Modern eugenics will soon eliminate Down syndrome. (aka Down's syndrome in Canada and the UK)
If researchers come up with genetic tests for Asperger's, or even mere reading disorders, those disorders may also decline in frequency. I hope, however, that the abortion rate for dyslexia will be much less than 90%.
I don't really know what this will mean in the long run, but I don't think we'll be able to do a lot about it.
Update 11/30/08: A screening program in Denmark has cut the Downs syndrome birth rate by 50%.