Jo Cameron has never felt pain. Not after wrist surgery, not when she had her hip replaced – not even giving birth to her children. The 71-year-old Scottish woman also experiences very little anxiety or fear, and her body appears to heal quickly.

New research is shedding light on the genetic reasons why that is. Scientists say it's caused by a mutation in a previously unidentified gene. Like a lot of medical discoveries, this came to light by chance, an alert doctor and a very unusual patient who refused drugs after surgery, reports CBS News' Elizabeth Palmer.

"I felt things. I felt my body stretching, I felt peculiar feelings, but nothing to make me – no pain," she said.

Researchers at London's University College found a bit missing from one of her genes that affected Jo's body chemistry, so she simply doesn't feel what the rest of us call pain.

Sitting beside her husband in a doctor's office, the same hot chilis she's happily chewing make her husband wince. A pain-free life may sound great but it does have a downside. Jo often doesn't realize when she's hurt herself.

"I'm ironing and quite often and I'm sort of ironing away and suddenly find I've ironed my arm – and it's only when I see afterwards a sort of mark down there that I see that I've ironed my arm," Cameron said. But for doctors, this is an exciting discovery.

"There's a vast problem of around about six or seven percent of the population have ongoing excruciating pain so we really do need some new therapies," said University College London professor John Wood.

Millions of patients in both chronic and acute pain have to rely at the moment on addictive drugs.

"We hope that we'll be able to help people in the future by harnessing the knowledge that we gain from the mutation in Jo, and trying to mimic it either through gene therapy or potentially in a pharmacological way," Wood said.

While this is an intriguing discovery we're probably years and many millions of dollars away from it translating into treatment. But it's certainly a ray of light for people plagued with pain.