On June 26, 2007, Wendy Chung, director of clinical genetics at Columbia University, drove to the New York City borough of Queens with a delicate request for the Croatian matriarchs of a star-crossed family. She asked the two sisters, one 82 and the other 89, if they would donate some of their skin cells for an ambitious, highly uncertain experiment that, if it succeeded, promised a double payoff. One, it might accelerate the search for treatments for the incurable disease that ran in their family. Two, it might establish a valuable new use for stem cells: unspecialized cells able to give rise to many different kinds of cells in the body. “We had a very nice lunch and literally went back to the house and took the biopsies,” Chung remembers. As they sat around the dining-room table, the elderly sisters were “very happy sticking out their arms,” recalls the daughter of the 82-year-old woman. The younger sister told Chung: “I get it. Go right ahead.”

The sisters suffered from amyotrophic lateral sclerosis (ALS), a degenerative and slowly paralyzing nerve disorder that is also known as Lou Gehrig’s disease, after the Yankee slugger who was told he had it in 1939 and died two years later. The 89-year-old showed few signs of the disease, whereas her 82-year-old sister had trouble walking and swallowing.