No, you would not have a case, because 1) the doctor did not cause the Down's Syndrome; 2) there is nothing that could have been done to have prevented or cured the Down's Syndrome; 3) the only thing you could have done would have been to abort the child--but I do not believe that a court would give you compensation for not having aborted, on public policy grounds (i.e. if there is compensation for not aborting children with developmental syndromes or difficulties, that is getting close to endorsing eugenics); and 4) in any event assuming you discovered the Down's Syndrome more than a year ago, it would be too late under the statute of limitations for your state.