June 9, 2011 -- 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.
When 20/20's Chris Cuomo attended a camp for children with Williams he was besieged by hugs and slaps on the back. Then came the barrage of questions. "What's your favorite color?" "Where do you live?" "Have you met Barney the Dinosaur?"
Children with Williams are also often identifiable by a variety of facial characteristics, from small, pointed teeth, to upturned noses, to a telltale puffiness under their eyes. But the camp is a place where everybody wants to be your friend regardless of who you are or what you look like.
"Little babies will come up to you, they will stare into your face, and it will be hard to actually disengage from that stare," explained Helen Tager-Flusberg whose lab at Boston University studies the social behavior of children with Williams. "When they're four or five...whether they know you or not, within about five minutes you're their new best friend."
One fascinating study by researchers in Europe found that children with Williams show no racial bias whatsoever. While children, even babies, prefer people of their own race, the neural pathway that imprints for race bias is somehow lacking in children with Williams.
What Causes 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.
If you think most children -- with or without Williams -- are warm and open, you'd be wrong. Tager-Flusberg's research team has recorded hours of video comparing children with Williams to typically-developing children.
In one experiment to test empathy, the adult experimenter bangs her knee on a table and expresses a great deal of pain. In many runs the lab recorded, the typically-developing child just watched and expressed no empathy or concern. But children with Williams often went right over to the experimenter to rub her knee and ask, "What's wrong?"
With such empathy comes a lack of fear. Watching a recording of a typically-developing child reacting to a hairy, moving, toy spider, Tager-Flusberg noted, not surprisingly, "She doesn't want to approach it...and doesn't have any inclination to go near to it and touch."
What do most children with Williams Syndrome do when presented with the creepy spider? They pet it.
But this lack of fear has a scary side, too. In another experiment, Tager-Flusberg has a stranger enter a room. And not just any stranger, but one wearing a baseball cap and dark sunglasses. As you would guess, children without Williams avoid the stranger like the plague. Children with Williams, however, often engage the stranger in conversation, and in one case we saw a child even offered a toy for the stranger to play with.
Such social disinhibition and innocence can have real-life consequences, and that extends to adults with Williams Syndrome.
Kelley Martin, 34, of Westwood, N.J., has Williams Syndrome; she was bullied by a so-called friend into paying for that friend's expenses. Kelley's mother, Anne, realized what was happening $1,500 later.
"It's very scary," Anne Martin told 20/20. "Because I know what can happen to her if there's nobody watching for her."
Friendliness and fearlessness aside, people with Williams often have a number of physical ailments, including serious heart conditions. Such conditions cause many adults with Williams to survive only into their 50s.
Michelle Self's son, Alex, was diagnosed with Williams Syndrome when he was four weeks old.
"He had his heart surgery when he was a baby," Self told "20/20." "Last year they put two stents in and, during the process, he had a stroke. So I had a nine-year-old that had a stroke. We had to re-teach him to speak, to walk, to use his hands."
Now 11, Alex rides a bike, plays drums and piano, and attends a regular school.
Learn more about Alex, Kelley Martin and Williams Syndrome on "20/20" tomorrow at 10 p.m. ET.