“One of the assumptions about ASD is that it co-occurs with intellectual disabilities,” said Josephine Shenouda, assistant professor at 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 75 percent of autistic children also have intellectual disabilities.”
“Our paper shows that this assumption is not true,” Shenouda said. “In fact, two out of three children with autism in this study had no intellectual disability.”
Additional Testing Needed
Using biennial data from the New Jersey Autism Study, researchers identified 4,661 8-year-olds with ASD in four New Jersey counties (Essex, Hudson, Ocean, and Union) during the study period. 1505 of them (32.3 percent) had mental disabilities; 2764 people (59.3 percent) did not do it.
Subsequent analysis revealed that Rates of ASD with intellectual disability doubled between 2000 and 2016 – From 2.9 per 1000 to 7.3 per 1000. Rates of ASD without intellectual disability increased fivefold, from 3.8 to 18.9 per 1,000.
Shenouda said there may be explanations for the observed increases, although more research is needed to determine the exact causes.
“Better awareness of ASD and testing play a role,” said Walter Zahorodny, an associate professor at Rutgers New Jersey School of Medicine and lead author of the study. “But the fact that we’re seeing a 500 percent increase in autism among kids with no intellectual disability—the kids we know are falling through the cracks—suggests that something else is driving the increase.”
Early intervention is critical for children with ASD
ASD prevalence is associated with race and socioeconomic status. A Rutgers study found that Black children with ASD and no intellectual disability were found to be 30 percent less likely than white children. children living in affluent areas were 80 percent more likely to be identified with ASD compared to children in areas with no intellectual disabilities.
Using data from the New Jersey Autism Study and US Census data, the researchers were able to estimate rates of ASD underreporting in four states. Eliminating the findings could help close identification gaps and ultimately bring much-needed ASD services to low-income areas, Shenouda said.
“With up to 72 percent of the ASD population having borderline or average intellectual ability, the focus should be on early screening, early identification and early intervention,” he said. “Because gains in intellectual functioning are proportional to intensive intervention at a young age, universal screening is important, especially in underserved communities.”