The first time Bill heard the term “autism” applied to his little boy, “it felt like a curse word,” he said.
Yes, little Billy was slow to learn language and did not seem to engage with people. But autism? What was in store for him? Would he be able to live independently? Drive a car? Get a job? Marry?
And why? Why did his beautiful, 3-year-old toddler have this disorder, Bill, who asked that his last name not be used to protect Billy’s privacy, recalled wondering.
“I want to know what causes it,” he told Cathy Lord, a clinical psychologist and autism expert in a three-hours-long Zoom session from her office at the University of California, Los Angeles. Bill, in his apartment, told Dr. Lord that he had gotten a lot of suggestions from friends and relatives, and especially from social media.
His wife did not take Tylenol, but could it be red dyes in food that were the culprit? Or, as he saw on TikTok, a lack of vitamin B6?
“Do you think it has anything to do with vaccines?” he asked Dr. Lord. Billy is fully vaccinated.
For Dr. Lord, such questions are all too familiar.
Clinicians who treat autistic children must help their young patients’ families navigate a cacophony of theories and advice. As autism diagnoses have risen over the last decades and debate over its causes has intensified, they have been forced to explain to desperate parents the few knowns and the many unknowns about what leads to autism’s development.
Now that the federal government has entered the fray, often giving advice that doctors have to dispute, some families wonder whom they should believe.
Joseph Buxbaum, a neuroscientist who studies the genetics of autism, said families of autistic children that he has worked with for a decade or more are not sure what to think when they hear President Trump and Robert F. Kennedy Jr., the health secretary, talk about autism, blaming it on discredited theories like vaccines or unproven ones like acetaminophen, the active ingredient in Tylenol.
“Even people who trust us and know we disagree vehemently, it affects them,” Dr. Buxbaum, a professor at the Icahn School of Medicine at Mount Sinai, said. “It’s a shocking time.”
Decades of scientific research point most compellingly to genetic mutations affecting brain development as a primary driver of autism. Researchers have already identified hundreds of mutations linked to the disorder.
And while most scientists say genetics likely interacts in some way with environmental factors, research has disproved some of the most widespread notions and has produced weak or conflicting evidence for others.
Yet Mr. Kennedy, who has referred to the rise in autism cases as an “epidemic,” has been dismissive of genetics research, calling it a “dead end.”
“Genes don’t cause epidemics,” he said in the spring. “You need an environmental toxin.”
Like other parents, Bill said he had heard plenty about the rising incidence of autism, with cases increasing to one in 31 children from an estimated two to four children per 10,000 in 1980. He has to wonder, he told Dr. Lord, whether the soaring rate indicates that something in the environment is causing the disorder.
Not necessarily, Dr. Lord said.
“Mostly the numbers are bigger because the categories are so much larger now,” she said.
When she began studying autism 50 years ago, she told Bill, the disorder only included the most severe cases. Now there is an autism spectrum that includes people who have trouble reading social cues or making friends, as well as those who are severely disabled.
Awareness has also played a large role in the increased prevalence, Dr. Lord said, along with special services for children with an autism diagnosis and increased screening by pediatricians.
Assuaging Bill’s fears that maybe he or his wife did something to cause Billy’s autism, Dr. Lord pointed out that autism rates are similar in different countries, despite vastly different environments.
Dr. Lord and others who have spent decades studying autism tell their patients that the only consistent and well-documented explanation for autism is mutations in genes critical for brain development. But genetic mutations still only explain about 30 percent of cases, typically those with the most severe forms of the disorder.
The role of genes has been known about since the 1970s. Autism, studies found, was more likely to occur in identical twins than in fraternal twins, who do not share the same genetic makeup.
A landmark publication in 2007 showed that children with autism were much more likely to have so-called de novo mutations, spontaneous mutations that were not present in their mother’s or father’s genome. Such mutations often occur in the sperm or eggs even before a baby is conceived.
The more researchers looked, the more mutations — de novo and inherited — they found. In the most recent work, led by Dr. Buxbaum, an international consortium funded by the National Institutes of Health found, more than 250 different genes that, when disrupted, make profound autism extremely likely.
