Williams Syndrome is a rare genetic condition -- so rare, in fact, that few people have ever heard of it. Of about 7,500 newborns, only one will have it. But that one, should you ever meet him or her, will likely have a personality of unforgettable ebullience and warmth. It is the type of personality seen only occasionally beyond the world of Williams Syndrome.
Williams Syndrome is caused by the deletion of roughly 25 genes on chromosome 7. The deletion can occur randomly during the production of a sperm or egg cell. Though there are 20,000 to 25,000 genes in the human genome, even the loss of just 25 genes can have profound effects on a person's physical, behavioral and cognitive make-up.
Why the deletion of genes causes such friendliness and social disinhibition is not well understood. The development of our personalities is a complex relationship between our social environment and our genes -- both present and not.