Also it clearly must be to some degree mutations if you believe the rates are going up, which even the government is no longer disputing (though that may not be conclusive proof, to me it seems evidence leans to more likely than not currently).
De novo mutations can also be caused by environmental factors, this is very well established and called "genotoxicity"[1] and certainly some people have been exposed to known genotoxic chemicals to varying degrees over time (formaldehyde) and who knows what undiscovered ones there are, newer standards of pesticide testing are starting to look for reproductive health effects but many chemicals that have been in use for a long time haven't been held to the highest standard.
Another reason you might think it would be "de novo" mutations is that this could be any sorts of random errors in the genome. If autism is an umbrella label for various genome errors (which it very well may be, since it correlates with other conditions very often), that may explain why it's so hard to pin down a few genes and why symptom expression varies so drastically.
Here's one: even if it were genetic, there could be triggering environmental factors that trigger the onset of autism (I'm just giving a hypothetical example, not making a claim here).
Autism is genetic but we cannot do genetic testing and prove that you have autism. Seems like a very circular reasoning.
Memory defaults can also cause segfaults.
EDIT: they have a FAQ about it: https://www.autism.org.uk/advice-and-guidance/about-autism/w...
Autism is also multiple things.
That may provide some insight about how there is not a "single `autism gene'" and how they hedged a bunch of these statements with "most" or "usually".
Maybe some day when we as a species understand brains better, some people will get a more precise label than "on the autism spectrum".
This rings true to me. As someone with an autistic loved one, I obviously think about it a lot.
If it were as simple as there being some simple genetic basis that gives you a single thing called autism, I would expect it, honestly, to have naturally died out long ago, just because it makes so many things harder for people that it cannot possibly have not had a disadvantage to reproduction.
I've also read ages ago in Scientific American that the difference between our brains and chimp brains is almost entirely in control DNA, not in genes. It matters a lot, but is often overlooked. (It used to be called "junk DNA", before people realised how important it was.)
> We don't fully understand how genes combine to make a person autistic.
EDIT: To add, if you get it slightly wrong... you're fine, it'll be adjusted for in next year's taxes.
[0] ...because it has to, in order to investigate evasion.
These are viable for the population as a whole, not just people with autism or identified learning difficulties.