Another Nail in the Coffin...
In their study - "A unified genetic theory for sporadic and inherited autism." - the authors describe exactly how spontaneous mutations could cause both sporadic autism (autism in families without a family history of autism) and familial or inherited autism.
You see, this has been the real mystery in autism (not the faux myteries of "poor excretion" and "mercury poisoning") - how families with inherited autism can show the same mutation in all affected members yet not have the same mutation as other families with inherited autism (for example, see here, here, here, here and here).
The answer, it appears, is that females with mutations associated with autism may be resistant to developing autism. Why this is so is not yet clear, but it has been shown pretty conclusively. These women may have one of the many mutations that cause autism but they do not develop the disorder themselves.
However, even those who don't develop autism are still carriers of that genetic mutation and (on average) 50% of their sons will receive that the mutation. Of the sons receiving the mutation, a high percentage of will develop autism. Additionally, about 50% of their daughters will also get the mutation, although only a few will develop autism (all who receive the mutation will be carriers).
This, of course, is not the entire story, but it is a reasonable lay summary of the article.
For those people who will immediately say, "Aha! It's those nasty chemicals/viruses/cell phones that are causing mutations in our children!", let me point out one thing:
The mutations are in the germ cells (i.e. sperm and eggs) of the parents of the autistic children. For these mutations to happen in a child and cause autism, it would have to happen at the single-cell stage (immediately after fertilization).
I encourage people to read the article for themselves - it's available free online. Don't just take my word for it. It's not an easy read, but even if you can't understand it all, you should come away with the idea that [a] this looks less and less like a simple case of "environmental toxicity" and [b] it is a much more complex issue than many of the autism "advocates" would have you believe.