Scientists have identified a genetic defect that prevents some people from feeling any physical pain, while leaving them perfectly normal otherwise. Sound like a blessing? It's not.

In Thursday's issue of the journal Nature, scientists who found the gene describe six related children who have never felt pain in their lives because of the very rare disorder. The children come from three families with roots in northern Pakistan.

Their experience illustrates that pain is an important warning of injury, disease or danger that signals people to save themselves from further injury. Life without that signal, the report shows, is dangerous.

Because the children felt no pain from biting themselves, for example, all six had injuries to their lips, some requiring later plastic surgery. Two had lost one-third of their tongues.

Most had suffered fractures or bone infections that were diagnosed only later on because of limping or lack of using a limb.

Some also had been scalded by boiling liquids or steam, or burned from sitting on radiators, said C. Geoffrey Woods, a geneticist at the Cambridge Institute for Medical Research in England. He and colleagues wrote the Nature report.

Woods had been asked to see another patient, a boy who took advantage of the condition by performing street theater, piercing his arms with knives and walking on burning coals. But the boy died before Woods saw him, after jumping off the roof of a house on his 14th birthday.

Detailed examinations of the six children showed that their nervous systems appeared otherwise normal. They could perceive touch, warm and cold, tickle and pressure, for example.

DNA from the children and their parents was used to track down the genetic defect, which sabotages the ability of a protein to perform a key job in pain signaling.

It was not clear whether the children still live in Pakistan.

Medical journals have recorded only a handful of people with a lifelong inability to feel pain. The first report was apparently in 1932, about a patient who made a living as a human pincushion act. A crucifixion had to be canceled after a spike was driven through one hand, because a woman in the audience fainted.

It's not clear whether any of the previously reported cases were caused by the newly identified genetic defect, Woods said. Nor is it clear how many people have this defect, although it's probably very rare, he added.

Still, knowledge about the defect and its impact might help scientists develop better painkillers, he and colleagues suggested.