Williams Syndrome (WS) was discussed a while back on LW in the context of human enhancement.
I was fascinated to learn about WS. It's like the opposite of autism (or at least autistic savantism): good at social engagement, and bad at analytical thought.
I don't know if this, like autism, has varying degrees, but if it does, I've known at least one person far out on the scale.
I don't see how Williams Syndrome could be a spectrum, since it's caused by the deletion of specific genes; they're either there or they're not. I do recall one writer (perhaps Simon Baron-Cohen?) speculating that there may be a disorder spectrum opposite autism which has received little recognition because society is much more accommodating of people who're socially fluent but analytically inept than the reverse.
Link: abcnews.go.com/Health/friendly-extreme-meet-kids-adults-williams-syndrome/