Autism seems to me an umbrella term for what are probably a number of different conditions - the symptoms are so very different in different children - so I would expect causes to differ too. The MMR does not cause all cases of what is called autism, that's for sure. I have a close relative with an ASD diagnosis since 10, this person did not receive the MMR vaccine. I'm pretty sure the cause came in the womb - maybe a deficiency or deficiencies of nutrients, or a thyroid dysfunction, something like that. But so many parents reported a sudden collapse in their children after the MMR that it seems likely to me that it at least massively exacerbates existing conditions, perhaps in children with immune problems.