identify 4,661 8-year-olds with ASD in four New Jersey counties (Essex, Hudson, Ocean and Union). Of these, 1,505 (32.3 percent) had an intellectual disability; 2,764 (59.3 percent) did not.
Rates of ASD co-occurring with intellectual disability increased two-fold between 2000 and 2016 while rates of ASD with no intellectual disability jumped five-fold, from 3.8 per 1,000 to 18.9 per 1,000. While better testing and more awareness of ASD may play a role in the findings, it could also be that kids without intellectual disabilities were previously falling through the cracks.
The Rutgers study also showed that Black children with ASD and no intellectual disabilities were more likely to be underdiagnosed. This goes along with previous findings that diagnosis can be affected by race and socioeconomic status. Shenouda said that hopefully these new findings will help close the gap and bring more services to lower-income areas where they are needed.
“With up to 72 percent of the ASD population having borderline or average intellectual ability, emphasis should be placed on early screening, early identification and early intervention,” she said. “Because gains in intellectual functioning are proportionate with intense intervention at younger ages, it’s essential that universal screening is in place, especially in underserved communities.”
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