Dr. Srivastava referred her to University College London’s Molecular Nociception Group, a team focused on genetic approaches to understanding the biology of pain and touch. They had some clues for her. In recent decades, scientists have identified dozens of other people who process pain in unusual ways. But when Dr. James Cox, a senior lecturer with that group and another author of the new paper, inspected her genetic profile, it did not resemble that of others known to live without pain.

Eventually he found what he was looking for on a gene the scientists call FAAH-OUT. All of us have this gene. But in Ms. Cameron’s, “the patient has a deletion that removes the front of the gene,” he said. Additional blood work confirmed this hypothesis, he said.

Ms. Cameron said she had been shocked by the interest in her case. Until her conversation with Dr. Srivastava, pain was not something she thought about. Perhaps it helped that even though she burned and cut herself quite often, her injuries rarely left scars — something else that scientists believe is connected to the mutation.

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A number of articles have been written about parents of children with similar conditions. Many live in fear that without pain, their children won’t learn how to avoid hurting themselves. Her parents never made it an issue, she said. She suspects this may be because she inherited the mutation from her father.

“I can’t remember him needing any painkillers,” she said. “I think that’s why I didn’t find it odd.”

Unfortunately, because he died before the discovery, it will remain unknown whether he carried the mutation. Her mother does not share it. Neither does her daughter. Her son “has the same microdeletion in FAAH-OUT, but does not have the other mutation that confers reduced FAAH function,” Dr. Cox said.

In other words, her son shares some, but not all, of her pain insensitivity.

Scientists are also intrigued by Ms. Cameron’s extraordinarily low anxiety level. On an anxiety disorder questionnaire, she scored zero out of 21. She cannot recall ever having felt depressed or scared.