When President-elect Donald J. Trump pondered in a recent television interview whether vaccines cause autism — a theory that has been refuted by dozens of scientific studies — autism researchers across the country sighed in frustration.
But during his interview on NBC’s “Meet the Press,” Trump made a passing comment that everyone agreed with: “I mean, there’s something going on,” referring to rising rates of autism. “I think someone has to find out.”
Writer Emily Baumgartner asked, in an article in the New York Times, What is happening? There is no doubt that autism diagnoses are on the rise in the United States. According to data collected by the Centers for Disease Control and Prevention from 11 states, about 1 in 36 children suffer from autism, compared to 1 in 150 children in the year 2000, and researchers have not yet reached a conclusion. Clear explanation. They attribute much of this rise to increased awareness of the disorder and changes in how medical professionals classify it. But scientists say other factors, genetic and environmental, may also play a role.
Autism spectrum disorder, as it is officially called, is broad in nature, characterized by a combination of social and communication issues and repetitive behaviors and thinking patterns that vary in severity. A child with mild autism may have difficulty processing social cues, while a child with a severe condition may be unable to speak. There is no blood test or brain scan to determine who has autism, only a doctor’s notes.
Since there is no single cause for autism, scientists say there is therefore no single driver behind the rise in cases.
But at the heart of the question is an important distinction: Are there more people showing autistic traits, or are more people with such traits being identified now? Both appear to be true, but researchers aren’t really sure.
Here’s what they know:
An elusive reason
More than 100 genes have been linked to autism, but the disorder appears to result from a complex mix of genetic predispositions and environmental triggers.
The Centers for Disease Control and Prevention, Medical News Today, conducted a large-scale study of risk factors that can contribute to autism. Researchers examined dozens of potential triggers, including pollution, exposure to toxic chemicals and viral infections during pregnancy.
Some research suggests that children born to older fathers – especially older fathers – may be more likely to develop autism. Other studies suggest that premature birth or low birth weight may be linked to autism, which is often linked to high oxidative stress.
The idea that such factors may also be involved in the general rise in autism is compelling to Jurgen Hahn, a professor at Rensselaer Polytechnic Institute who studies the computational biology of autism, given that the number of babies surviving premature birth and the average age of new parents is on the rise.
But a hypothetical motor test for autism means controlling for the endless list of other influences on early development and following the child into adulthood, when some people now receive their diagnosis.
“These are very complex studies to do, especially if you want statistical certainty, and there are no easy answers,” Dr. Hahn said. “Sometimes we just have to say we don’t know. That always gives people room for speculation.”
The misleading theory that vaccines are the cause of this disorder is one case of speculation. This theory gained momentum when a British researcher named Andrew Wakefield published a study conducted on 12 children in the late 1990s, claiming that it revealed a link between the measles, mumps, and rubella vaccine and autism. Since then, several larger studies have refuted this hypothesis, including a study that included the entire population of children in Denmark. Aside from the types of vaccines, ingredients, or timing of the schedule, researchers have been unable to prove a link. Dr. Wakefield’s article was retracted, and his medical license was revoked, but the seeds had been planted in social discourse.
Diagnostic changes
One component of the autism boom is more certain: the expansion of spectrum criteria. Symptoms of autism first appeared in the Diagnostic and Statistical Manual of Mental Disorders in 1980, in the third edition of the manual, but its definition was changed in 1987, when it came to include children whose symptoms appeared at ages older than 30 months. The new edition also expanded the criteria for diagnosing autism from 6 to 16, and said that children need to show only half of the 16 criteria listed, instead of all 6 of the previous criteria.
The fourth edition of the Diagnostic and Statistical Manual of Mental Disorders, published in 1997, included Asperger’s syndrome, a social disorder characterized by a preoccupation with one’s interests, on the autism spectrum. This was a major shift, because it meant that all people – including those with average or even above average intellectual abilities – could receive the diagnosis.
The fifth edition, released in 2013, allowed clinicians to give a combined diagnosis of autism spectrum disorder and attention-deficit hyperactivity disorder. It also brought autism, Asperger syndrome and a condition called PDD-NOS — short for pervasive developmental disorder, not otherwise specified — under one umbrella.
“What we call autism has changed to become a broader category,” said Simon Baron-Cohen, director of the Center for Autism Research at the University of Cambridge. With “the growth in private clinicians providing diagnostics — it’s become an industry,” he said.
As these clinical processes evolved, the social infrastructure also evolved. Until the 1980s, many people with autism were institutionalized, so parents were less familiar with the distinctive features of the disorder and usually did not recognize it or seek a diagnosis when it occurred in their children.
Then in 1991, children diagnosed with autism began to qualify for special services in schools, giving parents an incentive to seek out and accept diagnoses. In 2007, the American Academy of Pediatrics recommended that all children be screened for autism between 18 and 24 months, which experts believe has led to a significant increase in detection.
Several changes in population-level trends add further evidence that awareness and inclusion may be behind this rise. Historically, boys have been diagnosed with autism at much higher rates than girls, who are believed to “hide” their autism symptoms due to social norms.
In conclusion, vaccines do not cause autism, and we are still trying to find out its causes.