Video report by ITV News Science Editor Tom Clarke
"I’m always cutting myself, burning myself, falling over, hurting myself."
For years Jo Cameron believed she was just "clumsy" and "had no idea that there was anything unusual" about how little pain she felt.
Throughout the 71-year-old's life she often did not notice cuts or burns until she could smell burning flesh, but when she did injure herself, she tended to heal very quickly.
Yet it was only at the age of 66 when Ms Cameron - who lives near Loch Ness in Scotland - had surgery on her hand and reported no pain afterwards, that she was diagnosed with pain insensitivity by her anaesthetist, Dr Devjit Srivastava.
Dr Srivastava - who also specialises in pain medicine - referred Ms Cameron to pain geneticists at UCL and the University of Oxford.
Watch how ITV News Science editor Tom Clarke and producer Sophie Alexander did in a pain tolerance test.
Scientists conducted genetic analysis and found that Ms Cameron has a mutation in a previously-unidentified gene.
Researchers found that she has a "micro-deletion", or a tiny bit missing, in a pseudogene - a segment of DNA which is related to a gene but does not have the full functionality of a regular one.
Scientists dubbed this FAAH-OUT, and also found Ms Cameron had a mutation in the neighbouring gene that controls the FAAH enzyme.
The FAAH gene is well-known to pain researchers, as it is involved in endocannabinoid signalling which is central to pain sensation, mood and memory, meaning that Ms Cameron also experiences very little anxiety or fear and may have enhanced wound healing.
She was given the lowest score on a common anxiety scale, and told researchers she never panics, even in dangerous situations such as a recent traffic incident.
The pensioner also reported memory lapses throughout life such as forgetting words or keys, which has previously been associated with enhanced endocannabinoid signalling.
She said: "I had no idea until a few years ago that there was anything that unusual about how little pain I feel - I just thought it was normal.
"Learning about it now fascinates me as much as it does anyone else.
"I would be elated if any research into my own genetics could help other people who are suffering."
Scientists have found mice that do not have the FAAH gene have reduced pain sensation, accelerated wound healing, enhanced fear-extinction memory and reduced anxiety.
Dr James Cox of UCL Medicine, one of the lead authors of the paper, said: "We found this woman has a particular genotype that reduces activity of a gene already considered to be a possible target for pain and anxiety treatments.
"Now that we are uncovering how this newly-identified gene works, we hope to make further progress on new treatment targets.
"We hope that with time, our findings might contribute to clinical research for post-operative pain and anxiety, and potentially chronic pain, PTSD and wound healing, perhaps involving gene therapy techniques."
The researchers say it is possible there are more people with the same mutation and urged anyone who does not experience pain to come forward.
The study is published in the British Journal of Anaesthesia.