Genes and the microbiome are some of the most promising leads.
The strongest evidence of a cause: genetics
Autism spectrum disorder is a collection of close to 1,000 different conditions, with symptoms ranging from delayed speech development to asocial behavior and repetitive movements.
But “of all the causes of autism, the thing we know with the greatest certainty is that it’s a very genetic disorder,” said UCSF geneticist and autism researcher Stephan Sanders. “If you look at a child with autism, then look at their siblings, you’ll find the rate of autism is 10 times higher in those siblings than in the general population. This has been looked at in populations of millions.”
Exposure to infections and certain medicines during pregnancy may be linked to autism
Not everyone with those genetic mutations has autism — and that’s because researchers believe it’s not mutations alone that cause the disorder.
In many cases, you need that underlying genetic predisposition or mutation to collide with a range of potential environmental triggers. And finding those environmental risk factors is where things get murky pretty quickly.
Researchers have proposed dozens of potential environmental contributors to autism — including air pollution, pesticides, antidepressants, and viruses. And few of them have very robust science behind them, in large part because it’s much trickier to confirm the environmental causes of a disease.