Here's a list of sypmtoms from the syndrome. Like BPD, many may have some but not all. But just having one or two doesnt mean you have it.

• Delayed speech that may later turn into strong speaking ability and strong learning by hearing

• Developmental delay

• Easily distracted, attention deficit disorder (ADD)

Feeding problems including colic, reflux, and vomiting
Inward bend of the small finger (clinodactyly)

• Learning disorders

• Mild to moderate mental retardation

• Personality traits including being very friendly, trusting strangers, fearing loud sounds or physical contact, and being interested in music

• Short compared to the rest of the person's family

Children with WS are overly social and outgoing, inappropriately friendly to adults and unwary of strangers. They are usually talkative, with intense enthusiasm bordering on obsession for topics that interest them.
Throughout childhood, the child with Williams syndrome may exhibit deficits in the ability to reason and in self-help skills.

and a lot more (this is a list that i have made up for my mom to read).