Williams syndrome is sometimes called the opposite of autism: people who have it tend to be extremely outgoing, socially uninhibited and driven to engage with everyone they meet. The tiny genetic deletion that causes Williams affects one in 10,000 people, or roughly 30,000 Americans. Journalist Jennifer Latson spent several years with one of them: Eli D’Angelo, whose story is chronicled in her new book, The Boy Who Loved Too Much, an excerpt of which is below.