Different people may have different mutations within the same gene, but in every case, the mutations alter the gene’s function. Dr. Buxbaum’s colleague will present the work at next week’s meeting of the American Society of Human Genetics.
“These are not little flags in the genome that are pointing at some susceptibility,” Dr. Sebat, a geneticist at the University of California, San Diego and lead author of the 2007 study, said. “These are causal mutations.”
In contrast, studies have so far found only weak evidence for environmental factors — like pollution or certain chemicals — that might contribute to autism. They find correlations, but not causal evidence.
Some doctors are increasingly offering genetic testing to parents when their children are diagnosed.
Dr. Audrey Brumback, a pediatric neurologist at the University of Texas at Austin, said she offers genetic testing to most of the patients she diagnoses with autism even though, as she cautions the parents, a relevant genetic mutation will be found in only one out of four cases.
“Every mother that comes in the door is blaming herself because she had a half a glass of red wine in the second trimester, or took a Tylenol for one headache she had during pregnancy, or had a stressful experience during pregnancy,” Dr. Brumback said.
She explains that the chances of finding a de novo mutation go up if a patient has severe autism and other, co-occuring conditions, like epilepsy, movement disorders or an intellectual disability. For patients who receive negative results, she will often suggest getting retested in the future, in case scientists have discovered a new mutation that could be a match.
“Finding those answers for families — that in itself is therapeutic,” Dr. Brumback said. Sometimes a genetic diagnosis also helps unlock specific interventions that might help their kids, she added. “They’re searching for a specific condition based on the underlying cause, rather than consuming all of Facebook.”
When testing does find a related genetic mutation, some parents who have spent decades wondering why their child developed autism say they have found solace.
LeVar Baxter, a police officer who lives in Gerbersville, Pa. said that had been the case for him.
When his son, Khalil, was an infant, he hit his developmental milestones ahead of schedule. Mr. Baxter and his wife confidently predicted that Khalil would be walking by the time he was 9 months old.
But everything changed when Khalil was about 4 months old. He regressed, losing his developmental skills. Now 21, he is a seemingly happy young man who, Mr. Baxter said, smiles every day. But he does not talk, and he cannot live independently.
Mr. Baxter had not been able to put the worries out of his mind. Did he or his wife do something that brought on Khalil’s autism? Was it caused by something in the environment? Or, he wondered, could it be the vaccines his baby received?
“We know some people are allergic to milk or to peanuts,” he said. “Is it possible some people are allergic to vaccines?”
After seeing a notice that the Simons Foundation was seeking families who would be willing to provide samples for genetic research, Mr. Baxter decided he would do it.
“I wanted to know if I had a gene that I’d passed on to Khalil,” he said.
Ten years went by. Then, last year, he said, he got a letter from the Simons Foundation. They had found a gene.
Mr. Baxter was almost afraid to find out more. That notification, he said, “reset my anxiety.”
The mutation, he learned, is a rare one, CLCN4, associated with neurological development and speech.
“I couldn’t believe it,” Mr. Baxter said. “The first question I asked was, ‘Was there anything I did or that I could have done differently?’”
No, the counselor told him. Her analogy: Carmakers make a million cars a year. One of those cars will have engine troubles from Day 1.
“That took a major burden off my shoulders,” Mr. Baxter said. “For a long time, I had carried this guilt, letting doctors vaccinate him. I had blamed myself.”
At Dr. Lord’s suggestion, Bill, Billy’s father, also decided he wants genetic testing for his son. He knows that even if a mutation is found, there is not much he can do about it.
For now, Dr. Lord told him the good news is that Billy does not have severe autism. But the disappointing news is that she cannot predict what he will be like when he is older.
Bill was still sanguine.
“My wife says I’m a helicopter dad,” he said, adding, “Whatever I am, I will be there for him.”
Gina Kolata reports on diseases and treatments, how treatments are discovered and tested, and how they affect people.
Azeen Ghorayshi is a Times science reporter.
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