Myth 5: Autism is on the rise and is strongly affected by environmental influence.
Researchers believe that autism itself is not increasing in rapid numbers, but diagnoses are, owing to better methods of diagnosing autism. Much of autism is more and more being linked to genetics, Wang said.
Stress, particularly in the mother’s second and third trimester, can affect the brain during early development.
For instance, autism is more likely in mothers who had to flee a hurricane or go without shelter or basic necessities during an ice storm, Wang said.
“The recognized rate of autism is going up, but in fact, it is quite possible that the characteristics of children have not changed in the last 20 years,” Wang said, referring to the belief that autism rates are not rising so much as doctors’ ability to diagnose autism is improving.
The relative risk for autism is roughly 1 in 100. Having older parents increases the risk a bit, but other things, such as emigrating while pregnant and fleeing a hurricane, increase the risk much more—2 times more likely and 3 times more likely, respectively.
A child born more than 6 weeks premature is 7 times more likely to be diagnosed with autism, and a child who receives no social attention or interaction in an orphanage is 8 times more likely to land on the autism spectrum.
“Relative to all these risks, the risk of genetics is enormous,” Wang said.
Sharing half of your DNA with a fraternal twin increases your own likelihood for autism 22 times, and having an identical twin on the autism spectrum makes you 84 times more likely to be diagnosed with autism.
“Autism is a really interesting example about there being an interplay between genes and environment,” Wang said. “It may be a case of bad input to the developing cerebral cortex—the front part of the brain.”
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