Chromosome abnormalities are an intense interest of mine, so I have definitely heard of Williams Syndrome!
There do seem to be a subset of people with WS who are typically autistic, but the majority show a mix of very high sociability and good facial recognition combined with poor social skills.
Other traits include musical talents and love of music, auditory hypersensitivity, ADHD symptoms, anxiety and phobias, very poor spatial and math skills and expressive language strengths (often with expressive language better than receptive language, an unusual profile in developmental disabilities). Most people with WS have a below-average IQ, but come across as smarter than they are because of their verbal strengths.
There are also physical features such as a distinctive 'elf-like' facial appearance, short stature, heart problems such as aortic stenosis and high calcium levels.
These are all features of the 'typical' deletion size, but there are also atypical deletions, which are smaller. Depending on which genes are included in the deletion, they will have different pieces of the phenotype. For example, the expressive language strengths and spatial impairment have been linked to one gene, the lower average IQ to another, and the aortic stenosis to a third gene. They're still mapping out which genes the other traits are associated with. My impression is that the atypical deletions may be more strongly associated with autism than the typical deletion, because the person could end up with poor social skills without the hypersociability if those map to different genes. I've also heard of shyness being a feature of some people with atypical deletions, probably because they got the increased anxiety without the hypersociability that counteracts the effects of anxiety in social situations.
