A furious debate over autism's causes leaves US parents grasping for answers

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?

- Gina Kolata and Azeen Ghorayshi

And why? Why did his beautiful, three-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 clinical psychologist and autism expert Cathy Lord in a three-hour Zoom session from her office at UCLA.

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 children with autism 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.

Dr Joseph Buxbaum, a neuroscientist who studies the genetics of autism, said families of children with the condition that he has worked with for a decade or more are not sure what to think when they hear American President Donald Trump and Mr 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," said Dr Buxbaum, a professor at the Icahn School of Medicine at Mount Sinai. "It's a shocking time."

ROLE OF GENETIC MUTATIONS