This is what I found!
Existing research yet to identify a definitive cause for autism.
Just as autism is a spectrum, there is a spectrum of causes for autism as well. The cause of autism in one person differs from the cause of autism in another. Researchers are still trying to understand how genetic or environmental factors may play a role. The cause of autism could be due to a single gene, a collection of genes, a combination of genetic and environmental factors and so on and so forth. There is no known single cause for autism.
For a clearer explanation, refer to this video.
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