He knows the difference between autism and Down's syndrome quite well. Earlier in the year he came out as supportive of those parents of autistic children who have long been agitating to continue to investigate a link between vaccinations and autism. I am not going to provide a link as you can easily google for it.

That is a very discredited view scientifically but there is still a very strong and active lobby of parents agitating for more attention to it politically. And every relative of an autistic child or even friends of families where there is one still has the angst of wondering why.
We know a bit about how and why Down's syndrome or cerebal palsy happens, but autism is still a mystery, with a lot of guilt and pain involved for the parents.

If I were cynical I might say he might have been thinking there that the diagnosis of autism is growing by leaps and bounds and that speaking about helping people with special needs children, you would get more bang for your buck and get a much larger group of people to think about voting for you than if you had used Down's syndrome as the example. What I am saying is that I think it was smart of him to bring autism up rather than just relying on everyone knowing about Sarah Palin's Down's Syndrome kid. Yes, he's pandering to the "growth" in autism, not that there's anything necessarily y wrong or insincere about it.