People with Williams Syndrome treat strangers as their new best friends. Now the condition is revealing clues to our evolutionary past – and what makes us human.

A rare genetic disorder, Williams Syndrome, affects around 1 in 7,500 to 10,000 people worldwide. It is caused by the deletion of a small segment of chromosome 7, which contains 25–27 genes.

An estimated 20,000 to 30,000 people in the United States have Williams syndrome, which is diagnosed with genetic testing. Learn more about the center on Penn Medicine's website.