Autism rates have tripled. Is it more common or are we better at diagnosing it?

Rates of autism among children in the New York and New Jersey metro area tripled from 2000 to 2016, according to a study published Thursday in the journal Pediatrics.

The authors, a team from Rutgers University, calculated the trend by analyzing the Centers for Disease Control and Prevention’s estimates of the number of children diagnosed with autism spectrum disorder by age 8.

Although there is no medical test for autism, the CDC has established a network of 17 sites across the country that estimate autism rates based on a combination of formal medical diagnoses and records from schools and health care providers.

According to a 2021 CDC report, the rise in autism rates nationwide was similar to the trend in New York and New Jersey. One in 54 children was diagnosed with autism at age 8 in 2016, compared to 1 in 150 in 2000.

Advances in diagnostic skills and greater understanding and awareness of autism spectrum disorders appear to be driving the increase, the Rutgers researchers said. But there is probably more to be said: Genetic factors, and perhaps some environmental factors, could also contribute to this trend.

Exactly what these other factors are is still unknown, but researchers are clear on at least one fact: Autism has nothing to do with vaccines.

“We’ve known for so many years that vaccines don’t cause autism,” said Santhosh Girirajan, an associate professor at Pennsylvania State University who studies the genetic basis of neurodevelopmental disorders and was not involved in the new study.

“On the other hand, we really don’t know: What are the real, definite environmental factors that you should avoid?”

The Rutgers study found that in New York and New Jersey, the proportion of 8-year-olds diagnosed with autism who do not have an intellectual disability has increased more than the proportion who have an intellectual disability — a five-fold increase 2000 to 2016 compared to a doubling.

That’s most likely because doctors are better at identifying cases of autism without intellectual disabilities — in other words, children with average or above average IQ who exhibit characteristics of autism, such as impaired social skills, repetitive behavior, and communication difficulties.

Such cases may be less obvious to parents, teachers, or physicians than cases in children with intellectual disabilities, who tend to have more difficulty completing daily tasks on their own and who are more likely to have difficulties in the classroom.

The new study also found that while racial disparities in autism diagnoses have narrowed, they persist. Historically, black and Hispanic children were less likely to be diagnosed with autism than white children. The new analysis showed that among children without intellectual disabilities, black children were 30% less likely than white children to be diagnosed with autism. However, the gap has narrowed for children with intellectual disabilities.

“A narrowing of differences has led to an increase in autism [rates]but that doesn’t mean the differences have disappeared,” said one author of the new study, Josephine Shenouda, an epidemiologist at Rutgers.

Shenouda and her team recommended that all young children be screened for autism during routine checkups with their pediatricians, echoing the guidance of the American Academy of Pediatrics.

“Many major pediatricians in most major territories will conduct universal screening as part of their developmental surveillance of children during their childhood visits. However, this does not happen consistently, and even when it does, the follow-through – where parents are referred to appropriate services – is also missing,” she said.

She estimates that half of the children in the US are screened for autism.

Megan Krail
Megan Krail works with a boy with autism at the Callier Center for Communication Disorders at the University of Texas at Dallas in 2016.LM Otero / AP file

But more children being screened and broader criteria for diagnosing autism also create more opportunities for misdiagnosis, Girirajan said. That could further contribute to the rising rates.

“You might see a child and not be able to tell if it’s ADHD or autism or just a mild intellectual disability. And what happens is that you have to use more standardized tests to consistently identify children with similar characteristics. ” he said.

Aside from improvements in diagnostics, genetic factors could themselves be driving up cases of autism, experts said.

Much of the risk of developing autism – around 83% according to one analysis – stems from inherited genetic factors. Girirajan estimated that 2,000 to 3,000 genes contribute to autism, although only 100 are consistently associated with the disorder.

A child can inherit risk factors from one or both parents, and older parents are at greater risk of having children with autism.

“We’re seeing trends over time in parents waiting to have children, so some of the increase could certainly be explained by the age of the parents,” said Jennifer Durocher, clinical associate professor of psychology at the University of Miami.

Girirajan said environmental factors, such as exposure to air pollution, are unlikely to be major contributors, but they could exacerbate underlying genetic risks.

A 2021 study suggested that childhood viral infections could also be a risk factor for autism in boys, while other studies have pointed to links between autism and vitamin D deficiency, gut inflammation, and exposure to toxic chemicals.

“These are novel, emerging concepts,” Girirajan said. “We don’t have solid evidence that these actually cause autism.”

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