Outside of specific genetic diseases, scientists have identified more than 250 genes that are associated with a higher likelihood of ASD. As Maureen Durkin, a professor at the University of Wisconsin-Madison, explained to me, some of these genes are also associated with beneficial traits. “It’s not as simple as ‘these are causes of autism, and you’d want to edit them out of the genome,’” she said.
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Data from around the world support expanded diagnosis as the key factor behind climbing autism rates. A study in Denmark, published in JAMA, attributed 60 percent of ASD’s increase to broadened criteria and better reporting. A study in Canada concluded that 33 percent of the increase was due to diagnoses switching from another condition. Fombonne noted that similar trends are seen in every country. “The fact that it happened everywhere at the same time is not suggestive of something happening in the environment,” he said.
The CDC’s reports support the expanded diagnosis theory as well. Before 2016, the highest ASD prevalence was among White children and kids from areas of higher socioeconomic status. As screening improved, disparities decreased; in 2020, higher prevalence was seen in Black and Hispanic children and the association with household income faded.
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Are there any potential biological reasons for increasing autism rates? The experts I spoke to have differing views. Laurent Mottron, a University of Montreal psychiatrist and researcher, believes the number of people profoundly impacted by autism — what he calls “prototypical autism” — has not increased. Others, like Mandell and Durkin, said it’s possible that factors such as advancing parental age and better medical care that improves survival rates for premature infants could be contributing to the increase.