RFK, Jr. Is Wrong about Cause of Rising Autism Rates, Scientists Say
Autism rates are rising, but RFK, Jr. is wrong about the reasons. Here’s what the science says
Research suggests that autism is between 60 and 90 percent heritable.
Robert F. Kennedy, Jr., head of the Department of Health and Human Services, struck an alarmist tone about new findings that one in 31 eight-year-olds in the U.S. have an autism diagnosis at a press conference today.
Kennedy called autism a “tragedy” that “destroys families.” And his statements also included assertations that autism experts say are out of date, such as the idea that autistic kids “regress” around their second birthday. In fact, while autism is often diagnosed at this age, researchers have found brain differences as early as six months of age among kids who were later diagnosed as autistic. Some studies have also found subtle differences in motor behavior and social behavior, such as looking less at people than typically developing kids do, in babies who were later diagnosed as autistic.
But Kennedy’s greatest breach with the scientific consensus was likely his insistence that autism is an “epidemic” that must be caused by an environmental exposure that has been introduced within the past several decades. In fact, researchers say, autism is between 60 and 90 percent heritable. And in up to 40% percent of cases, doctors can find a specific set of genetic mutations to explain the condition. While there are environmental risk factors for autism, such as air pollution, rising rates are mostly attributable to broadened diagnostic categories and more comprehensive screening.
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“The problem from a science communication standpoint is that the causes are complex,” says Annette Estes, director of the University of Washington Autism Center. “It’s not like Down syndrome, where we can say, ‘There is one genetic change that leads to this syndrome, and everybody with this syndrome has these characteristics.’ Even though the amount we’ve learned is unbelievable, it’s also not a simple story.”
The new finding that one in 31 kids born in 2014 are autistic comes from a newly released report from the Autism and Developmental Disabilities Monitoring Network (ADDM), which started tracking data in 2000. That year one in 150 eight-year-olds were diagnosed as autistic, and the number has been steadily rising since. Kennedy also cited numbers from the 1970s and 1980s that showed rates of autism that represented around one to three in 10,000 people.
This period saw a number of changes in how autism was diagnosed, however. The Diagnostic and Statistical Manual of Mental Disorders (DSM), which has lays out criteria for psychiatric diagnoses in the U.S., called autism “schizophrenic reaction, childhood type” in its first edition and subsequently referred to it as “schizophrenia, childhood type” until 1980, when the diagnosis changed to “infantile autism.” The criteria then focused on external symptoms such as delays in language development, resistance to change and attachments to objects. In 1987 the criteria widened and encompassed three categories related to social interaction, communication and restrictions in activities. In 1994 the diagnosis of Asperger’s disorder appeared, only to be subsumed into a broadened “autism spectrum disorder” in the DSM’s fifth edition (DSM-5) in 2013. That year was also the first in which autism and attention deficit hyperactivity disorder could be diagnosed in the same child at the same time, Estes says. Prior to that time, an ADHD diagnosis would preclude a child from getting an autism diagnosis, even though researchers currently estimate that half or more of autistic people also have ADHD.
Kennedy downplayed diagnostic shift as a minor explanation for the increase in autism cases, but researchers have found that changes in diagnosis probably explain a majority of the increase. A 2015 study on children diagnosed as autistic in Denmark, for example, found that 60 percent of the rise of autism among children born between 1980 and 1991 was caused by changes in diagnostic criteria and reporting practices. Another 2015 study examined students in U.S. special education programs between 2000 and 2010. The number of autistic children who enrolled in special education tripled from 93,624 to 419,647. In the same time frame, however, the number of children labeled as having an “intellectual disability” declined from 637,270 to 457,478. The shift of children from one diagnostic category to another explained two thirds of the increase in autism in this population, researchers say.
Another piece of evidence for changes in diagnosis explaining a large difference in the prevalence of autism is that autism rates vary widely from state to state in the U.S. The state with the highest prevalence of autism is California, with a rate of 53.1 per 1,000 eight-year-olds, while the one with the lowest prevalence is Texas, with a rate of 9.7 per 1,000 eight-year-olds. That’s a huge difference. But according to the CDC’s own report, it’s likely linked to California’s intense push for early screening and assessment.
“Because of all the hard work that everyone has done to come up with good approaches for supporting and teaching autistic kids, there are benefits of getting an autism diagnosis,” Estes says. “So people seek it out. And that, coupled with less stigma around autism, means more people want to understand their kids in this way.”
Some portion of the rise in autism rates may be unrelated to better diagnosis. The likelihood of having an autistic child increases for older parents, and there is a societal trend toward delaying childbirth across developed countries. Children who are born prematurely are also at a heightened risk of autism, and improved neonatal care means many more of these children are surviving to childhood and beyond.
There are also known environmental risk factors for autism. Among pregnant people, for example, infections that are accompanied by fever in the second trimester raise the risk of autism for their eventual baby. So does exposure to fine particulate matter pollution in the third trimester of development and the first year of life, according to a 2019 study. Laura McGuinn, an epidemiologist at the University of Chicago, who led a study that made the latter finding, says that particulate matter is inflammatory, and work is ongoing to understand how it might trigger the maternal immune system and potentially affect brain development.
As Secretary of Health and Human Services, Kennedy promised “some” of the answers to the causes of autism by September. But his “start from scratch” approach largely ignores research that has already been done. For example, Kennedy told reporters the initiative would look at ultrasounds during pregnancy as a possible risk factor. But a comprehensive multisite study of more than 1,500 pregnancies that found no link between autism and ultrasound use was published as recently as 2023. And scientists definitively ruled out the measles, mumps and rubella (MMR) vaccine as a cause of autism a decade ago (and again in 2019). In addition, the primary study that had suggested a link between the MMR vaccine and autism was found to have falsified data. Despite this, federal officials said in March that the Centers for Disease Control and Prevention will conduct a study to investigate a link between vaccines and autism. The study will be led by a vaccine skeptic who was previously disciplined for practicing medicine without a license.
Work on untangling the complex environmental risk factors was ongoing prior to Kennedy’s tenure, including at federal agencies such as the National Institute of Environmental Health Sciences, which is developing a Web-based tool to help scientists make sense of the existing data on environmental studies and autism.
“As scientists, I wish there was a way we could talk about this and really explain how amazing it is, how much taxpayer money has gone to creating this understanding of this complex developmental disorder and how to help kids and parents,” Estes says. “This idea that there needs to be one single cause, and it needs to be really scary—it’s just really taking us backward.”