Sam Berns's life was improbable. He was born with progeria, a disease of rapid premature aging that only about 250 children worldwide are known to have.

Even more improbable: Both his parents were pediatricians, well-placed in the medical mecca of Boston and hell-bent on finding answers to their son's condition.

"The key word here is 'improbability,'" says John Seng, a member of the Progeria Research Foundation's board. "[Perhaps] one out of four million children are born with this disease, but he was spot on, born to Leslie Gordon and Scott Berns."

Sam died last Friday at the age of 17—an unusually long life considering that most progeria patients die at an average age of 13. Before he died, he built entire