I have a good friend with Williams syndrome—one of the nicest and most caring people I know. He has extreme emotional swings, but unless I hadn’t been told by his parents, I’d never have realized he had any sort of diagnosable condition.
Much gets made of the “elfin” appearance, “cocktail party” personality, and “unusual verbal abilities,” but there’s nothing good about having Williams Syndrome.
I cringe at the use of language such as "nothing good about X" when talking about a population of people, as it reeks of ignorance. I will give you the benefit of the doubt though, perhaps you hadn't meant to come across so bald faced.