He doesn't mention suffering at all. He unambiguously makes the point that those with Downs do not contribute to society.
He makes a Tweet in reference to suffering according to the Telegraph, there's a print screen of the tweet. I've read the comment in regards to high-funcitoning autistics and have questioned you about evidence to the contrary above.
On the moral dilemma;
"Abort it and try again. It would be immoral to bring it into the world if you have the choice."
On why the same moral judgement doesn't apply to autism;
"People on that spectrum have a great deal to contribute, Maybe even an enhanced ability in some respects. DS not enhanced."
Dawkin's own written word. Couldn't really be any clearer.
What I'm asking you is what evidence is there to disprove Dawkins' statement in regards to individuals with DS not contributing?