The Blockers got rid of all their furniture with sharp corners. They lay down the softest carpet they could find. They didn’t let Ashlyn roller-skate. They didn’t let her ride a bicycle. They wrapped her arms in layers of gauze to keep her from rubbing them raw. They used a baby monitor in her bedroom to listen for grinding teeth. When they still couldn’t sleep, they brought her into their bed, and Tara held her hands over Ashlyn’s, cupping them so she wouldn’t chew on her skin or rub her eyes during the night.

When Ashlyn was 5, the Blockers decided the only way they were ever going to find another person in the world like her was to send up a flare. They contacted their local newspaper, The Blackshear Times, which ran an article about Ashlyn in October 2004. The Associated Press picked it up, and Tara remembers Ashlyn’s picture next to George Bush’s and John Kerry’s on the MSN home page. Ashlyn’s grandmother in Virginia saw it while she was at work and called Tara in Georgia. “Do you know Ashlyn’s on the Web?” she asked. “ ‘The Girl Who Feels No Pain!’ Turn on your computer!” By that time, of course, the Blockers knew. “Good Morning America” had already called.

The Blockers were flown to New York City and appeared on “G.M.A.” — and on the “Today Show” and “Inside Edition.” They told and retold the stories about Ashlyn’s injuring herself. When they flew back to Jacksonville, people recognized them in the airport. They were interviewed by a French news crew and by the BBC. A Japanese film crew brought bamboo chopsticks as a gift. They were called by Oprah but never made it on. They said yes to Geraldo Rivera and no to Maury Povich. Ashlyn was in the Jan. 24, 2005, issue of People, the famous one with Brad Pitt and Jennifer Aniston on the cover, under the giant yellow headline “Brad & Jen: Why They Split.”

All the media attention finally put the family in touch with scientists who could help them understand her condition. Dr. Roland Staud, a professor of medicine and rheumatologist at the University of Florida, heard about Ashlyn and invited the Blockers to Gainesville, where for 15 years he has been conducting research into chronic pain. The implications of her condition were profound. She was an anomaly of nature. Over the next few years, Staud tested Ashlyn’s genetic material and eventually found two mutations in her SCN9A gene. That same gene, mutated in a different way, led to severe pain and chronic pain syndromes. If he could understand how the mutation worked in Ashlyn, Staud theorized, he might be able to turn it off in people with chronic pain.

The connection between the gene and pain insensitivity was discovered in 2006 by a geneticist in Cambridge, England, named Geoffrey Woods. “I used to work in Yorkshire, where lots of Pakistanis had emigrated” and where there were a number of marriages between first and second cousins, Woods told me when we spoke this fall. “I’d see an awful lot of children with genetic diseases.” An obstetrician who had come to England for training persuaded Woods to do some research in Pakistan. On one of his trips, he was asked to see a boy in Lahore who, they said, didn’t feel pain. “I agreed to see him and went out,” Woods said. The boy’s mother and father greeted him but told him the boy had died.

“For his birthday, he’d wanted to do something for his friends — he’d wanted to jump off the first-floor roof of his house,” Woods told me. “And he did. And he got up and said he was fine and died a day later because of hemorrhage. I realized that pain had a different meaning than I had thought. He didn’t have pain behavior to restrain him. When I came back to the U.K., I found three more families with kids in the same condition — with multiple injuries, biting lip, biting tongue, biting hands, fractures, scars. And in several cases, parents almost had their children removed because of suspected child abuse.”

Woods and his colleagues began their search for the genes that caused this disorder, eventually zeroing in on SCN9A. Pain-sensing nerves along the body’s surface normally fire more frequently when we touch something hot or sharp, sending electrical signals to the brain, causing us to react. These electrical signals are generated by molecular channels produced by the SCN9A gene, says Stephen G. Waxman, a professor of neurology at Yale University School of Medicine. Ashlyn’s mutation prevents the gene from making the channel, and the electrical impulses are never produced.